ACCEPTANCE: AN HISTORICAL AND CONCEPTUAL REVIEW
Transcription
ACCEPTANCE: AN HISTORICAL AND CONCEPTUAL REVIEW
IMAGINATION, COGNITION AND PERSONALITY, Vol. 30(1) 5-56, 2010-2011 ACCEPTANCE: AN HISTORICAL AND CONCEPTUAL REVIEW JOHN C. WILLIAMS VA Healthcare System, Long Beach STEVEN JAY LYNN State University of New York at Binghamton ABSTRACT Recognition of the value of acceptance of the self, others, and the flux of human experience, has philosophical and religious roots that date back thousands of years. The past two decades have witnessed a swell of interest in acceptance, as evidenced by an increase in acceptance-based therapeutic interventions, and a growing appreciation of the paradoxical nature of acceptance and personal change and the role of experiential avoidance in psychopathology. In this article we review historical and contemporary descriptions and definitions of acceptance, measures of acceptance, the relation between acceptance and change, and the role of acceptance in psychopathology and psychotherapy. Our central objective is to delineate a rich conceptual scheme that encompasses the diverse ways in which acceptance has been explicated in classical and contemporary writings, and to highlight the need for further validation of this useful and popular construct. The notion that acceptance—of oneself, other people, circumstances, and the world at large—can be a force for personal change has deep roots in Eastern and Western culture. The benefits of acceptance are described in religious texts (e.g., Buddhist Sutras, Bhagavad Gita, New Testament, Tao Te Ching, Yoga 5 Ó 2010, Baywood Publishing Co., Inc. doi: 10.2190/IC.30.1.c http://baywood.com 6 / WILLIAMS AND LYNN Aphorisms), philosophical tracts (e.g., Aurelius, Epictetus, Keirkegaard, Krishnamurti, Lao Tzu, Watts), and literary works (e.g., Austen, Nabokov, Pirsig, Shakespeare, Steinbeck, Tolstoy) across diverse eras and cultures. In the psychological literature, acceptance has intrigued scholars for the better part of a century. Although a diverse group of theorists have contributed to understanding the salutary effects of acceptance (e.g., Ellis, Freud, Horney, James, Skinner), typically humanistic and existential theorists, particularly Carl Rogers, are credited with elaborating acceptance as a mechanism of selfactualization and therapeutic change. More specifically, early quasi-experimental work (e.g., Hall, 1918; Young, 1924), theory development (Rogers, 1944b; Wilson, 1942), and measurement (e.g., Berger, 1952; Fey, 1954; Phillips, 1951; Sheerer, 1949; Stock, 1949) led to the validation of two specific constructs: self-acceptance and acceptance of others, which centered on developing an awareness of both the positive and negative aspects of the self and others while maintaining an attitude of positive regard. Whereas these two constructs have persisted in the literature, over the past two decades a new wave of interest in acceptance has emerged, most notably in what has been described as the “third wave” of behavioral and cognitive behavioral approaches and selfregulation techniques (e.g., Hayes, 2004b; Hayes, Jacobson, Follette, & Dougher, 1994). Recent empirical research generally has focused on the efficacy of acceptance-based psychotherapeutic treatments. Less attention has been paid to the validity of the construct itself, even as contemporary theorists appear to have broadened the scope of the construct to embrace more classical notions of acceptance and mindfulness, another construct with deep roots in philosophy and religion. During the initial resurgence of interest in acceptance, Wulfert (1994) observed that there was no universal definition of acceptance. A variety of definitions can add to the richness of meaning and nuance of acceptance, but if a construct becomes overbroad, multiply defined, with overlapping components, it can lead to poor specificity—that is, it can come to mean everything and nothing. Although a number of researchers have attempted to define, operationalize, and measure acceptance, there has been no reasonably comprehensive and systematic framework for understanding the broader, perhaps multifaceted, construct of acceptance that is presented in the extant literature. Our purpose is to review research and theory pertaining to the construct of acceptance in order to provide, if not an empirically-based organizational framework—as such an effort would be premature—at least a digest of issues relevant to acceptance construct validity (as even this has not yet been attempted), and to suggest directions for further research. We will proceed by first addressing definitional issues, the variable usage of the term acceptance in psychology, and basic denotations. We then turn to the historical aspects of acceptance, its validation in the 20th century, and finally to its current status, before we conclude with recommendations for future research. ACCEPTANCE: AN HISTORICAL AND CONCEPTUAL REVIEW / 7 DEFINING ACCEPTANCE The term acceptance has a number of definitions. The etymological root of accept is the Latin acceptare, the Old French accepter, and finally the Middle English accept used by Chaucer and Wyclif in the 14th century (Onions, 1966). To accept is “to receive willingly or with approval,” to take toward (i.e., ac + capere) rather than cast away (p. 7). Four modern definitions (Brown, 1993; Merriam-Webster, 1993; Weiner & Simpson, 1991) bear directly on the present discussion: 1. taking or receiving something, as a pleasure, a satisfaction of a claim, or a duty; 2. favorable reception, regard, or approval; 3. assenting to or believing; and 4. acceptableness. These four definitions are found in a number of branches of psychology. For example, one branch of social psychology deals with individuals’ acceptance of group norms in the form of conformity, compliance, identification, and internalization (e.g., Brown, 1936; Cialdini & Goldstein; 2004; Hollander, 1960; Kelman, 1958; Menzel, 1957; Sherif, 1936). In another branch, social acceptance refers to the effects of being or not being accepted by others, such as parental acceptance of children (e.g., Burchinal et al., 1957), peers’ acceptance of adolescents (e.g., Kuhlen & Lee, 1943), or society’s acceptance of the disabled (e.g., Ladieu et al., 1948), or mentally ill (e.g., Roman & Floyd, 1981). In clinical psychological science, the treatment compliance literature employs the term acceptance to describe the extent to which a mental health patient is willing to comply with medical, psychiatric, or psychological interventions (e.g., Baile & Engel, 1978; Demyttenaere, 1997; Hunter, 1942; Imber et al., 1956; Scheel et al., 2004). Other uses of the term vary broadly, from specific disciplines, such as design acceptance (e.g., Madni, 1988), job acceptance (Marozas & May, 1980), and technology acceptance (e.g., Colvin & Goh, 2005), to broader scientific issues relevant to all disciplines such as the “acceptance” of theories (e.g., Chow, 1992), models (e.g., Lynn & Fite, 1998), techniques (e.g., Hudson et al., 1998), and measures (e.g., Dahlstrom, 1992). Whereas all of these forms of acceptance conform in one way or another to the definitions given above, they may be distinct research areas or broad principles with little or no bearing on the type of acceptance under consideration here. As such, they may be considered beyond the boundaries of the construct discussed in this review. Experiential Acceptance A title/keyword search of “acceptance” in PsychINFO returns over 28,000 citations, a substantial proportion of which are not relevant to the present discussion. This may stem from the fact that the form of acceptance under consideration 8 / WILLIAMS AND LYNN lacks a modifying adjective (e.g., self-acceptance, social acceptance, technology acceptance) to distinguish it from other more general uses. For the purposes of this discussion, we prefer the term experiential acceptance, recently used by BlockLerner and others (Block-Lerner, Salters-Pedneault, & Tull, 2005; Cardaciotto, 2005; Roemer & Orsillo, 2007). In addition to distinguishing it from other forms of acceptance, this term also captures an essential aspect of the construct that is not necessarily shared by other forms of acceptance; namely, that the primary object of acceptance is experience itself (rather than any particular stimulus). This adjective is also used in the term experiential avoidance (Chapman, Gratz, & Brown, 2006; Hayes, Strosahl, Wilson, Bisset, Pistorello, Toarmino, et al., 2004a; Hayes, Wilson, Gifford, Follette, & Strosahl, 1996; Tull & Roemer, 2003), which is a key component of contemporary theoretical and empirical contributions to the construct of acceptance. At the outset, it bears emphasis that acceptance of a stimulus is not the same as condoning it or deeming it in any way acceptable: to experientially accept a stimulus means to acknowledge that a stimulus is present, rather than apply any evaluative designation. ANCIENT RELIGIOUS AND PHILOSOPHICAL PRECURSORS A variety of ancient philosophical and religious sources consider acceptance to be integral to personal and social development. Spanning millennia as well as continents, they also emphasize different aspects of acceptance, or define it in different ways. A brief discussion of these aspects of acceptance may help to contextualize the current conceptualizations, as these basic principles appear with some regularity in modern and contemporary treatments of psychological acceptance. The main concepts that comprise acceptance as a philosophical and religious principle can be described in terms of nonattachment, nonavoidance, nonjudgment, tolerance, and willingness. Nonattachment Twenty-five hundred years ago, the Buddha attributed human suffering to the tendency to cling to thoughts, people, sensory objects, and habitual ways of acting and feeling in the world. The Buddha’s observations echoed earlier Hindu, Vedic, and Yoga philosophies, which enjoined practitioners to withdraw the mind from evanescent sense objects in order to refocus it on the one true object, the divine. Often embodied in formal meditation practices, nonattachment was taught as a path to mental discipline, internal quiescence, and ultimately to enlightenment. In principle, because all possessions and people are created and destroyed, are born and die, any attempt to hold onto things or people is pointless and leads inevitably to suffering. To practice nonattachment is to accept that the objects of experience wax and wane, and that to allow them to come and go ACCEPTANCE: AN HISTORICAL AND CONCEPTUAL REVIEW / 9 naturally is preferable to any attempt to control or retain them. In Taoist thought, the sage accepts the world, and the ebb and flow of things, without holding on. Interestingly, Seng-Tsan, The Third Zen Patriarchs observed that this includes everything, and that “even to be attached to the idea of enlightenment is to go astray” (Kornfield, 1993, p. 149). Nonavoidance Like nonattachment, nonavoidance is a valued activity in Eastern and Western contemplative traditions. Marcus Aurelius (trans. 1965) wrote that passing one’s days in pursuit or avoidance leads to a disturbed mind and an unhappy existence. Nonavoidance and nonattachment can be seen as complementary, depending on whether or not one is fleeing toward or from a given stimulus. In Eastern classical literature, in fact, attachment tends to be the central construct, and avoidance is regarded as a particular form of attachment. An avoidance of insects, for example, could reflect an attachment to a real or imagined insect-free environment. Like nonattachment, nonavoidance can be defined as refraining from a pointless and maladaptive behavior, running away when no physical threat is present. This, combined with the maladaptive “running toward” of attachment, results in a definition of acceptance as the capacity to remain available to present experience, without attempting to terminate the painful or prolong the pleasant. Though both nonattachment and nonavoidance may require effort, both can be defined therefore as a nondoing. As Lao Tzu put it, “The Master does his job and then stops” (trans. 1988, p. 30). Nonjudgment Nonjudgment is a theme in both the Eastern and Western canon. Matthew (7:1) wrote “judge not that ye may not be judged,” Hamlet described the kingdom of Denmark as a prison, reasoning “nothing is either good or bad, but thinking makes it so” (William Shakespeare, 1989, p. 250), and Lao Tzu succinctly captured the spirit of nonjudgment when he observed that the “mark of a moderate man is freedom from his own ideas” (trans. 1988, p.59). Nonjudgment is central to modern conceptualizations of acceptance: it is a conscious abstention from the categorization of experience as good or bad, or right or wrong. Aurelius advised to refrain from internally embellishing our sense impressions with internal commentary. Nonjudgment involves describing stimuli rather than adding evaluations of them. Nonjudgment is a central component of mindfulness meditation, and can be found in the Zen concept of fushizen-fushiaku, literally “not thinking good, not thinking bad,” which represents a transcendence of distinguishing phenomena as good and bad (Fischer-Schreiber, Ehrhard & Diener, 1991, p. 74). As Seng-Tsan, the Third Zen Patriarch observed, “the burdensome practice of judging brings annoyance and weariness” (Kornfield, 1993, p. 150). 10 / WILLIAMS AND LYNN Tolerance Acceptance requires that a person tolerate experiences as they are given; otherwise one simply pursues pleasure, flees pain, and becomes more caught up in judging experiences than in having them. The Stoics (e.g., Marcus Aurelius, trans. 1965; Epictetus, trans. 1950; Seneca, trans. 1920) valued the ability to tolerate or willingly withstand experiences because it increases self-control, detachment from emotion, and indifference to pleasure and pain. Epictetus suggested selecting the worst seat at a social gathering, such as one without shade, in order to develop an indifference to the sun and heat. Similarly, an avoidance of snakes might diminish if one were able to tolerate progressive contact, similar to modern behavioral exposure methods. Because acceptance involves making contact with reality just as it is in the moment, it is necessary, lest one lapse into avoidance, to be able to remain present and aware even when the stimuli available are less than desirable Accordingly, tolerance can be considered an ability to remain present and experience whatever is occurring in the moment. Note, however, that this ability is not equivalent to resignation or helplessness in the face of the aversive. It is a choice, which does not preclude concurrent efforts to change what is occurring. Tolerance can be built up or acquired through willing exposure to a wide variety of experiences, or to specific troublesome stimuli. In this sense, tolerance is something that can be practiced as well as acquired. Willingness If one wishes to escape from one experience or lose oneself in another, this is often possible. Acceptance, therefore, is a choice. Epictetus (1950) wrote that when one is invited to entertainment, one should take what one finds. That is, one should choose to participate in a event, even if it is not exactly to one’s taste. For the Stoics, in fact, exercise of the will was paramount. Acceptance involves a free choice. That said, willingness may well involve surrender or compliance, so long as it is not coerced. Marcus Aurelius (1965) wrote, for example, that our freedom is never compromised when we follow the direction of someone who puts us right. The benefits that can accrue from allowing another person to guide one’s behavior are integral to a host of spiritual traditions. In Eastern meditative practices, for example, one accepts the instructions of a master and agrees neither to add nor subtract from his or her instructions. Similarly, Blaise Pascal (trans. 1966) accepts the counsel of his spiritual director because he considers the directives to be essential to his spiritual development. Whether directed by another, or simply determined by what is present, acceptance includes the willingness to have an experience. Limitations It is difficult to say which of these ancient concepts should be considered central components of contemporary acceptance and which may be better accounted for ACCEPTANCE: AN HISTORICAL AND CONCEPTUAL REVIEW / 11 by other constructs or are separate constructs in their own right. Additionally, ancient acceptance includes elements that may be considered more radical, paradoxical, and profound than contemporary psychological science has conceptualized. For example, Zen philosophy describes the world as perfect as it is, without need of change, and practitioners may expect to have this realization as they progress. Moreover, continuous, unbroken states of acceptance are described in the classical literature of the East and are associated with states of enlightenment. Modern psychological literature, in contrast, usually describes the effects of acceptance in terms of behavioral adaptivity, self-actualization, or well-being. In the classical Western literature, acceptance can be seen in the extreme nonattachment of religious celibacy and the renunciation of possessions, and most profoundly in the lives of saints and martyrs who have accepted, even welcomed, gruesome experiences, such as torture and violent death. The modern psychological literature has not dealt with such extreme forms of acceptance, although there may be some overlap in the form of radical acceptance (e.g., Brach, 2003; Linehan, 1994), which is sometimes used to describe a Zen-like state of acceptance, usually periodic, consisting of a thorough willingness to experience whatever occurs in the moment. Ancient forms of acceptance also include elements of paradox (e.g., the Taoist notion that the greatest form of help is to give up helping, and that as the sage bends he is straightened) which may or may not be compatible with contemporary conceptualizations of acceptance. Pantanjali, the 2nd century author of the Yoga Sutras, the original manual of yoga, wrote that “yoga is the control of thought waves in the mind” (Prabhavananda & Isherwood, 1981, p. 15), and that one goal of yoga practice over an extended period of time is the cessation of thought altogether. At first glance, these statements might seem at odds with modern principles of acceptance, given that thought control is sometimes maladaptive (e.g., thought suppression and rebound effects; Wegner, Schneider, Carter, & White, 1987), and thoughts are generally considered to be mental events to be accepted rather than eliminated. In the case of yoga philosophy, however, thoughts are controlled by allowing them to come and go without absorption: they are released the moment they arise, usually by redirecting the attention to a predetermined object, such as the breath. In fact, the ability to accept and experience thought content without reservation may be considered a pre-requisite for this practice. These points may be as yet more esoteric than discussion in terms of the empirical findings may allow. Nevertheless, we are left with a rather interesting compound paradox: that we are to accept internal events in order to be rid of them, and we control them by letting go. In conclusion, acceptance to the ancients was a notion integrated into the fabric of religion, philosophy, folk tradition, and daily life. Although the benefits of acceptance were empirical, in the sense that they were wrought from collective experience, they were not, of course, subjected to a modern scientific method. Moreover, coming from diverse cultural and linguistic traditions, the various 12 / WILLIAMS AND LYNN historical contributions are difficult to assemble into a single ancient construct. That said, researchers and theorists in psychology have defined and operationalized acceptance in part by drawing on these ancient conceptualizations. Therefore, they are useful to examine as we seek to describe acceptance as it is conceptualized today. ACCEPTANCE IN THE 20TH CENTURY Turning now to a brief history of acceptance in 20th century psychology, we leave a gap of nearly 2,000 years. One reason is that acceptance theorists tend to cite sources from the classical rather than medieval or modern philosophy. Additionally, a review of acceptance across all of Eastern and Western philosophy is beyond the scope of this article. To our knowledge, such a review has not been attempted, even though a number of authors do discuss aspects of the philosophical history of acceptance in their treatments of the construct (in particular, see Dryden & Still, 2006; Ellis, 2000). In a similar vein, acceptance can be found across a spectrum of psychological theories. Moreover, psychological treatments almost always rely on the willingness of the patient to participate in the therapy, and, perhaps to a lesser extent, on the patient’s awareness and acknowledgment of the problem under treatment. Our goal, therefore, is not to catalog the construct of acceptance in every corner of psychology. Rather, we trace the development of the construct in the psychological literature, noting in particular some of the conceptualizations that have taken hold over the 20th century, with special attention to the discipline of clinical psychology and experiential acceptance. 1910s Although acceptance was not his focus, Freud (1910/1965) could have been writing about nonattachment when he wrote that “every single hysteric and neurotic . . . not only do they remember painful experiences of the remote past, but they still cling to them emotionally; they cannot get free of the past and for its sake they neglect what is real and immediate” (p. 17). Freud (e.g., 1913/1957a, 1914/1957b) also contributed to the notion that acceptance of others was related to self-acceptance, and that avoidance can be maladaptive. In a similar vein, Hall (1918) indicated that nonavoidance of aversive stimuli had potential benefits; for example, confronting rather than avoiding the stimuli of death during wartime aided a soldier or citizen in accepting the possibility of his or her own death. As a result, he or she became “very familiar with the thought that he may be the next victim and so accepts the fact with growing equanimity” (p. 373). He further suggested that acceptance of death lifted the spirits and improved performance in life-threatening situations. Early in the century, then, there was an indication that acceptance in these forms (nonattachment and ACCEPTANCE: AN HISTORICAL AND CONCEPTUAL REVIEW / 13 nonavoidance) was potentially beneficial and that the opposite could lead to neurotic symptoms and distress. 1920s and 1930s In the 1920s and 1930s, the term acceptance sometimes was used to describe a way of behaving or relating to stimuli that emphasized openness toward reality rather than defensiveness, negation, or denial (Ferenczi, 1926; Penrose, 1927). Whereas a lack of acceptance was associated with intrapsychic conflict and pathology, acceptance of oneself and one’s situation contributed to positive outcomes in mental health, such as adjustment after a divorce (Waller, 1930), treatment for alcoholism (Grant, 1929), or personality disturbance (Tidd, 1937). As such, self-acceptance was discussed as a therapeutic goal in the context of psychodynamic psychotherapy (e.g., Rank, 1945; Taft, 1933). Even in these early years, some noted the potential difficulties associated with assessing acceptance in individuals. Peck (1929), for example, raised the concern that a patient could appear more defensive while actually growing in acceptance, which can be contrasted with later investigations of the role of social desirability in the measurement of acceptance (Crowne & Stephens, 1961); in particular, that high selfreported self-acceptance in fact may reflect defensiveness or lack of insight (Zuckerman & Monashkin, 1957). Early acceptance theorists also began to posit a positive correlation between self-acceptance and acceptance of others (e.g., Adler, 1926; Fromm, 1939; Horney, 1937). 1940s In the 1940s, acceptance figured in the study and treatment of military personnel during and after World War II. Wilson (1942), for example, wrote that admitting and accepting the experience of fear associated with air raids was a protective factor against stress disorders among civilian populations. Rogers (1944a) and his colleagues (Rogers & Wallen, 1946) noted a host of adjustment problems faced by returning soldiers, including hostility, vocational uncertainty, marital and family problems, and disabilities due to injuries. Among the major treatment recommendations was to facilitate the patient’s acceptance of the daunting feelings engendered by the war and also by the transition back to civilian life. Beyond military applications, Rogers (1940, 1943, 1944b, 1947) and others (e.g., Snyder, 1947) began to place the development of self-acceptance in a position of primary importance in the therapeutic process. Rogers wrote that a client should “admit his real self with its childish patterns, its aggressive feelings, and its ambivalences, as well as its mature impulses, and rationalized exterior” (Rogers, 1940, p. 162). For Rogers, self-acceptance was “the foundation of insight” (Rogers, 1940, p. 163). Moreover, the “self” in self-acceptance included the acknowledgment and experiencing of the entirety of internal experience, not simply an esteemed self-concept. Beyond the self, acceptance extended to external 14 / WILLIAMS AND LYNN stimuli, such as other people (i.e., acceptance of others), which he described as a subjective process not dependent on the pleasantness or unpleasantness of the environment, but rather on one’s attitude toward it. Like others before him, Rogers also hypothesized that acceptance of self and of others should be correlated positively; that is, a person with high self-acceptance should be more likely to be accepting of others (Rogers, 1951). Finally, Rogers theorized that the development of self-acceptance and acceptance of others leads to a more realistic, and perhaps paradoxically more positive, view of the self and others. That is, although the term self-acceptance is sometimes used synonymously with self-esteem or positive self-regard, Rogers emphasized frank knowledgment of the self as it is. 1950s In the 1950s, the self-acceptance and acceptance of others constructs were subject to further theory development, empirical investigation, and scale development. A host of theorists were cited during this period, including Adler, Ellis, Horney, Fromm, Perls, Rogers, and Sullivan (e.g., Berger, 1952; Fey, 1954; see also Dryden & Still, 2006). Several lines of research were initiated, driven by hypotheses about: a) positive correlations between self-acceptance, acceptance of others, and acceptance by others; b) negative correlations between self-acceptance and psychopathology; and c) the relation between acceptance and other constructs. These investigations used a variety of self-report and informant questionnaires and checklists, often developed for the purpose of testing specific hypotheses. Several of these scales became standard measures of self-acceptance and acceptance of others, such as the scales constructed by Berger (1952), Fey (1954), and Phillips (1951). The findings from empirical investigations supported predictions about acceptance, with a few notable exceptions. First, self-acceptance and acceptance of others were found to be positively correlated (e.g., Fey, 1954; Kennedy, 1958; Omwake, 1954; Sheerer, 1949; Trent, 1957; Williams, 1962), with correlations in the range of .30–.60 across most studies. In contrast, however, acceptance by others (that is, ratings of a participant by others, as opposed to ratings of perceived acceptance by the participant) was not found to be correlated with either self-acceptance or acceptance of others (Omwake, 1954; Williams, 1962). Second, group comparisons found high self-accepters to be significantly lower on measures of psychopathology (Berger, 1955; Bills, 1953; Zuckerman & Monashkin, 1957; Zuckerman & Oltean, 1959). Third, a number expected associations with other constructs emerged. For example, self-acceptance was determined to be associated with childhood adjustment (Taylor & Combs, 1952), marital happiness (Eastman, 1958), and frustration tolerance (Doleys & Kregarman, 1959). Some unexpected associations were found, such as a finding that self-accepting underachievers grossly overestimated their grades (Mitchell, ACCEPTANCE: AN HISTORICAL AND CONCEPTUAL REVIEW / 15 1959); and some expected associations were not found, such as therapists higher in self-acceptance and acceptance of others were not rated as better therapists by supervisors (Streitfeld, 1959). 1960s In the 1960s, investigators continued to examine the relationships between self-acceptance, acceptance of others, psychopathology, and other constructs. Empirical investigations continued to find that self-acceptance and acceptance of others were correlated, and that neither was correlated with acceptance by others (Rubin, 1967; Suinn, 1961; Suinn & Hill, 1964; Williams, 1962). Some of these studies broadened the validity of this relationship beyond self-report and laboratory studies to experimental interactions with specific groups, such as the mentally ill (Holzberg, Gewirtz, & Ebner, 1964), to specific others, such as a child’s parents (Medinnus & Curtis, 1963), and to naturalistic studies on college campuses (Graham & Barr, 1967). A number of predicted associations with additional constructs also were examined. Several researchers found that acceptance and anxiety were negatively related (Ohnmacht & Muro, 1967; Pilisuk, 1963). Interestingly, Suinn and Hill (1964) also found that that anxiety disrupted the relationship between self-acceptance and acceptance of others: increased anxiety was associated with greater decreases in self-acceptance than in acceptance of others. Berger (1961, 1963) found that willingness to accept limitations was associated with college achievement, but the relationship seemed to hold for liberal arts students but not engineering students. Other investigations failed to find some expected relationships, and in the process the nomological network (Cronbach & Meehl, 1955) of acceptance became more specific. Among these relationships, self-acceptance: a) did not predict performance under stress (Goldfarb, 1961); b) was not affected by experimentally induced success and failure experiences (Solway & Fehr, 1969); and c) was not related to hypnotizibility (Vingoe, 1967). Also during this period, a number of investigators began to question the validity of the selfacceptance construct and the instruments used to measure it. 1970s In the 1970s, the positive correlation between self-acceptance and acceptance of others continued to garner empirical support (e.g., Jucha, Rendecka, & Zuraw, 1979; Kawagishi, 1972). In addition, low self-acceptance continued to be associated with psychopathology (e.g., Guidano, Liotti, & Pancheri, 1971) and was also found to be associated with an external rather than internal locus of control (Chandler, 1976; Lombardo & Berzonsky, 1975). Notably, Shepard (1979) contributed a substantial multitrait-multimethod construct validation study examining self-acceptance, acceptance of others, and self-description. He found that selfacceptance had moderate construct validity, was correlated as expected with 16 / WILLIAMS AND LYNN acceptance of others, had limited discriminant validity with respect to selfdescription, and was a sensible model for “the evaluative component of the self-concept construct” (p. 139). Also of note, researchers began to describe specific stimulus domains of acceptance beyond the general categories of self and other. One prominent example was acceptance of physical disability. First measured by Linkowski (1971), acceptance of disability subsequently became a domain of study in the physical disability literature (e.g., Boone, Roessler, & Cooper, 1978; Evers, Kraaimaat, van Lankveld, Jongen, Jacobs, & Bijlsma, 2001; Groomes & Leahy, 2002; Kravetz, Faust, & David, 2000; Osuji, 1985; Starr & Heiserman, 1977). 1980s By the 1980s, acceptance, particularly self-acceptance, had been established as a useful variable in mental health theory and research, and newer lines of research began to focus on applied issues, such as self-acceptance techniques in various mental health disciplines (Baisden, Lindstrom, & Hector, 1982; Brandel, 1982; Kornblum & Anderson, 1982; Rudnick, 1982), and with specific populations (Kus, 1988; Leavy & Adams, 1986; Tenzer, 1989). Construct validation also continued apace, with further examination of self-acceptance and other constructs (e.g., Epstein & Feist, 1988; Long, 1986). The self-other correlation also continued to be examined, with more specific hypotheses, such as the finding that self-accepting men were more accepting of women in less traditional professional roles (Grube, Kleinhesselink, & Kearney, 1982). In a somewhat different vein, novel acceptance treatments began to emerge, such as Morita therapy, distinguished by less emphasis on accepting “the self” and more on accepting specific internal experiences (e.g., anxiety) as “natural objects,” for the purpose of increasing adaptive behavior (Ishiyama, 1983, p. 172; Ishiyama, 1987). 1990s The 1990s were notable for the concurrence of established lines of acceptance research and the emergence of new models of acceptance theory and treatment, most notably what we have termed experiential acceptance. The self-acceptance literature continued along established lines. The validity of the self-other correlation continued to be studied (e.g., Hurley, 1989, 1991, 1993; Hurley, Feintuch, & Mandell, 1991; Hurley & Rosenberg, 1990), as did the relationship of self-acceptance to a variety of variables, such as: psychopathology (Richter, Richter, Eisemann, & Seering, 1995), treatment outcomes (Lemberg, 1993; Weissman & Appleton, 1995), behavioral effects (Pufal-Struzik, 1998), height and intelligence (Rienzi, Scrams, & Uhles, 1992), culture and occupation (Long, 1991; Long, & Martinez, 1994), disability (Fukunishi, Koyama, & Tombimatsu, 1995; Smart & Smart, 1991), and quality of life (Rogers, 1995). Ryff (1995) included self-acceptance as one of six facets of well-being in her ACCEPTANCE: AN HISTORICAL AND CONCEPTUAL REVIEW / 17 widely used well-being scales (see Measurement of Acceptance section below). Meanwhile, Ellis (1996), reviewing his 50 years of group and individual psychotherapy, argued that because self-esteem can be maladaptive at both high and low levels, unconditional self-acceptance is a more useful construct. Still, selfesteem and self-acceptance have not yet been convincingly disambiguated. Self-acceptance research also surged in Japanese psychology journals, with scale development efforts (Itatsu, 1994, 1995; Sawazaki, 1993) and construct validation with variables derived from Western acceptance research (Ito, 1991; Makino & Tagami, 1998; Ueda, 1996). Generally, these investigations suggested some degree of cross-cultural applicability of the principles of acceptance, although this has not been examined directly. More recently, self-acceptance research has continued to refine and validate the construct (e.g., Durm & Glaze, 2001a), examine its history (e.g., Dryden & Still, 2006), and study its relationship to other variables, such as psychopathology (e.g., Scott, 2007), psychological health (e.g., Chamberlain & Haaga, 2001), self-esteem (e.g., MacInnes, 2006), mindfulness (Carson & Langer, 2006), and acceptance of others (e.g., Durm & Glaze, 2001b). A new branch of acceptance research began in the 1990s, experiential acceptance, driven in part by a convergence of mindfulness-based meditation, cognitive-behavioral interventions, and the notion that acceptance and change could be complementary therapeutic strategies. Although the body of literature that has sprung from the initial convergence is growing rapidly and includes many researchers, some noteworthy pioneers were Hayes (Hayes & Wilson, 1994), Kabat-Zinn (e.g., Kabat-Zinn, Massion, Kristeller, & Peterson, 1992), and Linehan (e.g., Linehan, Armstrong, Suarez, & Allmon, 1991), and others (e.g., Cordova, Dougher, Jacobson, Koerner, Marlatt; Hayes et al., 1994) who developed theoretical models and treatment paradigms based in part on the principles of experiential acceptance. The following section reviews some important elements of these new developments. CONTEMPORARY EXPERIENTIAL ACCEPTANCE: THEORY AND RESEARCH A variety of acceptance-based treatments have been developed and investigated for use with a range of disorders, including anxiety (e.g., Roemer & Orsillo, 2007), depression (e.g., Kanter, Baruch, & Gaynor, 2006), psychosis (e.g., Pankey & Hayes, 2003), personality disorder (e.g., Gratz & Gunderson, 2006; Linehan et al., 1991), chronic pain (e.g., McCracken & Eccleston, 2006), depressive relapse (Teasdale, Segal, Williams, Ridgeway, Soulsby, & Lau, 2000), substance abuse (Marlatt, 2002), trauma (Follette, 1994), couple discord (e.g., Jacobson, Christensen, Prince, Cordova, & Eldridge, 2000), and smoking cessation (e.g., Gifford, Kohlenberg, Hayes, Antonuccio, Piasecki, Rasmussen-Hall, et al., 2004). In addition, a host of empirical and theoretical papers have been put forth on the 18 / WILLIAMS AND LYNN relationship between acceptance and other constructs (e.g., Levy & Ebbeck, 2005; Lundh, 2004) on the integration of acceptance techniques into other therapies (e.g., Callaghan, Gregg, Marx, Kohlenberg, & Gifford, 2004; Lynn, Das, Hallquist, & Williams, 2006), and on the efficacy of acceptance-based interventions (e.g., Hayes, Luoma, Bond, Masuda, & Lillis, 2006; Hayes, Wilson, Gifford, Bissett, Piasecki, Batten, et al., 2004b; Lau & McMain, 2005; Longmore & Worrell, 2007; Roemer & Orsillo, 2002; Telford, Kralik, & Koch, 2006). In the following review, we discuss a number of conceptual and empirical components of a nascent theory of experiential acceptance: the benefits of acceptance; the development of acceptance-based treatments; the role of nonacceptance in psychopathology; the constructs of thought suppression, experiential avoidance, and emotional nonacceptance; and the paradox of acceptance and change. Benefits of Acceptance Ellis and Robb (1994) consider “unconditional self-acceptance as crucial to solid emotional and behavioral health” (p. 91). Linehan (1994) believes that moment-by-moment acceptance of the self and others is “an important part of any self-management, interpersonal effectiveness, or emotion regulation program” (p. 75). Dryden (1987, 1998) includes self-acceptance, high frustration tolerance, and acceptance of uncertainty among criteria for psychological health. Other theorists and researchers (Hayes et al., 1994; also Bond & Bunce, 2003; Greenberg & Safran, 1987) have included among the benefits of acceptance: 1. 2. 3. 4. 5. 6. expanded range of available experiences; increased potential for productive action; increased compassion and reduced blaming of others; increased compliance, serenity, and reasonableness; decreased distressing negative emotions, and positive therapeutic outcomes. Meta-analyses (e.g., Baer, 2003) and qualitative research reviews (e.g., Shapiro & Walsh, 2003) have documented the promise of acceptance and mindfulness techniques across many indices of psychological functioning. Empirically, the benefits of acceptance are often described in terms of decreased symptoms associated with acceptance-based treatment. In addition to the studies noted above, there are a number of excellent conceptual and empirical reviews that discuss acceptance-based treatments (e.g., Baer, 2006; Baer & Huss, 2008; Hayes, Follette, & Linehan, 2004c; Hayes et al., 2006; Orsillo & Roemer, 2005). In addition to symptom reduction, the benefits of acceptance in the context of mental illness can also be conceptualized in terms of other treatment goals that may occur whether or not symptom reduction takes place. These include modified beliefs about symptoms, decreased distress about symptoms, and willingness to experience symptoms while expanding adaptive behavioral repertoires. For ACCEPTANCE: AN HISTORICAL AND CONCEPTUAL REVIEW / 19 example, in recent research with acceptance-based interventions and patients with psychosis, Bach and Hayes (2002) found that patients in an Acceptance and Commitment Therapy (ACT) group showed significantly higher reporting and lower believability of psychotic symptoms (e.g., auditory hallucinations) compared to a treatment-as-usual (TAU) group. Most important, the rehospitalization rate in the ACT group was half that of the TAU group at 4-month follow-up. That is, the acceptance treatment was associated with reduced rehospitalization but not decreased symptoms (although the authors noted the possibility that the frequency of reported symptoms could have been due to a decrease in symptoms combined with a greater degree of willingness to report them). Gaudiano and Herbert (2006) replicated and extended the study, finding (in addition to equivalent symptom reporting, decreased believability, and reduced rehospitalization in the ACT condition) that the change in believability was associated with change in distress after controlling for change in frequency in the ACT group only. In a similar vein, Teasdale et al. (2002) found that increased metacognitive awareness (i.e., the extent to which aversive thoughts and feelings are experienced as mental events rather than the self) mediated the reduced relapse rates of formerly depressed patients in both mindfulness-based cognitive therapy and traditional cognitive-behavioral therapy. These findings represent key concepts in acceptance-based treatment: when stimuli (in this case, symptoms) are experienced with willingness and nonjudgment, without avoidance or struggle, in the service of valued behavioral goals, the result is a decrease in distress and maladaptive behavior. These concepts are explicated fully in Acceptance and Commitment Therapy (e.g., Hayes, Strosahl, & Wilson, 1999), the preeminent acceptance-based treatment. Treatment For half a century, acceptance has been included in humanistic-experiential therapies (e.g., Greenberg, 1994; Rogers, 1961) and Rational Emotive Therapy (Ellis, 1961; Ellis & Grieger, 1986; Ellis & Robb, 1994), generally in the form of self-acceptance. More recently, experiential acceptance has been incorporated into a number of cognitive-behavioral therapies, including: Acceptance and Commitment Therapy (Hayes & Strosahl, 2004; Hayes et al., 1999); Dialectical Behavior Therapy (Linehan,1993a, 1993b); Integrative Behavioral Couple Therapy (Jacobson & Christensen, 1996; Jacobson et al., 2000); Mindfulness-Based Cognitive Therapy (Segal, Williams, & Teasdale, 2002; Teasdale et al., 2000); and Mindfulness-Based Stress Reduction (Kabat-Zinn, 1984, 1990). Acceptance-based interventions have been developed to treat specific disorders, and syndromes, including genderalized anxiety disorder (Borkovec, Alcaine, & Behar, 2004), eating disorders (Kristeller & Hallett, 1999; Wilson, 1996), substance abuse (Hayes et al., 2004b), trichotilomania (Twohig & Woods, 2004), nicotine dependence (Gifford et al., 2004), and chronic pain (Dahl, Wilson, 20 / WILLIAMS AND LYNN & Nilsson, 2004; Kabat-Zinn, 1982; Kabat-Zinn, Lipworth & Burney, 1985; McCracken & Eccleston, 2006). Recently, a large-scale study of severely depressed people found that behavioral activation, an approach that stresses accepting depressed feelings while actively engaging in social and occupational activities, proved to be superior to a purely cognitive treatment of depression, and equal in effectiveness to pharmacological treatment (Dimidjian, Hollon, Dobson, Schmaling, Kohlenberg, Addis, et al., 2006; Dobson, Hollon, Dimidjian, Schmaling, Kohlenberg, Gallop, et al., 2008). Acceptance-based approaches have also been successfully integrated into alcohol relapse prevention programs (e.g., Marlatt, 2002), and theory suggests that they may have value in combination with hypnotic procedures (Lynn et al., 2006), in enhancing athletic performance (Gardner & Moore, 2004), and in suicide prevention (Williams & Swales, 2004). Nevertheless, it is not yet clear which aspects of these programs (e.g., exposure, enhanced expectancy, acceptance) are implicated in therapeutic changes. Acceptance and Psychopathology Conceptually, a corollary of the beneficial aspects of acceptance is that nonacceptance is associated with psychopathology. Although nonacceptance can be a problematic term because it lacks specificity, in that it may refer to a host of constructs that could be considered opposite to acceptance, such as denial, escape, prejudice, avoidance, and noncompliance, it is sometimes used to describe low levels of acceptance across a variety of behavioral and experiential domains. Ellis and Robb (1994), for example, have noted that people experience anxiety and depression when they do not accept themselves, others, and frustrating circumstances. Similarly, low experiential acceptance has been conceptualized as a contributing to or maintaining psychopathology (e.g., Hayes et al., 2004d; Strosahl, Hayes, Wilson, & Gifford, 2004). This contention finds descriptive support in the Diagnostic and Statistical Manual of Mental Disorders (DSM-IV; American Psychiatric Association, 1994), insofar as avoidance, a form of nonacceptance, is specified among the diagnostic criteria of mental disorders, including avoidant personality disorder, obsessive-compulsive disorder, phobia, posttraumatic stress disorder, and substance dependence. Analogously, attachment—a dimension of nonacceptance defined as a maladaptive attention to or pursuit of certain stimuli over others—is described indirectly in the DSM-IV in the form of preoccupations of one sort or another, as in body dysmorphic disorder; hypochondriasis; eating disorders; pathological gambling; schizophrenia, paranoid type; and narcissistic, obsessive-compulsive, and paranoid personality disorders. From a behavioral perspective, Skinner (1972) suggested that the “time and energy consumed in the avoidance of punishment” could be freed up for “more reinforcing activities” (p. 76). ACCEPTANCE: AN HISTORICAL AND CONCEPTUAL REVIEW / 21 Empirically, research areas deal with nonacceptance constructs implicated in the development and maintenance of psychopathology. These include the well researched thought suppression (e.g., Wegner et al., 1987) and experiential avoidance (e.g., Hayes et al., 1996), as well as the more recent emotional nonacceptance (e.g., Gratz, Bornovalova, Delany-Brumsey, Nick, & Lejuez, 2007; Tull & Roemer, 2007). These constructs, particularly the first two, have been reviewed elsewhere, so we will discuss them briefly. Thought Suppression Prefigured by Freud’s (1953) attention to thoughts driven from consciousness, as well as early research that instructions to suppress thoughts causes them to return (e.g., Antrobus & Singer, 1964; Langfeld, 1910), Wegner and colleagues (e.g., 1987) elaborated the paradoxical effects of thought suppression in the production and maintenance of psychological disorders. In particular, obsessivecompulsive disorder, posttraumatic stress disorder, and depression can be characterized in part by distressing, intrusive thoughts and frequent suppression attempts (Beevers, Wenzlaff, Hayes, & Scott, 1999; Purdon, 1999; Wegner, 1989; Wenzlaff & Wegner, 2000). Suppression appears to increase the frequency of the unwanted thoughts as well as intensify the emotional distress (Purdon, 1999). Wenzlaff and Wegner (2000) describe thought suppression as “a popular form of mental control . . . that it can be counterproductive, helping assure the very state of mind one had hoped to avoid” (p. 59). Although there are some inconsistencies in the literature (e.g., Purdon, 1999), many studies have documented the paradoxical effects of thought suppression. Experiential Avoidance Chawla and Ostafin (2007) describe experiential avoidance as “unwillingness to remain in contact with private experiences such as painful thoughts and emotions” (p. 871). Karekla, Forsythe, and Kelly (2004) claim that experiential avoidance is a “core psychological diathesies underlying the development and maintenance of several forms of psychopathology . . . and human suffering in general” (pp. 725-726). Blackledge and Hayes (2001) describe experiential avoidance as a focus in most systems of therapy. Freud’s (e.g., 1914/1957b) psychodynamic theory, for example, emphasizes the repression of painful or threatening material into the unconscious. In general, avoiding negative affect has been described in a variety of theories as a contributor to psychopathology (e.g., Foa, Steketee, & Young, 1984; Hayes et al., 1999; Kelly, 1955; Mowrer, 1947). Experiential avoidance can be conceptualized as comprising a number of related constructs, such as thought suppression (Wenzlaff & Wegner, 2000), emotional suppression (Gross & Levenson, 1993), avoidance coping (Penley, Tomaka, & Wiebe, 2002), reappraisal (Lazarus, 1991), and self-deception (Paulhus, 22 / WILLIAMS AND LYNN 1988). Thus, experiential avoidance may be a candidate for an organizing construct, though Chawla and Ostafin (2007) caution that it lacks theoretical integration and incremental validity relative to other constructs. Like thought suppression, avoidance is not only maladaptive, but also invokes ironic or paradoxical processes (e.g., Hayes et al., 1999). For example, not only does avoidance predispose or contribute to a variety of clinical syndromes, including depression (see MacLeod, Bjork, & Bjork, 2003; Teasdale, Segal, & Williams, 1995) and anxiety (Amir, Coles, Brigidi, & Foa, 2001), but the process of inhibiting thoughts, feelings, memories, and other internal events increases the probability that those very events will recur (Hayes & Wilson, 2003; Polivy & Herman, 1987; Strauss, Doyle, & Kreipe, 1994; Wegner et al., 1987). Both thought suppression and experiential avoidance thus appear to be associated with a rebound of unwanted content into consciousness. Emotional Nonacceptance Emotional nonacceptance has been defined as “the evaluation of emotions as bad or wrong,” leading to a “subsequent development of secondary emotional responses (e.g., fear or shame)” which may “motivate attempts to avoid emotions” (Gratz et al., 2007, p. 257). Although limited, a small body of research supports emotional nonacceptance as a factor in emotion regulation difficulties (Tull & Roemer, 2007) and anxiety disorder-related pathology (see Hayes et al., 2006; Mennin, Heimberg, Turk, & Fresco, 2005; Salters-Pedneault, Tull, & Roemer, 2004). Tull and Roemer (2007) suggest that “attempting to extinguish the emotion altogether or responding to an emotional experience with fear, shame, or some other negative emotion (secondary emotional responding or nonacceptance) is associated with worse outcomes” (p. 379). Some studies have demonstrated that the suppression of emotional expression or experience may result in increased physiological arousal (Campbell-Sills, Barlow, Brown, & Hofmann, 2006; Gross & Levenson, 1993, 1997). Prior research has shown that when emotions are suppressed or concealed, memory (Bonanno, Papa, Lalande, Westphal, & Coifman, 2004; Richards, Butler, & Gross, 2003; Richards & Gross, 1999) and problem solving (Baumeister, Bratslavsky, Muraven, & Tice, 1998) are compromised, and stress and anxiety escalate, as indexed by physiological (Richards et al., 2003, Study 2) and subjective (Levitt, Brown, Orsillo, & Barlow, 2004) markers. Acceptance and the Paradox of Change Acceptance is sometimes misunderstood to be antithetical to change. The widely quoted “Serenity Prayer” of Alcoholics Anonymous (1967), for example, can be misconstrued to mean that only what cannot be changed should be accepted. Because acceptance is not tantamount to resignation to the status quo, and efforts to change the status quo are often highly desirable (e.g., Cordova & Kohlenberg, 1994; Dougher & Hackbert, 1994), acceptance and change can ACCEPTANCE: AN HISTORICAL AND CONCEPTUAL REVIEW / 23 co-occur in at least two ways. First, if acceptance involves acknowledging the unvarnished facts of a situation rather than passivity or resignation, acceptance can occur throughout the change process. Ellis and Robb (1994) note that when one chooses change in response to a given set of circumstances, one must accept the antecedent circumstances as they are, then accept the process of change itself, and finally accept the results of the change effort. Second, acceptance itself can spur change transformation. Hayes (1994) contends that “when one gives up on trying to be different, one becomes . . . immediately different in a very profound way” (p. 20), and Greenberg (1994) holds that “the more people accept themselves in their full complexity, the more they change” (p. 55). Acceptance and change strategies have been combined in recent therapies based on mindfulness and acceptance principles, such as ACT, DBT, IBCT, MBSR, MBCT, and others. It may be that the “paradox of acceptance and change” is due in part to a misunderstanding of acceptance as well as the dialectic of acceptance and change as complementary processes. Acceptance and Mindfulness An important consideration when discussing the construct of experiential acceptance is its relation to mindful awareness or mindfulness. Bishop, Lau, Shapiro, Carlson, Anderson, Carmody, et al. (2004) recently proposed an operational definition of mindfulness that focuses on two components: sustained attention to present experience, and an attitude of openness, curiosity, and acceptance. Noting the use of the term acceptance in the definition of mindfulness, it often happens that the two constructs are discussed in tandem (e.g., “mindfulness and acceptance” research, treatments, or special interest groups), both in broad theoretical principles as well as specific interventions (e.g., Baer & Huss, 2008; Hayes et al., 2004d; Herbert & Cardaciotto, 2005; Hofmann & Asmundson, 2008; Roemer & Orsillo, 2002; Walser & Westrup, 2007). The major mindfulness interventions include an acceptance component (e.g., MBCT, MBSR), and acceptance interventions (e.g., ACT, DBT) often include informal mindfulnessbased awareness or formal mindfulness meditation training as treatment components. Finally, a number of mindfulness assessments include sets of items and factored dimensions, meant to assess acceptance. Some theorists have proposed that mindfulness is a component of acceptance (e.g., of radical acceptance; Brach, 2003), whereas others consider acceptance to be a facet of mindfulness (e.g., Baer, Smith, & Allen, 2004; Cardaciotto, 2005; Kabat-Zinn, 1994). At present there appears to be more support for the latter view, but this may reflect differential interest in the investigation of the structure of the two constructs. Whereas the structure of mindfulness is under investigation (e.g., Adele & Feldman, 2004; Baer, Smith, Hopkins, Krietemeyer, & Toney, 2006; Lau, Bishop, Segal, Buis, Anderson, Carlson, et al., 2006), the structural validation of experiential acceptance is in the early stages. The two constructs also 24 / WILLIAMS AND LYNN may be distinct but overlapping. Another difficulty is that mindfulness can refer to a theoretical construct, a psychological process, and a set of practices (Germer, 2005), which may increase the complexity of differentiating it from acceptance. ADDITIONAL FACETS OF EXPERIENTIAL ACCEPTANCE In this section we describe hypothesized facets of experiential acceptance evident in both contemporary and ancient literature which remain as yet largely speculative due to a lack of empirical scrutiny. Whenever possible, we have chosen to call these facets by the names given to them in the psychological literature. Where this is not possible or expedient, we have attempted to present each facet in a way that is reasonably coherent and faithful to a sometimes diffuse literature. We approach this task as descriptive rather than definitive. Our hope is that these considerations will contribute to the development of testable hypotheses to validate experiential acceptance more thoroughly. Awareness McCurry and Schmidt (1994) and others (e.g., Kohlenberg, 1994; Linehan, 1994; Marlatt, 1994) have observed that “awareness is basic to the acceptance process” (p. 242); in order to accept a stimulus, one first must be aware of it. Experiential acceptance may involve an ability to observe any internal or external stimulus as it is occurring, in contrast to avoidance (Hayes, 1994), suppression (Wegner, 1989), or denial (Linehan, 1994), or it may simply mean remaining “fully present” with whatever stimuli are available (Gifford, 1994, p. 220). Awareness is an area in which mindfulness and acceptance may overlap, in that mindfulness implies directed attention (Kabat-Zinn, 1990). Mindfulness has been described in fact as an “aware non-attached state of mental acceptance” (Marlatt, 1994), and may also overlap with experiential acceptance because it requires attention without evaluation, judgment, avoidance, or attachment toward any stimulus. Nonattachment The most basic definition of nonattachment in experiential acceptance may be “letting go” (e.g., Beattie, 1990), which means to release one’s attachment to internal or external stimuli (Koerner, Jacobson, & Christensen, 1994). Some classes of stimuli that have been discussed in terms of attachment and experiential acceptance include the effects of drugs or alcohol (Marlatt, 1994), one’s personal goals (Ellis & Robb, 1994), or the results of one’s efforts (Martell, Addis, & Dimidjian, 2004; Suzuki, 1973). Nonattachment can also be described in terms of constructs such as “decentering” (Segal et al., 2002, p. 41), “metacognitive awareness” (Teasdale et al., 2002), “metacognitive experiencing” ACCEPTANCE: AN HISTORICAL AND CONCEPTUAL REVIEW / 25 (Wells, 2000), and “self as context” (Strosahl et al., 2004, p. 44). Nonattachment in these constructs involves the simultaneous observation of internal or external events as they are experienced. For example, if one has the thought “I am bad,” a nonattached perspective would include an observation such as “I am having a thought that I am bad,” as opposed to an attached perspective, unable to distinguish the thought from reality. Another aspect of nonattachment is behavioral—one may accept the experience of impulses to act (e.g., to pursue or avoid stimuli) without acting on them, sometimes called nondoing (Kabat-Zinn, 1994). Nondoing can be used to distinguish nonattachment and nonavoidance, in terms of the function of a behavior. For an alcoholic, acceptance of an urge to drink may involve not walking into a bar. For a socially phobic person, however, acceptance of an impulse to avoid socializing may involve walking into the same bar. The behaviors are topographically opposite, but functionally similar: both represent nonattachment to private urges. Another way of considering the relationship between attachment and avoidance is that avoidance tends to be negatively reinforced through the removal of an aversive stimulus, whereas attachment tends to be positively reinforced through the addition or maintenance of an appetitive stimulus. Nonjudgment Nonjudgment is central to modern conceptualizations of acceptance (e.g., Cordova & Kohlenberg, 1994, Germer, 2005; Hayes, 2004a; Hayes & Wilson, 2003; Peterson, 1994) as well as mindfulness (Baer et al., 2006; Dimidjian & Linehan, 2003; Kabat-Zinn, 1994; Kohlenberg, 1994; Linehan, 1993a). Nonjudgment is a conscious abstention from categorizing experience as good or bad (Cordova & Kohlenberg, 1994), or right or wrong (Hayes, 1994; Linehan, 1994), such as “anxiety is bad.” Nonjudgment is included in a number of cognitivebehavioral therapies that employ mindfulness and acceptance (e.g., ACT, DBT, MBCT), as well as older therapies such as Rational Emotive Behavior Therapy (REBT; David, Lynn, & Ellis, 2009; Ellis & Dryden, 1997). According to REBT, beliefs mediate the emotional consequence of an activating event, and to that extent judgments determine experience. Highly negative evaluation of internal or external events has been characterized as “awfulizing” and catastrophizing, which may potentiate anxiety and depression (Beck, Emery, & Greenberg, 1996; Ellis & Robb, 1994), and the expectation of negative events or their continuing without relief can have serious negative consequences (see Abramson, Alloy, & Hogan, 1997; Kirsch & Lynn, 1995). Nonjudgment in experiential acceptance involves actively processing stimuli according to their descriptive or concrete properties rather than evaluating them. Radical Acceptance Some theorists use the term radical acceptance to describe a Zen-like state of acceptance, consisting of a thorough willingness to experience whatever is taking 26 / WILLIAMS AND LYNN place in the moment (e.g., Brach, 2003; Linehan, 1994). Radical acceptance may be the positive extreme of experiential acceptance, in which, according to Linehan (1994), one experiences “total allowance now,” and a “constant accepting in each successive moment” (p. 80). As noted above, in the classical literature acceptance is associated with wisdom and enlightenment, which can be profound and paradoxical. In a similar vein, some modern authors (e.g., Robbins, Schmidt, & Linehan, 2004) have noted paradoxical effects of radical acceptance. Fruzzetti and Iverson (2004) hold that by radically accepting a stimulus one has experienced as negative, the valence of the stimulus may be reversed so that it not only loses its aversive quality but acquires appetitive properties. It is possible to imagine, for example, a person who is phobic of snakes subsequently coming to own and enjoy them. Tolerance Whether tolerance should be considered an aspect of acceptance has been the subject of some debate. For example, Fruzzetti and Iverson (2004) describe acceptance as inclusive of “simple tolerance” (p. 177), but Hayes and colleagues (2004a) assert that acceptance should not be equated with tolerance or resignation. Some authors, such as Linehan (1994) and McCurry (1994), take issue with the word tolerance itself, based on its association with stoical austerity, though Ellis and Robb (1994) note, in fact, that elements of stoic philosophy were key ingredients in the development of Rational Emotive Behavior Therapy. Tolerance need not connote helpless resignation, as its etymological roots can be found in a variety of verbs such as endure, permit, allow, indulge, bear, and carry (Onions, 1966, p. 929). These roots contribute to three modern denotations of tolerance (Weiner & Simpson, 1991, p. 2075) . First, as an ability to endure pain or hardship, acceptance may include an ability to tolerate emotional distress (e.g., Afari, 1994; Cordova & Kohlenberg, 1994; Fruzzetti & Iverson, 2004; Linehan, 1994; Wulfert, 1994), especially when such tolerance takes the place of maladaptive behaviors or in the service of one’s values (Hayes & Strosahl, 2004). Tolerance can represent an ability to endure the moment, even if the moment is unpleasant and one intends to improve it. Second, as a disposition to be patient with the opinions or practices of others, including a freedom from bigotry or undue severity in judging others, tolerance is consistent with acceptance of others (e.g., Ellis & Robb, 1994; Fruzzetti & Iverson, 2004; Gandhi, 1999; Greenberg, 1994; Linehan, 1994). Third, tolerance is consistent with behavioral principles, such as habituation, an acquired ability to experience a stimulus based on repeated exposure, and exposure therapy (e.g., McAllister & McAllister, 1995; O’Donohue & Krasner, 1995), in which repeated contact with a stimulus results in a decrease in arousal and an expansion of the behavioral repertoire. Tolerance then may be built up toward specific stimuli, such as one’s own emotions or the situations that engender them. Altogether, these ACCEPTANCE: AN HISTORICAL AND CONCEPTUAL REVIEW / 27 definitions are consistent with theorists who characterize experiential acceptance as an ability to experience stimuli without resorting to avoidance or escape. Willingness Willingness is represented in the acceptance literature as a disposition to undertake an action or consent to an experience. Germer (2005) defined acceptance as a willingness is to “let things be just as they are the moment we become aware of them, accepting pleasurable and painful experiences as they arise” (p. 7). For Wulfert (1994) acceptance is the willingness “to face difficult situations and tolerate whatever feelings come up” (p. 215). Marlatt (1994) describes the willingness to “surf” urges rather than abuse substances: clients are instructed to “let go” and “allow the urge to rise and fall on its own” (p. 181). Willingness, then, is often associated with enacting a new, adaptive, behavior while tolerating the discomfort associated with the change. In ACT (Hayes et al., 1999), for example, substantial attention is given to developing new behavioral repertoires, and taking action in accordance with valued goals. More generally, a patient who follows a mental health professional’s instructions practices willingness in the sense of treatment adherence. Domains of Acceptance Stimulus domains define the objects of acceptance, or what is accepted when acceptance takes place. The objects of experiential acceptance may comprise whatever stimuli are present, though historically the acceptance literature has specified two primary domains: “self-acceptance” (e.g., Berger, 1952; Ellis & Dryden, 1997; Maslow, 1954; Rogers, 1961) and “acceptance of others” (e.g., Ellis & Robb, 1994; Fey, 1954, 1955; Greenberg, 1994; Phillips, 1951). As discussed above, the self and other domains have been substantially validated over the years and also have been shown to be correlated (e.g., Berger, 1952; Omwake, 1954; Suinn & Geiger, 1965; Trent, 1957). They also point to two, more general, categories which together also would include all of the relevant stimulus domains pertaining to experiential acceptance. These can be termed internal and external, with internal referring to private experience, or stimuli occurring within the self, and external referring to all stimuli occurring outside the self. Internal stimuli have been conceptualized as comprising at least three types of stimuli: 1. thoughts (e.g., Hayes, 1994; Kornfield, 1993); 2. feelings (e.g., Ellis & Robb, 1994; Hayes, 1994; Martell et al., 2004; Rogers, 1961); and 3. sensations (e.g., Hayes, 1994; Kornfield, 1993; Marlatt, 1994; McCracken, 1998), as well as complex events stemming from the interaction of these three basic domains. 28 / WILLIAMS AND LYNN External stimuli associated with acceptance have been defined mainly with respect to two types of stimuli: other people and situations. Together, internal and external acceptance would appear to cover most domains of experience. Within the domains of internal and external, however, there are more possible classes of stimuli beyond the five sub-domains listed here (e.g., pain is a specific stimulus domain associated with unique treatment paradigms and measurement instruments within the acceptance literature). Measurement of Acceptance Classic Self-Acceptance Scales of the 1950s Scales designed to measure acceptance have developed over the years along with emerging conceptualizations of the construct. Early measures of acceptance were developed in the 1950s based on contemporary conceptualizations of selfacceptance and acceptance of others, drawing on theorists such as Adler, Ellis, Horney, Fromm, Perls, Rogers, and Sullivan. In general, acceptance in these measures was operationalized as a positive attitude toward the self and others. Although at least eight acceptance measures were developed in the 1950s (see Crowne & Stephens, 1961), only four were used widely: Berger’s (1952) Expressed Acceptance of Self and Others Scale, Bills’ (1958; Bills, Vance, & McLean, 1951) Index of Adjustment and Values, Fey’s (1954) Acceptance of Self and Others Scale, and Phillips’ (1951) Self-Others Questionnaire, each of which accumulated some degree of reliability and validity data (Fey, 1955; Omwake, 1954; Sheerer, 1949). These measures were used in studies supportive of a number of hypotheses about acceptance, including the prediction that selfacceptance and acceptance of others were positively correlated, that acceptance was negatively correlated with psychopathology, and that measures of acceptance tended to converge on a single construct. Within a decade of the development of these measures, however, a number of investigators began to question the validity of the self-acceptance construct and the instruments used to measure it, on conceptual and methodological grounds. The major criticisms were that the construct was poorly defined, varying substantially across researchers and theorists, and that the instruments were conceptually unsound, poorly constructed, and confounded with social desirability (e.g., Block & Thomas, 1955; Crowne & Marlowe, 1964; Crowne & Stephens, 1961; Kinkler & Myers; 1963; Stone, 1964). Although only a few acceptance scales were used much beyond the studies in which they were developed—the rest being constructed for a specific research purpose and never again cited— the critics of acceptance measures tended to review them together. Some scales, however, received relatively more validation over time than others. Berger’s (1952) scale has received the widest use and most thorough validation. Composed of 64 items (36 self-acceptance and 28 acceptance of others), ACCEPTANCE: AN HISTORICAL AND CONCEPTUAL REVIEW / 29 self-acceptance and acceptance of others were operationalized on 16 behavioral dimensions, largely based on Sheerer’s (1949) “acceptance and respect” for oneself and others (p. 170). The scale was initially validated on a combined school, community, prison, and clinical sample of 315 subjects. The scale showed good reliability (.75–.89 for self-acceptance; .78–.88 for other acceptance) and initial validity based on expected correlations between the self and other item sets (.36–.69 across samples) and expected correlations with free writing tasks rated for degree of acceptance (.78–.90). Early uses of the scale included testing the relationship between self and other acceptance, and between acceptance and psychopathology (Berger, 1952, 1955). Because the Berger scale has the largest body of research of any scale of that era, it is a useful reference for a host of established construct relations. In addition, it includes both self and other scales, which may be used alone or in combination. The main weakness of the Berger scale concerns the extent to which it measures acceptance, as opposed to social desirability or, for that matter, self-esteem (e.g., Antill & Cunningham, 1979; Eagly & Whitehead, 1972; Neff, Kirkpatrick, & Rude, 2007). Nevertheless, the Berger scale may be considered the measure of choice among the original acceptance scales from the 1950s. Unconditional Self-Acceptance Questionnaire (USAQ) The USAQ (Chamberlain & Haaga, 2001) was designed to operationalize self-acceptance consistent with the principles of Rational Emotive Behavior Therapy (REBT; Ellis, 1973; Ellis & Dryden, 1997). It was constructed to differentiate self-acceptance from self-esteem, although it has shown a substantial correlation with self-esteem, and the nature of the relationship between the two constructs remains under investigation (e.g., Chamberlain & Haaga 2001; MacInnes, 2006; Thompson & Waltz, 2008). Relatedly, the USAQ is the only scale that specifically addresses unconditional self-acceptance as distinct from positive self-regard. The USAQ is also the only recent self-acceptance scale constructed as a stand-alone measure, rather than as a component of another construct, such as well-being. Despite these strengths, the major drawback of the USAQ is that it is a relatively new scale with a good reliability profile but limited construct validity data. Self-Acceptance Subscales of Multitrait Measures Personal Orientation Inventory (POI; Knapp, 1976; Shostrom, 1964, 1966)— The POI is a 120-item inventory of psychological well-being, mental health, and self-actualization with substantial evidence of validity (Fox, Knapp, & Michael, 1968; Hattie, 1986; Shostrom, 1964). The POI includes twelve scales, three of which are relevant to acceptance: self-acceptance, self-regard, and acceptance of aggression. A strength of this scale is its substantial reliability and validity, supported by a host of studies over the last 50 years. Another apparent strength is 30 / WILLIAMS AND LYNN the inclusion of multiple acceptance-related scales, and the intentional differentiation between self-acceptance and self-regard. That said, although the selfregard and self-acceptance scales generally correlate in the .20 range (Shostrom, 1973), Shepard (1979) was unable to distinguish the two scales at the item level, and other studies have suggested that fewer dimensions overall may be more parsimonious (e.g., Klavetter & Mogar, 1967). Further, although the selfacceptance and self-regard scales were used in the major construct validation of the self-acceptance construct to date (Shepard, 1979), few studies have reported the reliability and validity of the self-acceptance subscale alone. California Psychological Inventory (CPI; Gough, 1957, 1987)—The CPI is a 434-item assessment of normal personality (Gough, 1957; Gough & Bradley, 1996). A 260-item shorter version is also available. The CPI has a research base of approximately 2,000 citations, and is based on a normative sample of 6,000 men and women (see Gough & Bradley, 1996). The CPI includes 29 subscales. The Self-Acceptance subscale measures “sense of personal worth, self-acceptance, and capacity for independent thinking and action; being secure with and sure of oneself” (Megargee, 1972, p. 67). The CPI also includes a Tolerance subscale, which measures “permissive, accepting, and nonjudgmental social beliefs and attitudes” (p. 91). Like the POI, a major strength of the CPI is its established reliability and validity. Also like the POI, however, the body of research supportive of the CPI relates to the scale as a whole rather than individual subscales. Although the CPI has been used in a number of acceptance studies (e.g., Ganter, 1962; Greene, Baucom, & Macon, 1980), few studies have reported reliability and validity data for the self-acceptance subscale, with the exception of Vingoe (1968). Additionally, factor analytic studies generally have not found structural evidence of a self-acceptance factor (Crites, Bechtoldt, Goodstein, & Heilbrun, 1961; Mitchell & Pierce-Jones, 1960; Nichols & Schnell, 1963; Pumroy, 1962; Springob & Struening, 1964). Scales of Psychological Well-Being (SPW; Ryff, 1995)—The SPW is an 84-item scale of psychological well-being composed of six 14-item scales constructed to measure the dimensions of autonomy, environmental mastery, personal growth, positive relations with others, purpose in life, and self-acceptance. The reliability and validity of the SPW were demonstrated in the original development studies and follow-up appraisals (e.g., Ryff, 1989, 1995; Ryff & Keyes, 1995; Ryff & Singer, 2006). Self-acceptance is included among those dimensions that “encompass a breadth of wellness that includes positive evaluations of oneself and one’s past life” (Ryff, 1995, p. 720). The Self-Acceptance scale is operationalized as follows. A high scorer “possesses a positive attitude toward the self; acknowledges and accepts multiple aspects of self, including good and bad qualities; feels positive about past life” (p. 727). Measures of happiness show modest to strong associations with the Self-Acceptance scale (Ryff, 1995). Based on the validation of its six-factor model, the SPW may be considered a ACCEPTANCE: AN HISTORICAL AND CONCEPTUAL REVIEW / 31 primary measure of psychological well-being. The major strength of this scale is its substantial reliability, validity, and corpus of construct relations established. Its major weakness is the limited reliability of the Self-Acceptance scale (a = .46). Experiential Acceptance Scales Acceptance and Action Questionnaire (AAQ) A variety of new instruments have been developed that operationalize experiential acceptance. The AAQ (Hayes et al., 2004a) was developed to measure acceptance, operationalized primarily as experiential avoidance. It was validated initially on 10 samples collected during separate investigations of experiential avoidance. A 32-item version of the scale was developed using an item pool based on the theory of experiential avoidance employed in ACT, in which experiential avoidance was defined as “the phenomenon that occurs when a person is unwilling to remain in contact with particular private experiences . . . and takes steps to alter the form or frequency of these experiences and the contexts that occasion them, even when these forms of avoidance cause behavioral harm” (p. 554). The AAQ has a substantial research base, having been used in at least 70 studies investigating the role of experiential acceptance in clinical disorders, such as anxiety (e.g., Tull & Roemer, 2007), depression, (e.g., Cribb, Moulds, & Carter, 2006), and personality (e.g., Gratz, Rosenthal, Tull, Lejuez, & Gunderson, 2006), as well as general psychological vulnerability (e.g., Kashdan, Barrios, Forsyth, & Steger, 2006), well-being (e.g., Kashdan & Breen, 2007), job performance (e.g., Bond & Flaxman, 2006), and pain tolerance (Feldner, Hekmat, Zvolensky, Vowles, Secrist, & Leen-Feldner, 2006). The AAQ has also been instrumental in the development of other scales (e.g., Baer et al., 2004; Gratz & Roemer, 2004; McCracken, Vowles, & Eccleston, 2004). A number of versions of the scale are in use at present, with 9, 10, and 16 items, as well as the initial 49-item pool, sometimes used in factor analytic studies (R. Baer, personal communication, 2006). The AAQ is generally considered to be composed of one general factor of experiential avoidance, or conversely experiential acceptance with reverse coding (e.g., Hayes et al., 2004a). That said, the AAQ appears to operationalize, in adition to nonavoidance of aversive stimuli, facets reflecting willingness to experience unpleasant emotions and a capacity for productive action in the face of those stimuli and emotions. The AAQ may be considered the current gold standard measure of experiential acceptance. Nevertheless, the factor structure has not yet been resolved, due in part to the fact that there are a number of versions of the AAQ in use. Additionally, the internal consistency has not always been optimal. These issues, however, may be resolved when the revised AAQ (AAQ-R) is published. Although the factor structure may include dimensions associated with willingness and action, the AAQ was constructed to measure experiential avoidance, and may therefore measure only one dimension of acceptance. 32 / WILLIAMS AND LYNN Other Avoidance Scales In addition to the AAQ, there are a number of other measures that have been used to measure and validate various types of avoidance, including: the Cognitive-Behavioral Avoidance Scale (CBAS; Ottenbreit & Dobson, 2004), which measures avoidance across several dimensions, including cognitive versus behavioral avoidance, active versus passive avoidance, and social versus nonsocial avoidance; the White Bear Suppression Inventory (WBSI; Wegner & Zanakos, 1994), which measures the tendency to suppress unwanted thoughts; the Thought Control Questionnaire (TCQ; Wells & Davies, 1994), which measures the specific strategies used to control unpleasant or unwanted thoughts; and the Escape-Avoidance subscale of the Ways of Coping Questionnaire (WCQ; Folkman & Lazarus, 1988), which measures coping characterized by escape and avoidance, such as wishing a situation would go away, or by eating, drinking, smoking, or using drugs to feel better. The CBAS, WBSI, TCQ, and WCQ represent some of the core instruments that have been used to operationalize and validate the construct of avoidance, and have also shown moderate correlations with the AAQ. Experiential Acceptance Subscales in Multidimensional Measures Similar to self-acceptance, experiential acceptance also has been included as a factor in multidimensional measures. In some cases, acceptance skills are conceptualized as components of larger skill sets. The Difficulties in Emotion Regulation Scale (DERS; Gratz & Roemer, 2004) includes an Emotional Nonacceptance (EN) factor of items reflecting “a tendency to have negative secondary emotional responses to one’s negative emotions, or nonaccepting reactions to one’s distress” (p. 47). The DERS operationalizes emotion regulation as involving awareness, understanding, and acceptance of emotions, and the inclusion of the EN factor is based on the theory that a lack of emotional acceptance is maladaptive and associated with greater difficulties in emotion regulation. In a similar vein, the COPE scales (COPE; Carver, Scheier, & Weintraub, 1989), a general measure of coping, include an Acceptance factor composed of items assessing the degree to which a person can: a) accept the existence of stressors, and b) accept the limits of his or her own coping strategies. The COPE operationalizes acceptance as the opposite of denial and assesses coping in part as the ability to attempt to deal directly with stressors even when one’s coping skills are inadequate. A shorter version of the COPE, the Brief COPE (BC; Carver, 1997) retains acceptance items. Domain-Specific Acceptance Scales A number of scales assess acceptance within specific stimulus domains, or item content categories including acceptance of: athletic performance (Sport-Specific ACCEPTANCE: AN HISTORICAL AND CONCEPTUAL REVIEW / 33 Self-Acceptance Scale; SSS; Waite, Gansneder, & Rotella, 1990), death (Death Acceptance Scale; DAS; Ray & Najman, 1974), disability (Acceptance of Disability Scale; ADS; Linkowski, 1971), illness (Acceptance of Illness Scale; AIS; Felton, Revenson, & Hinrichsen, 1984), and romantic partners (Frequency and Acceptability of Partner Behavior Inventory; FAPBI; Doss & Christensen, 2006). The way acceptance is operationalized is not necessarily uniform across these measures, although a number of domain-specific scales have been closely patterned on the AAQ. These include scales assessing acceptance of auditory hallucinations (Voices Acceptance and Action Scale; VAAS; Shawyer, Ratcliff, Mackinnon, Farhall, Hayes, & Copolov, 2007) and chronic pain (Chronic Pain Acceptance Questionnaire; CPAQ; McCracken et al., 2004), and scales currently in development, including acceptance of diabetes, epilepsy, smoking, and tinnitus (S. C. Hayes, personal communication, August 2, 2005). Most acceptance scales are in fact specific to only one or two domains and dimensions. The AAQ, for example employs thoughts and feelings as stimulus domains and operationalizes acceptance as nonavoidance. In contrast, the classic self-acceptance measures employ domains of self and other and operationalize acceptance along the dimension of positive regard. If acceptance is a multidimensional construct, no extant scale can be considered a truly general measure of acceptance necessary to establish further structural validity. Measurement of Related Constructs Measures of Mindfulness In the past decade, a number of measures have been developed to assess mindful awareness. These measures differ somewhat in their operationalization and use. For example, the Kentucky Inventory of Mindfulness Skills (KIMS; Baer et al., 2004) is based on mindfulness skills taught in Dialectical Behavior Therapy (DBT; Linehan, 1994) and was designed to measure mindfulness in the general population. In contrast, the Freiburg Mindfulness Inventory (FMI; Walach, Buchheld, Buttenmüller, Kleinknecht, & Schmidt, 2006) is based on Vipassana principles and was designed to measures changes in mindfulness in meditators over the course an ongoing practice. Similarly, the Toronto Mindfulness Scale (TMS; Lau et al., 2006) was designed as a state measure of mindfulness, for use immediately following a meditation session. The Cognitive and Affective Mindfulness Scale–Revised (CMS-R; Feldman, Hayes, Kumar, Greeson, & Laurenceau, 2007), based on contemporary mindfulness theory, is a multi-dimensional scale that appears to measure changes in mindfulness over the course of psychotherapy. In contrast, the Mindful Awareness and Attention Scale (MAAS; Brown & Ryan, 2003) and Mindfulness Questionnaire (MQ; Chadwick, Hember, Mead, Lilley, & Dagnan, 2005; see Baer et al., 2006) assess single dimensions of mindfulness, respectively, present attention and awareness, and a mindful approach to distressing thoughts and images. Other 34 / WILLIAMS AND LYNN scales have been validated initially, such as Philadelphia Mindfulness Scale (PHLMS; Cardaciotto, 2005; Cardaciotto & Herbert, 2005), a two-factor scale measuring awareness and acceptance. One noteworthy scale has resulted from a factor-analytic study of five mindfulness scales (CAMS, FMI, KIMS, MAAS, and MQ) by Baer and colleagues (2006). This Five-Factor Mindfulness Questionnaire (FFMQ) has provided evidence for the structural validity of mindfulness as measured by the KIMS scale: items from the five measures appear to map onto the KIMS four-factor structure (Observe, Describe, Act With Awareness, Accept Without Judgment) with the addition of one additional factor (Nonreactivity). Although it will require further validation, the FFMQ appears to be a useful instrument for construct validation of mindfulness and acceptance. The psychometric properties and validity of these measures have been described in detail elsewhere (see Baer et al., 2006; Block-Lerner et al., 2005), including their correlations with acceptance scales (e.g., the KIMS accept dimension has shown a –.26* correlation with the AAQ; Baer et al., 2004). However, most of these scales operationalize mindfulness in ways that overlap with acceptance. For example, the FMI used acceptance-like facets to construct items reflecting nonjudgment toward the self and others, and openness to positive and negative sensations. Other scales include distinct acceptance dimensions with subsequent validation by factor analysis, such as the CAMS (Acceptance of Internal Experiences factor), the KIMS and FFMQ (Accept without Judgment factor), the PHLMS (Acceptance factor), and the TMS (Observation factor, composed of curiosity, acceptance, and openness to experience). In contrast, the MAAS was constructed to assess only attention to and awareness of what is occurring in the present, and not “attributes such as acceptance, trust, empathy, gratitude, or the various others that have been associated with mindfulness” (Brown & Ryan, 2003, p. 824). As a result, MAAS items contain no obvious acceptance content. It may be the case that the MAAS may be considered the purest measure of mindfulness with respect to acceptance content, although it should be noted that the MAAS was significantly correlated with the KIMS accept without judgment factor at .30* (Baer et al., 2004). Scales Measuring Hypothesized Acceptance Dimensions We consider here a number of measures that may operationalize some of the remaining dimensions of experiential acceptance in the literature. One scale that may assess nonattachment is the Experiences Questionnaire (EQ; Fresco, Moore, van Dulmen, Segal, Ma, Teasdale, et al., 2007), which measures decentering; specifically, “the ability to observe one’s thoughts and feelings as temporary, objective events in the mind, as opposed to reflections of the self that are necessarily true” (p. 234). Another is the Nonattachment Scale (NAS; Hoffman, 2007), a measure of Buddhist nonattachment across four domains: attachment, ACCEPTANCE: AN HISTORICAL AND CONCEPTUAL REVIEW / 35 wisdom, morality, and mindfulness. Both the EQ and NAS are new scales, but with further validation each may be a useful addition to the complement of measures available to validate the structure of experiential acceptance. Distress tolerance is a common construct in the affect dysregulation literature, and the Distress Tolerance Scale (DTS; Simons & Gaher, 2005) assesses “the capacity to experience and withstand negative psychological states” (p. 83). The DTS fits a single factor model in the initial validation study, though it was developed to address four domains: tolerance of emotional distress, subjective appraisal of distress, absorption in negative emotion, and attempts at regulation. The DTS may also be a useful measure in the validation of acceptance. CONCLUSIONS AND FUTURE DIRECTIONS Our survey has revealed that the term acceptance has been established across a wide range of disciplines, and that even within clinical science it has been conceptualized broadly. Self-acceptance has been considered a component of psychological health since it was first described a century ago, and this contention has found support in subsequent empirical investigation. For example, higher self-acceptance is associated with lower levels of psychopathology, validated with host of studies using multiple methods measuring a spectrum of psychopathology. Additionally, self-acceptance correlates positively with measures of adjustment, well-being, satisfying interpersonal relationships, affect regulation, and other correlates of mental health. Another well established relation is the positive correlation between self-acceptance and acceptance of others (note, however, that being self-accepting does not correlate with being accepted by others). One area of further study includes examining the divergence of self-acceptance definitions: some conceptualizations and measurement instruments are closer to nonjudgmental self-awareness, others to unconditional positive self-regard, and still others to self-esteem. Experiential acceptance appears to be negatively related to psychopathology, and constructs integral to the development and maintenance of psychopathology (e.g., thought suppression, experiential avoidance, and emotional nonacceptance) can be defined more generally as nonacceptance. In addition, experiential acceptance appears to be positively related to emotional regulation, frustration tolerance, well-being, and other indicators of mental health. Accordingly, acceptance-based interventions have been efficacious in treating a wide range of problems (e.g., mental disorders, marital discord, pain syndromes), and specific interventions have been developed for a growing number of conditions and populations. Treatment packages, such as ACT and DBT, have a substantial base of efficacy research and often serve as the model upon which the more targeted interventions are based. Nevertheless, additional trials are necessary to evaluate the role of exposure as well as placebo and nonspecific effects in these treatments. 36 / WILLIAMS AND LYNN Our review has raised important issues related to the construct validity of experiential acceptance, which may be of interest as areas for future research. The first issue relates to content validity. Classical, modern, and contemporary conceptualizations vary in the inclusion, exclusion, and emphasis of the hypothesized facets we have described (e.g., nonavoidance, nonjudgment, selfacceptance), and acceptance measures differ in the way the construct is operationalized. Relatedly, the structural validity of acceptance also remains to be investigated. Indeed, no single measure captures acceptance as broadly as it has been explicated in the literature. The second issue relates to convergent validity. It is not clear, for example, whether contemporary conceptualizations of acceptance are distinct from earlier notions of self and other acceptance. Although they appear to diverge theoretically (e.g., positive self-regard vs. nonavoidance), this has not been investigated. Relatedly, there are a growing number of new acceptance measures; however, the extent to which they converge on a single construct or show incremental validity with respect to existing measures remains to be determined. The third question relates to discriminant validity. It is difficult to disambiguate experiential acceptance from other constructs, particularly mindfulness, although the structural validity of mindfulness has received the most attention (e.g., Baer, Smith, & Allen, 2004; Baer, et al., 2006). Thus it is difficult to say, for example, which facets of acceptance reviewed belong to which construct, or if there may be a unifying construct present. Moreover, although mindfulness and acceptance can be cultivated, there may be significant innate differences among people that vary in terms of temperament and attentional style. The genesis of individual differences, including why some people are more tolerant of painful emotions than others, remains largely unexplored. More refined and inclusive measures of acceptance will help investigators to address the nature, extent, and determinants of individual differences, and assist researchers in addressing the following questions related to psychotherapy and personal change: Do some dimensions of acceptance account for more robust changes than other dimensions across diverse psychotherapies? Are some aspects of acceptance (e.g., self-acceptance) non-specific ingredients of effective psychotherapy, or do some dimensions of acceptance produce more specific or perdurable treatment effects? And, finally, how can we strive for goals while maintaining a present-centered, accepting mindset? We have much to learn about the flip-side of acceptance—nonacceptance; in particular, its relationship with psychopathology through escape from experiences, and the resulting negative effects through ironic processes. An important question is whether the causal arrow points in the other direction, such that psychopathology engenders a lack of acceptance of self and others, attempts to suppress distressing emotions, and a failure to attend to moment-to-moment experience. In all likelihood, there is a recursive relation between psychopathology and acceptance, although this has yet to be established. The question of the ACCEPTANCE: AN HISTORICAL AND CONCEPTUAL REVIEW / 37 relation between nonacceptance and measures of general psychopathology, trait neuroticism, and depression are also in need of empirical attention. The paradoxical effects of acceptance are not well understood. Perhaps the very idea that we can tolerate emotionally painful experiences bolsters hope, expectations for change and positive outcomes, independent of the effects of habituation of fears or dysphoria by way of exposure. When we appraise cognitions as merely “thoughts,” we may well curtail the tendency to catastrophize or distort thinking, and thereby experience relief from anxiety and depression. Enhanced awareness of maladaptive thought patterns and attachments to habitual ways of thinking may afford awareness of early indicators of maladaptive responses (Baer, 2003; Linehan, 1993a, 1993b; Marlatt, 1994) and tendencies to relapse from disorders such as depression (Teasdale et al., 1995), thereby establishing an “early warning system” (Lynn et al., 2006). Clearly, there is much room for theory development and models that link different dimensions with measurable psychological and health-related outcomes, and with well-established psychological principles (e.g., exposure) of behavior change. In closing, although there have been substantial advances in the development of acceptance as a clinical intervention, much work remains to be done with respect to the construct. The current status of the acceptance literature in fact suggests that the time is not yet ripe for an integrative model of acceptance. The acceptance-based treatments that can be subsumed under cognitive-behavioral theory are quite new, and the terms used to describe acceptance (e.g., nonavoidance, willingness, etc.) have been used rather loosely. Even ACT, which is arguably the most fully developed acceptance treatment, has only recently begun to describe how acceptance and mindfulness relate to one another (possibly, the former is a component process of the latter; Baer et al., 2006). Acceptance researchers do not appear yet to have gathered enough evidence to support one factor solution over another. In short, it may be too soon to determine the extent to which all of the various conceptualizations (e.g., ACT, DBT, MBSR, etc.) overlap or converge on a single construct. That said, the systematic study of acceptance can contribute to our understanding of different psychotherapies, the genesis and maintenance of psychological disorders, and the mechanisms and processes that facilitate and impede personal change. From its early roots in Buddhist, Hindu, and Taoist writings, to more contemporary scholarly works from a literary, philosophical, and scientific perspective, acceptance is an idea whose time has come. 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