Josef MattesFakultät für Mathematik, Universität Wien, Vienna, Austria,

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Parallels between the ancient Hellenistic philosophies of the Stoics and Epicureans, on the one hand, and modern cognitive psychotherapy, on the other, are well known and a topic of current discussion. The present article argues that there are also important parallels between Pyrrhonism, the third of the major Hellenistic philosophies, and the currently state-of-the-art “3rd wave” cognitive-behavioral therapies in general, and Acceptance and Commitment Therapy (act) in particular. This provides a crucial insight into Pyrrhonism: understanding Sextus’ term adoxastos using the technical act term ‘defusion’ illuminates the psychological condition of the Pyrrhonist and explains why the apraxia objection against Pyrrhonism is misguided.


Parallels between the ancient Hellenistic philosophies of the Stoics and Epicureans, on the one hand, and modern cognitive psychotherapy, on the other, are well known and a topic of current discussion. The present article argues that there are also important parallels between Pyrrhonism, the third of the major Hellenistic philosophies, and the currently state-of-the-art “3rd wave” cognitive-behavioral therapies in general, and Acceptance and Commitment Therapy (act) in particular. This provides a crucial insight into Pyrrhonism: understanding Sextus’ term adoxastos using the technical act term ‘defusion’ illuminates the psychological condition of the Pyrrhonist and explains why the apraxia objection against Pyrrhonism is misguided.

1 Introduction

Parallels between the ancient Hellenistic philosophies of the Stoics and Epicureans, on the one hand, and modern cognitive psychotherapy, on the other, are well known and a topic of current discussion. Neglected in these discussions is the third of the major philosophical ways of life that originated in Hellenistic times: that named after Pyrrho of Elis and expounded in the works of Sextus Empiricus. The present essay argues, first, that there are important parallels between this Pyrrhonian Way and the currently state-of-the-art “3rd wave” cognitive-behavioral therapies, especially Acceptance and Commitment Therapy (act); and second, that this provides crucial insight into the Pyrrhonian Way in general, and the so-called apraxia objection in particular.

The paper is organized as follows. Section 2 gives a brief overview of the relevant aspects of the Pyrrhonian Way. Section 3 summarizes some of the major objections to it, including the apraxia objection. Section 4 provides some background concerning the relationship between ancient philosophy and psychotherapy. Section 5 gives a brief overview of act. After these preparatory parts, Section 6 relates the Pyrrhonian Way to act. Sections 7, 8, and 9 comprise the discussion, respectively focusing on whether the Pyrrhonian Way enables one to lead a good life, on whether (or to what extent) the Pyrrhonist has a “life without belief,” and on the apraxia objection. Finally, Section 10 concludes and acknowledges some limitations of the present work.

2 The Pyrrhonian Way

Despite being little known outside specialist academic circles, the work of Sextus Empiricus seems of remarkable interest not only to philosophy more widely, but also to psychology. On the one hand, his work may well be, in the history of western philosophy, the third most influential among ancient Greek philosophers (Mates 1996: 4; Popkin 1979), with only those of Plato and Aristotle ahead of his. On the other hand, he made claims about achieving tranquility by following the Pyrrhonian Way (named after the earlier Hellenistic philosopher Pyrrho1) which should be of interest to psychologists and psychotherapists, since “if […] it turns out that the Pyrrhonists found a way to secure peace of mind, we better know the details” (Wieland 2012: 277). Except for the work of Sextus, hardly any information about the Pyrrhonian Way has survived (see Decleva Caizzi 2020 for the surviving fragments related to Pyrrho), therefore his extant works (ph, ad, am)2 have been extensively studied by philosophers. Nevertheless, I am not aware of any work approaching him from the point of view of psychological science, despite philosophers not being shy to make psychological pronouncements concerning his work, and despite his obvious (at least potential) relevance to positive psychology and psychotherapy.

In this essay, I use the terminology “Pyrrhonian Way” rather than the more common terms Pyrrhonism or Skepticism because it is clear that Sextus did not want to propagate yet another -ism (Mates 1996: 6; Jürß 2001: 7), and because he “frequently uses the word agōgē (“way of life,” “conduct”) to describe his own stance” (Marchand 2019: 25). In particular, I will avoid the term “skepticism,” the reason being that today it has connotations that are very different from the meaning of the Greek word skepsis.

According to Sextus, the Pyrrhonian Way is “a disposition to oppose phenomena and noumena to one another in any way whatever, with the result that, owing to the equipollence among the things and statements thus opposed, we are brought first to epochē and then to ataraxia” (ph i 8). Here, “Epochē is a state of the intellect on account of which we neither deny nor affirm anything. Ataraxia is an untroubled and tranquil condition of the soul” (ph i 10).

Sextus tells us that the Pyrrhonian Way originated when “certain talented people” were upset by anomalies in “things” and tried to find out what is true, hoping thereby to achieve peace of mind (ataraxia), or more precisely, ataraxia regarding matters of doxa (opinion, belief; for discussion of the meaning of the word doxa see Moss and Schwab (2019), and below on adoxastōs) and moderate pathē in things that are unavoidable (ph i 12, 25). This is the telos for which everything is done or contemplated, the ultimate object of the desires (ph i 25). But when the future Pyrrhonists began to philosophize in order to assess their phantasiai as to their truth and falsehood, they were unable to resolve this as they landed in a controversy between positions of equal strength, leading them into epochē. As if by chance, the sought-after ataraxia as regards belief followed (ph i 25–27). Sextus compares this to a story about the famous painter Apelles: at one point Apelles got so frustrated with his attempts to paint the froth of a horse that he threw his sponge at the picture, and when striking the picture, the sponge produced the sought-after effect (ph i 28).

Not only does Sextus define the Pyrrhonian Way as above, but he also calls the practice of opposing to each statement an equal statement the basic principle of the Pyrrhonian Way. This practice, in turn, is taken by Pyrrhonists to bring dogmatizing to an end (ph i 12). Dogma, in this context, is used to denote assent to non-evident matters, as distinguished from something one merely agrees to, as the Pyrrhonist “does give assent to the pathē [feelings; or states of the soul (Mates 1996: 65)] that are forced upon him by a phantasia [impression, appearance, presentation (Mates 1996: 33)]; for example, when feeling hot (or cold) he would not say ‘I seem not to be hot (or cold)’” (ph i 13).

Epochē regarding non-evident matters extends also to the Pyrrhonist’s own statements. Sextus emphasizes already near the beginning of ph that

as regards none of the things that we are about to say do we firmly maintain that matters are absolutely as stated, but in each instance we are simply reporting, like a chronicler, what now appears to us to be the case.

ph i 4

Not even in putting forward the [Pyrrhonist] slogans about non-evident things does he dogmatize […]. For the dogmatizer propounds as certainty the things about which he is said to be dogmatizing, but the [Pyrrhonist] does not put forward these slogans as holding absolutely.

ph i 14

The Pyrrhonist does not only refrain from dogmatizing herself, but out of philanthropy wishes to cure by argument, so far as she can, the conceit and rashness of the Dogmatists (ph iii 280), who are distressed by their affliction of (self-)conceit (ph iii 281). Conversely, the Pyrrhonist needs to avoid being “tricked somehow by the Dogmatist into ceasing to raise questions about the arguments and through precipitancy should miss out on the ataraxia…” (ph i 205).

The Pyrrhonist does not have a system in the sense of attachment to a number of dogmata (ph i 16). Nevertheless, she does have “a way of life [which] follows a certain rationale […] that, in accord with appearances, points us toward a life in conformity with the customs of our country and its laws and institutions, and with our own particular pathē,” and also produces the disposition to suspend judgment (ph i 17). The Pyrrhonist therefore lives adoxastōs but in accord with the ordinary regimen of life, whose parts have to do with (a) the guidance of nature (“that by which we are naturally capable of sensation and thought”), (b) the compulsion of the pathē (e.g., hunger, thirst), (c) the handing down of laws and customs (“that by which we accept that piety in the conduct of life is good and impiety bad”), and (d) the instruction in arts and crafts (ph i 23–24).

Consistent with this, Sextus only claims that the Pyrrhonist achieves ataraxia with regard to doxai while still possibly being troubled by unavoidable pathē like feeling cold or thirsty. Nevertheless, even in the latter cases the Pyrrhonist is better off than ordinary people, because the latter are in addition affected by believing that these conditions are evil by nature (ph i 30).3

3 Criticisms

A considerable number of objections have been raised against the Pyrrhonian Way as presented by Sextus, starting already in antiquity. For example, for Galen “Mostly they [the Pyrrhonists] simply serve as suitable targets for insult” (Hankinson 2018: 169), and “on numerous occasions he [Galen] refers to agroikoi Purrhôneioi, peasant4 Pyrrhonists” (Hankinson 2018: 170). Galen complains, e.g., that according to the Pyrrhonists, “Swans should not be said to be white without first being subjected to logical investigation … At this point, we may realize we are faced with a Pyrrhonian aporia; or rather with a complete load of bollocks” (Galen, quoted from Hankinson 2018: 169).5

Even the great David Hume (1777: E 12.23) claimed that the Pyrrhonist “must acknowledge, if he will acknowledge anything, that all human life must perish, were his principles universally and steadily to prevail.” Other accusations levelled over the centuries include: self-contradiction is supposedly inherent in saying that one lives adoxastōs; epochē is allegedly psychologically impossible and/or rationally inadmissible; epochē supposedly makes life subhuman (like that of a non-human animal or even a plant); ataraxia cannot follow upon epochē or it is an undesirable state if it does; once in the state of ataraxia, the Pyrrhonist will not continue investigating, pace Sextus’ statement that he does; or such a life is not a philosophical one in contrast to what Sextus implies (see also the list in Vogt 2010: 166).6

Hume’s charge is a version of one of the strongest and most frequently repeated arguments against the Pyrrhonian Way, namely, the apraxia objection, which holds that universal epochē is incompatible with action,7 or at least with responsible and/or reasonable action. This apraxia charge is the topic of the present article. In this, I will follow the Pyrrhonian Way in that I will look at what a relevant present-day technē (cf. above ph i 24) tells us about how to deal with psychological disturbances, and what one can conclude regarding the apraxia charge. The technē of how to deal with psychological disturbances is of course psychotherapy, and so the next subsection briefly recalls what is known about the relationship of ancient (and in particular Hellenistic) philosophies and modern psychotherapies.

4 Ancient Philosophy and Modern Psychotherapy

Modern psychotherapy encompasses a considerable number of different approaches, usually grouped into psychodynamic (mainly going back to Sigmund Freud, and emphasizing subconscious dynamics often rooted in childhood), humanistic (going back to psychologists like Carl Rogers and former psychoanalysts like Viktor Frankl or Fritz Perls, emphasizing the human capacity for growth and desire for meaning), and cognitive-behavioral approaches. The latter are usually referred to as cbt (Cognitive-Behavioral Therapies) because they encompass behavioral methods rooted in the operant learning mechanisms studied in Skinner’s behaviorism (from the 1950s, now often called the first wave of cbt), to which cognitive techniques were added slightly later (the best-known contributors being Albert Ellis and Aaron Beck). Starting in the 1980s, a gamut of mindfulness-, acceptance-, and emotion-focused approaches evolved (including dbt [Dialectical Behavioural Therapy], mbct [Mindfulness-Based Cognitive Therapy], act [Acceptance and Commitment Therapy], and many others; most of which going back to Jon Kabat-Zinn’s mbsr [Mindfulness-Based Stress Reduction] program), which are collectively known as the third wave of cbt.

The cognitive side of cbt in particular is well known to have important roots in ancient Stoic philosophy (Robertson 2010), but Albert Ellis, for example, acknowledged being inspired also by Epicurean, Buddhist, and Daoist philosophies. Among humanistic approaches, existential psychotherapies connect to ancient philosophy in that they place central importance on Edmund Husserl’s phenomenology, which in turn is based on “Husserl reviv[ing] the Hellenist skeptic’s principle of epoché (epokhē)—also called phenomenological reduction or, simply, bracketing—which means the suspension of belief or judgement” (Cooper, Craig & van Deurzen 2019: 8). In their survey article on Existential Analysis, Längle and Klaassen (2019: 352) expand on this as follows:

Although the phenomenological procedure also assists in opening up and widening the person’s view of their world, phenomenology has a slightly different focus to Socratic dialogue.8 Phenomenology goes a step further. It not only loosens up taken-for-granted views and convictions but radically sets them aside (not even noticing them and working on them as is done in Socratic dialogue). This is called the “epoché” (Husserl, 1984), the bracketing of all knowledge, assumptions, judgments, and so forth. Phenomenology aims […] to live authentically and realize fully our being-in-the-world (Heidegger).

Nevertheless, Husserl may have understood epochē somewhat differently from the Pyrrhonists:

With a rather different purpose in mind (i.e., not seeking the equanimity of the ancient Skeptics), Husserl recommends his phenomenological epoché in order to suspend the thesis of the natural standpoint that permeates everyday life and even the sciences that are built on this naïve realist outlook.

moran 2021: 105

Indeed, Öymen attempted an existentialist reconstruction of Pyrrhonism, but concluded both that “[e]xistentialism needs to replace Edmund Husserl’s phenomenology with Pyrrhonian phenomenalism and it needs to supplement its ontology with a sceptical epistemology” (2012: 12), but also questioned the goal of ataraxia and asked rhetorically: “How can ambiguity and uncertainty be a source of tranquility? Why should it be? Why tranquility? Why not anxiety?” (2012: 11). He concluded that Pyrrhonism needs to give up on ataraxia and instead should embrace tarachē, the anxiety that according to Öymen results from epochē.

It follows from the study below that Öymen is likely wrong in thinking that Pyrrhonists have to give up on ataraxia. Nevertheless, this is a side result; my main interest is not in the relationship of the Pyrrhonian Way with existential psychotherapies, but in that with third-wave cbt s, and in particular with one particular form thereof: act. There are a number of reasons for this. Most importantly, among the various forms of psychotherapy, cbt is by far the best studied both in terms of clinical efficacy and of basic mechanisms. Also, an indirect connection between the Pyrrhonian Way and modern psychotherapy may be discerned, if, as is sometimes assumed, the Pyrrhonian Way is a Greek version of Buddhism (e.g., Kuzminski 2008, 2021 and Beckwith 2015, but contrast Batchelor 2016), because Buddhism, in turn, provided a crucial basis for the third wave of cbt (Hayes 2002, Kabat-Zinn 2011). In fact, “mindfulness” is simply the standard English translation of the Buddhist technical term sati.9 Furthermore, Brons (2018) argued for the livability of Pyrrhonism on the basis of similarities with the Madhyamaka school of Buddhism, specifically with the Gelug school of Tibetan Buddhism. At first sight, this may appear surprising, given the emphasis that many interpretations of Buddhism put on sammā-diṭṭhi (often translated as “right view”), but (at least in Theravada Buddhism) this need not be understood as adherence to a fixed dogma (Fuller 2005).

Among the various forms of third wave cbt, act stands out in not being based on Kabat-Zinn’s mbsr program, and in claiming to have bypassed the cognitive wave in cbt, thus having proceeded directly from behaviorism to the acceptance- and mindfulness-based third wave. This is relevant in the present context for the following reason: Versteegh (2020) argued that there are important similarities in the attitude towards language between Skinner and Sextus, to the extent that “Skinner’s Radical Behaviorist project could […] take its place as a modern-day heir to the [Pyrrhonian] way of life” (2020: 2). This in itself would seem to be of little help for present purposes, as Skinner’s theory of verbal behavior is widely seen as hopelessly flawed. Indeed, one of the crucial ingredients in the development of act was the development of a novel behavorist theory of language—Relational Frame Theory (rft), on which see Hayes, Barnes-Holmes and Roche (2001)—as a reply to the criticisms advanced against Skinner’s theory of verbal behavior (Skinner 1957), most prominently by Noam Chomsky (1959). Furthermore, a distinctly behaviorist aspect of the Pyrrhonist Way can also be recognized in the observation that “the [Pyrrhonist] yields appropriately to stimuli” (Thorsrud 2003). Conversely, act has been argued to parallel Stoic philosophy (Gill 2019). The present paper contends that the parallels with the Pyrrhonian Way are even greater, and that these parallels illuminate both the practicality of living the Pyrrhonian Way as well as the philosophical basis of act.

5 ACTing in an act Manner

act has a remarkable evidence base: at the time of writing, over 400 randomized controlled trials and a considerable number of meta-analyses demonstrated its efficacy and effectiveness in treating a wide variety of psychological problems, generally at least on a par with other state-of-the-art psychotherapies (Hayes, Strosahl & Wilson 2012, Hayes 2019, Gloster et al. 2020). The central claim in act is that “psychological rigidity is a root cause of human suffering and maladaptive functioning” (Hayes et al. 2012: 64) and, conversely, psychological flexibility is the hallmark of mental health (Kashdan & Rottenberg 2010). The following is worth quoting at length:

The psychological flexibility model holds that pain is a natural consequence of living but that people suffer unnecessarily when their overall level of psychological rigidity prevents them from adapting to internal or external contexts […]. Unnecessary suffering occurs when verbal/cognitive processes tend to narrow human repertoires in key areas through cognitive entanglements and experiential avoidance. When people overidentify, or “fuse,” with unworkable rules, their behavioral repertoire becomes narrow, and they lose effective contact with the direct results of action. […] Being “right” about what is wrong can become more important than living a vital and effectual life.

hayes et al. 2012: 64
Superficially, this may seem similar to standard assumptions in cognitive therapy, i.e., dysfunctional cognitions and the apparent need to change them:

In a nutshell, the cognitive model proposes that dysfunctional thinking […] is common to all psychological disturbances. When people learn to evaluate their thinking in a more realistic and adaptive way, they experience a decrease in negative emotion and maladaptive behavior.

beck 2020: 4
Nevertheless, there is a crucial difference. From the act viewpoint,

It is not so much that people are thinking the wrong thing; rather, the problem is thought itself and how the wider community supports the excessive literal use of words and symbols as a mode of behavioral regulation.

hayes et al. 2012: 65

Largely based on basic research in psychology laboratories, the psychological flexibility model encompasses six interrelated and interdependent core processes—usually depicted in a hexagon-shaped design that is colloquially referred to as the hexaflex, in order to emphasize this interdependence. These processes contribute to psychological inflexibility, with six corresponding core processes constituting psychological flexibility (Hayes et al. 2012: 62–63):

  1. Inflexible attention / flexible attention to the present moment.
  2. Experiential avoidance / acceptance of current experience for what it is (not necessarily approving it).
  3. Cognitive fusion / defusion.
  4. Attachment to the conceptualized self (“self-as-content”) / observer-self (“self-as-context”)
  5. Lack of awareness of one’s deeply held values / values.10
  6. Inaction, impulsivity, or avoidant persistence / committed action in line with one’s values.11

Empirical research found strong support for this model. Already in 2010, a review study reported that

act components have been tested in more than 40 studies […] Significant effect sizes were found for defusion, values, contact with the present moment, mindfulness components (combinations of acceptance, present moment, defusion, or self as context), and values plus mindfulness in comparison with techniques such as thought suppression or distraction. […] Across all studies, about 50% of the between-group differences in follow-up outcomes can be accounted for by the mediating role of differential post levels in psychological flexibility and its components.

hayes et al. 2010: 156–157

Importantly, none of the six processes seems to be redundant, as in a recent study each psychological flexibility process was found to separately mediate improvements in mental health (Levin, Krafft & Twohig 2020). This therefore applies in particular to the defusion process. Further evidence for the beneficial nature of cognitive defusion comes from recent research in posttraumatic stress disorder, which concluded that “the deleterious relationship between maladaptive posttraumatic cognitions and pts symptoms was stronger for those who were more highly fused to their cognitions” (Benfer, Rogers & Bardeen 2020: 55), and from the effect sizes for the core processes reported in Levin, Hildebrandt, Lillis and Hayes (2012: 749, Table 2).

Thus, act research demonstrates two facts that will be crucial in what follows: (a) defusion is possible, and it is not only compatible with, but actually an important ingredient in, living a valued life and acting according to one’s values; and (b) the same applies to self-as-context. It will be argued that the Pyrrhonian Way is importantly similar to act, and in particular that cognitive defusion is a reasonable interpretation of the Pyrrhonist’s state of being adoxastōs. If so, then the two facts just mentioned suggest that living the Pyrrhonian Way may not only be possible, but actually contribute to a full and vital life—pace the apraxia objection. Nor is the Pyrrhonian Way to be feared because it supposedly leads to a strange or non-existent self: it only encourages to let go of particular self-concepts when this is necessary, which is an ability that contributes to psychological flexibility rather than being a threat to be afraid of.

6 Sextus and the Hexaflex

Peace of mind may have been widely seen as a telos both in ancient Greece and India (McEvilley 2002: chap. 25) so that ataraxia may not have been a defining feature of the Pyrrhonian Way in setting it apart from other Greek philosophies.12 Nevertheless, Sextus is unambiguous that the telos of the Pyrrhonist is not to be unnecessarily disturbed. In act language, ataraxia is the Pyrrhonist’s value;13 but a Pyrrhonist would not claim that ataraxia is of objective value, nor would she be dogmatic about ataraxia being the telos or forecast that it will always be of value to her,14 just as in act “[e]ven values should be held lightly rather than fused with” (Harris 2009: 29). In fact, according to Sextus, the difference between the Pyrrhonist and the dogmatist is precisely that the “dogmatizer propounds as certainty” (ph i 14) her claims, while the Pyrrhonist does not “firmly maintain that matters are absolutely as stated” (ph i 4). Consistent with this, Eichorn (2014: 133) suggests that Sextus’ use of the expression adoxastōs (usually translated as without belief or without opinion) should be understood as without dogma in the sense of undogmatic.15 Unlike the dogmatist, who is fused with his mental contents (thoughts, and beliefs in particular) and therefore prone to inflexible rule-governed behavior (Hayes et al. 2012: 52–56), the Pyrrhonist does not mistake her beliefs for reality and therefore can act in line with her values16 in whatever way is appropriate in the given context.17

“[T]he human being is by nature a truth-loving animal” (ad i 27 = am vii 27, in Bett 2005). Maybe for this reason, the future Pyrrhonists were disquieted by the anomalies in “things” (pragmata) and turned to philosophizing in the hope of finding the truth and thereby attaining ataraxia (ph i 12). Now, generally, any inquiry into truth can lead to a conclusion (either a belief that is taken to be the truth, or that the truth is that the truth cannot be found), to continuing inquiry, or to the abandonment of inquiry. Hence, at ph i 2–4, Sextus distinguishes three kinds of philosophies: Dogmatic, Negative Dogmatic,18 and Pyrrhonian (presumably, abandonment does not count as a philosophy). Characteristic of the (future) Pyrrhonian philosopher is that, in her pursuit of the truth, she found herself confronted with positions of equal strength (ph i 26), a fact that she did not sweep under the rug (am i 6). This led her into a state of intellect in which she neither affirmed nor denied anything (i.e., epochē, ph i 10). As if by chance, the sought-for ataraxia followed “as a shadow follows the body,” because the Pyrrhonist feels no need to avoid or to pursue anything intensely given that she does not believe that anything is good or bad by nature (ph i 28).

Thus, the way the Pyrrhonist attained ataraxia was not the way which she had expected would lead to it (i.e., by disputing erroneous assumptions and correcting them, cognitive therapy style), but by letting go of the inner compulsion that she must achieve ataraxia, and of the (implicit) dogma that this has to be done by finding the truth. Sextus compared it to what had happened to Apelles when he despaired of his attempts to paint “correctly” and let go of the compulsion to do so, in fact he even did something (throwing the sponge at the picture) he might have expected to harm his efforts; but suddenly the desired effect happened. Similarly, the Pyrrhonist despaired of adjudicating between different beliefs, let go of the compulsion to find the true belief (i.e., she was in epochē), and suddenly the desired effect happened (without time delay: the shadow follows the body synchronously!). What the Pyrrhonist understood at this point is that “the ultimate reason why unresolved conflicts were a source of disturbance [was] the belief that discovering the truth is of objective value” (Machuca 2020: 439 n. 7)—at least the belief that having the truth is of objective value in being necessary for living in line with one’s values (and thus without inner conflict, i.e., in ataraxia)—a belief that had persisted despite the repeated experience that the anxiety-driven search for the truth did not lead to ataraxia. In act jargon, both Apelles and the Pyrrhonist seem to have profited from being in a state of Creative Hopelessness:

[I]f the client can give up on what hasn’t been working, maybe there is something else to do. Thus, we are trying to help clients trust their own experience and begin to open up to a transformational alternative. […] [T]he objective is to give up strategies when the client’s own experience says they do not work, even when what comes next is not yet known.

hayes et al. 2012: 189–190, italics in the original.

This leads us back to the concept of psychological flexibility. On the interpretation advanced here, the Pyrrhonist was lucky enough to enjoy the salutary experience of letting go of rigid rules (such as: Thou must find the truth to be at peace), thus learning to be able to defuse from unhelpful mental content. Far from paralyzing the Pyrrhonist, the state of being defused (adoxastōs) actually enables valued action, as both theory and empirical research in act show.

Under this interpretation, we can also suggest an answer to the question of what kind of self a Pyrrhonist can have (Bett 2019), and whether such a self is somehow deficient in, for example, being overly detached from itself. The suggested answer is that the Pyrrhonist has a healthy and flexible self, namely, self-as-context: the self that is in the present moment and experiences life to its fullest, while avoiding the perils of self-as-content—a rigid self-image that suffers more than necessary when it needs to adjust to changing circumstances. For example, the person fused with her self-image as mother not being able to adjust to the children moving out, or the person with the content “I am a mountaineer” despairing when the knees stop working properly, or the cognition-maketh-the-human philosopher who notices signs of possible dementia showing up in her, etc.—all these are likely to suffer from their rigidity in addition to the natural psychological reactions, such as sadness in the case of experiencing a loss (cf. ph i 30). Far from the apraxia that armchair philosophers dream up, there are reasons to expect the Pyrrhonist to live a life which is more vibrant and fuller than that of the dogmatist.

7 Discussion, Part 1: a Good Life?

Many authors have asked whether the Pyrrhonist can “act normally” or “lead a normal life.” What is a normal life? There is overwhelming evidence that despite improving physical health, mental health and wellbeing are not improving. Rather,

Mental illness is rapidly becoming much more of a problem, not less. In 1990, depression was the fourth leading cause of disability and disease worldwide after respiratory infections, diarrheal illnesses, and prenatal conditions. In 2000, it was the third leading cause. By 2010, it ranked second. In 2017 the World Health Organization (who) ranked it number one.

hayes 2019: 4

According to the who, more than 350 million people were affected by depression in 2014 (Ledford 2014, Smith 2014). Add to this the large number of people suffering from other forms of mental distress, from schizophrenia through panic attacks to personality disorders and other mental diseases, not to mention subclinical disturbances like permanently elevated stress levels. If this is normal life for a large part of the population, why would the Pyrrhonist be interested in living such a “normal” life?19

If act is right in positing that much of this mental distress stems from cognitive entanglements, experiential avoidance, and fusing with unworkable verbal rules, then defusion is an important skill contributing to a healthy and happy life. Thus, Striker (2004: 20) is absolutely right to note that the Pyrrhonist is able to take

the attitude of a neutral observer even to his own inclinations. […] [H]e will be disturbed by pain, since he is a sentient creature, but he will not aggravate matters by adding the judgment that pain is really bad, or piety really good. By distancing himself from his own reactions and beliefs, he preserves his peace of mind […].

But she is wrong in seeing this as a problem. On the contrary, it is a rare and valuable ability of the Pyrrhonist to “constater, comme un simple spectateur, les pensées qu’il trouve chez lui en tant que doué de raison” (Machuca 2019: 82), instead of overidentifying with thoughts and beliefs and thereby possibly losing contact with the events actually happening at the moment:

act is designed to: a) lessen the degree to which thoughts are taken literally and to promote the evaluation of thoughts on the basis of the degree to which they lead to valued life changes, b) undermine reason-giving and believability of reasons in areas where these efforts have been used to justify and excuse ineffective behavior, c) foster the experience of private events, rather than engage in counterproductive avoidance behavior, d) clarify life values and identify barriers to implementation of life goals, and e) foster commitments to actions linked to life values.

hayes et al. 2001: 235
To emphasize that these considerations are based on rigorous research rather than mere armchair speculation, here are a few more relevant quotations from the scientific literature:

When a person responds almost exclusively to the verbal conditioned functions of a stimulus to the detriment of other, nonverbal stimulus control, act therapists use the middle-level term cognitive fusion […]. [T]he individual may be insensitive to the current environment and remain under the control of derived verbal relations […] Furthermore, even if the person comes into direct contact with the altered contingencies, it may not be sufficient to alter his or her responding […]. After all, the maintenance of verbal coherence is a powerful automatic reinforcer […] and it may be stronger than the reinforcement instated by the new contingencies.

assaz et al. 2018: 407–408
Hayes and his colleagues also noted that

mindfulness-based therapies, act, and other methods are known to produce an unexpected desynchrony between thought or emotion and behavior. In other words, as a result of these methods, the same emotional or cognitive content now functions in a different way.

hayes et al. 2001: 158
In a way, this means living a less “normal” life, and this is precisely the intention: living a more serene (or at least less disturbed) rather than a normal life. In computer jargon, “this is a feature, not a bug”—whether for the Pyrrhonist or in third wave cbt. As can already be seen in the last quote above, act is not alone in seeing benefit in loosening overly tight connections between cognition and action. That evaluative judgements are problematic can, for example, be seen in the meta-analyses of correlates of mindfulness facets which were performed by Carpenter et al. (2019) and Mattes (2019b). Consistent with this, in their survey article on the neuroscientific basis of mindfulness-based programs (mbp s) in psychiatry, Schuman-Olivier and his colleagues noted that

evaluative judgment is deemphasized during mbp s in favor of developing a focus on acceptance, intention setting, and attention toward experiential monitoring rather than self-evaluation.

schuman-olivier et al. 2020: 376

Mindful self-regulation starts with attentional control and curiosity about present-moment experience, leading to the development of interoceptive awareness and alternatives to self-critical rumination. Reappraisal of mental content, decentering, and acceptance downregulates autonomic reactivity, allowing for exposure to aversive internal stimuli and ultimately developing equanimity.

[…] As one begins to pay attention, consistent curiosity and kind awareness allow greater goal-driven control based on values, increased levels of internalized motivation, greater access to intrinsic motivation, and less reliance on stimulus-driven conditioning and evaluative negative feedback systems, eventually unwinding associative learning related to harmful behaviors.

schuman-olivier et al. 2020: 378

Such an approach may be to the horror of some philosophers, but it is to the benefit of human beings, be they the psychiatric patients or those “only” suffering from “normal” mental distress.

8 Discussion, Part 2: Life without Belief?

What does all this imply for the question of how and why Pyrrhonists live “without belief”? This question can be understood in two ways: from Sextus’ point of view or from a contemporary viewpoint (cf. Fine 2000: 81). From Sextus’ perspective, the question is ill-posed: he never claimed to live without belief, for the simple reason that he did not write in English, if nothing else. Instead, Sextus talked about being adoxastōs. The present paper hinges on reading adoxastōs as “undogmatically,” rather than the literal reading “without doxa,” in this following Eichorn and others (see Section 5 above). Its original contribution to the literature consists in pointing out that this reading can be fruitfully understood in terms of the technical term “defusion,” as well as sketching how the scientific evidence implies that under this reading one can make sense of the Pyrrhonian Way of living and acting,20 and that even the idea of this leading to (or at least progressing in the direction of) ataraxia is made plausible. Whether the reading of adoxastōs as “undogmatic” is indeed a live possibility from a philological standpoint is a question I do not feel able to opine on, but if it is (as the discussion by Eichorn suggests), then the above considerations show that modern psychology lends support to it, and conversely.21 This results in a virtuous circle, with the psychological understanding lending credibility to the philosophical reading, which in turn lends additional credibility to the psychological understanding.

Second, whether Sextus claims to live without beliefs in the contemporary English sense of the word depends of course on the precise meaning of “belief.” Since a full discussion is not possible in this article, I will restrict myself to a brief remark on what Fine (2000: 83) calls the standard view of belief, namely that believing p means taking p to be true. The suggestion put forward in the present paper is that Sextus is not so much concerned with taking something to be true, but with the ability to let go of truth claims. For example, suppose someone well-off is fused with (i.e., inflexibly holds) the thought (belief? opinion? doxa? dogma?) that only the rich can be happy,22 and accordingly spends her entire time and energy on running her company. Then for some reason she goes bankrupt and falls into depression with the resultant inactivity, because of her being fused with the thought that she cannot be happy without riches.23 If, alternatively, under the same circumstances she holds this thought lightly and flexibly, not mistaking it for an absolute truth (cf. ph i 14, as discussed above), this likely would have prevented her from falling into depression and enabled her to reorient herself towards other sources of meaning, happiness, and fulfilment (e.g., family, charity work, spirituality, art, meditation, among many other possibilities). Would that thought still have counted as a belief under the standard view, i.e., did she take “only the rich can be happy” to be true, in the alternative case in which she held it flexibly? Evidently, she would not have taken it to be the immutable truth, the whole truth and nothing but the truth. Whether despite this it does amount to holding it true simpliciter, so that it qualifies as a belief in the sense of Fine (2000), seems to me a highly non-evident and in practice entirely irrelevant matter that I prefer to suspend judgement on.

9 Discussion, Part 3: Apraxia?

If one understands adoxastōs literally (and uses “belief” in a wide sense encompassing implicit beliefs, as for example Fine 2000: 86–87), then it may be natural to wonder how a Pyrrhonist can act. On the other hand, if the present suggestion to understand adoxastōs as “defused” makes sense, then it is unclear what the apraxia objection would rest on: given that the crucial difference between the Pyrrhonist and the dogmatist is that the Pyrrhonist recognizes that her beliefs (if this is the right English word) are not absolutely true, it is more likely the dogmatist who is obstructed in acting freely and appropriately to circumstances. In terms of the example above: a belief like “Only the rich can be happy,” if held as an absolute truth, tends to prevent possible valued action as well as adaptation to changing circumstances. The Pyrrhonist might challenge this rigid belief (e.g., does everyone agree with this thought? did it hold in Pnom Penh 1975, Beijing 1948, or Saint Petersburg 1917?), but importantly, she does understand that she need not replace it with another “truer” dogmatic claim (cf. Section 6 above). After all, one does not need to treat one’s thoughts as certainties that hold absolutely (cf. ph i 14) in order to act on them; it is sufficient to be aware of what appears to be the case (cf. ph i 4); hence, the Pyrrhonist does not suffer from apraxia.

10 Conclusions

In this essay, I proposed to look at the Pyrrhonian Way from a psychological point of view. The rough guiding idea is that its basic insights relate to third-wave cbt in a way similar to that in which Stoic philosophy relates to second-wave cbt; and in particular that Eichorn (2014: 145) is right in saying that in the view of Pyrrhonists, “beliefs in themselves are not the problem; rather, what is troubling and dangerous is people’s attitude toward their beliefs.” In act jargon, this problematic attitude is called “cognitive fusion,” with its opposite being “defusion.” I argued that the crucial term adoxastōs can be understood as defused in this sense; and that, if so understood, the science underpinning act shows that the Pyrrhonist can live an at-least-as-good-as-normal life—quite the opposite of the halting of all action and perishing of life, which David Hume imagined and many others still seem to fear.

Admittedly, my proposal de-emphasizes the practice of opposing to every proposition an equal proposition, even though it is referred to as the basic principle of the Pyrrhonian Way (ph i 12). Here is a possible justification for this: from an act point of view, one uses whatever tools work to increase psychological flexibility, be that the psychotherapeutic use of metaphors, meditation (as in Buddhism), opposing propositions to each other (as in Sextus), or whatever else helps the patient improve. Conceivably, opposing propositions may have worked best in the intellectual climate of ancient Greece, and it might have been useful to emphasize it in discussions with other philosophical or medical schools of the time—this might explain why Sextus exclusively focuses on this technique.24

Even if this makes sense, the present article still leaves a lot of open tasks: discussing in detail the various forms of the apraxia objection (Vogt 2010: 166, Machuca 2019: 63); exploring the question as to how deep a peace of mind an act-like approach can lead to under optimal circumstances (compared for example to the upekkha in deep Buddhist meditation); asking whether Sextus would have claimed to be able to cure all mental disturbances;25 reconciling the work of Attie-Picker (2020) with the evidence base of act; and much more.

However that may be, one main aim of the present article is to suggest that those philosophers who (for example) “wonder whether the state of mind ascribed to the Pyrrhonist is psychologically possible or perhaps rather pathological” (Striker 2004: 22)26 might actually get out of their armchair and ask knowledgeable people (psychologists, psychotherapists, psychiatrists) about what is psychologically possible and about what is pathological.27 A philosophy that makes claims about scientific (including psychological) matters without at least trying to take potentially relevant science into account is a dead end (Hawking & Mlodinow 2010).


I am grateful to Diego Machuca and an anonymous reviewer for helpful comments on earlier versions of this manuscript. All remaining errors are of course mine.


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It is disputed to what extent the works of Sextus agree with the teachings of Pyrrho: see Machuca (2011: 246–247) and Kuzminski (2008: 38–41). I will follow Sextus in referring to his way as Pyrrhonian.


ph: Pyrrōneioi Hypotypōseis (Outlines of Pyrrhonism) consisting of three books. I use the translation by Mates (1996) unless otherwise indicated. ad: Adversus Dogmaticos (Against the Dogmatists), consisting of five books (also known as am VII–XI). am: Adversus Mathematicos (Against the Professors), consisting of six books.


See also ph iii 235: The Pyrrhonist, “seeing so much anomaly [disagreement] in the matters at hand, suspends judgment as to whether by nature something is good or bad or, generally, ought or ought not be done, and he thereby avoids the Dogmatists’ precipitancy, and he follows, without any belief [adoxastōs, Bury (1933) translates it as “undogmatically”], the ordinary course of life; for this reason he has no pathos one way or the other as regards matters of belief, while his pathē in regard to things forced upon him are moderate. As a human being he has sensory pathē, but since he does not add to these the belief that what be experiences is by nature bad, his pathē are moderate.”


Terminology revived by Barnes as “rustic” (1982: 2): “The rustic Pyrrhonist has no beliefs whatsoever: he directs epoche towards every issue that may arise. The second type of Scepticism I shall call urbane Pyrrhonism.”


Galen’s claim constitutes an interesting case of dogmatic rashness, as there are black swans (see Taleb 2007). Given Galen’s towering influence in the history of medicine (Wootton 2007: 5), one may wonder how much damage his dogmatic rashness did via his enthusiasm for bloodletting, a therapy that in the vast majority of cases is useless at best, and fatal at worst (Ernst & Singh 2008: 20–23).


Recent examples include Striker (2004: 20, 2010: 205), Burnyeat (2012: 235), and Barnes (2014: 408–409).


“L’un des arguments les plus forts et les plus fréquemment répétés contre le scepticisme antique, dans ses deux variantes académicienne et pyrrhonienne, est l’objection de l’inaction (ἀπραξία)” (Machuca 2019: 53).


A standard technique in cognitive therapy.


See Mattes (2019a) for a discussion of the extent to which this fact is or is not important to secular psychotherapy.


It may be worth emphasizing that values, as understood in act, do not express beliefs, at least not if “belief” is understood as “taking something to be true” (see Fine 2000: 88). Values, as seen in act, are certain behavioral patterns that establish reinforcers for specific behaviors (Wilson 2009: 66). In this way, they “function as ‘final causes’ of behavior” (Hayes et al. 2012: 94).


This ordering is conventional, but implies nothing about any of the processes having a special role. Italicized are the standard names for the flexibility processes.


Compare Machuca (2020: 449): “In the final segment of the Pyrrhonian Outlines (ph i 209–241) devoted to exploring the differences between Pyrrhonism and its neighboring or nearby philosophies, Sextus’s main reason for refusing to consider a given philosophy as skeptical is that its advocates do not suspend judgment or do so only partially. Only twice in that segment does he mention undisturbedness.”


On some readings, reaching ataraxia may be compared to reaching nirvana, which is explicitly mentioned as a possible act value by Wilson (2009: 66).


Compare Machuca (2020: 439): at ph i 25, “Sextus is […] recognizing that undisturbedness might cease to appear to the skeptic as a state of mind worth experiencing.”


See his lengthy footnote 17 for details, as well as Eichorn (2020: 205), who compares dogmata to what Nietzsche’s calls Überzeugungen (convictions) as opposed to Meinungen (opinions), with Überzeugung being “the belief that we possess the absolute truth about some specific point of knowledge,” whereas the Pyrrhonist has a “modest, undogmatic, ‘unopinionated’ attitude toward one’s own first-order beliefs (what Sextus refers to as living adoxastôs).”


Nor do act practitioners mistake their values for objectively true beliefs. In fact, technically, in act “values” (more strictly speaking: valuing behavior(s)—remember this is a branch of behaviorism, mentalistic entities are at best a figure of speech) are certain behavioral patterns that establish reinforcers for specific behaviors. To take a standard example, “valuing being a good parent” establishes reinforcers for spending time with your children (e.g., it feels good), paying attention to them, etc. This is different from believing you should be a good parent, that it is of objective value to be a good parent—that can be just rule-following behavior, can be self-incongruent (e.g., you may feel forced to do it), etc.; of course, a belief that one should be a good parent is consistent with valuing being one, but it is not constitutive of it. Or consider valuing being a prolific academic: that may not reinforce spending time with your children, instead it may reinforce spending time at the library, and other behaviors. Or take valuing collecting stamps: I suppose no one would hold this to be of objective value, but it can reinforce behavior—and match the other characteristics of valuing—and indeed give meaning to a person’s life.


Eichorn (2014: 127) referred to Sextus as a “proto-contextualist,” but distinguished only between philosophical and non-philosophical contexts. act is avowedly contextualist in a way that goes far beyond distinguishing only between these two contexts.


Using modern terminology. Sextus referred to it as “Academic” since he ascribed it to the new Academy of Clitomachus and Carneades (ph i 3, 220, 226–231); but it is disputed whether he correctly represented their views.


It may also be worth remembering that the likes of Socrates, or the Buddha, or Jesus, did not lead normal lives, either.


How acting in line with one’s values (as understood in act) relates to other philosophical notions of “acting” is beyond the present discussion. I suspect an adequate discussion would require a book-length treatment.


For the latter claim, see Mattes (2021).


At am ii 53, Sextus uses “the rich man is ‘blessed’” (translation by Bury 1949) as an example for something non-evident that is a matter of opinion.


This is an example of how rigidly held beliefs can lead to distress. A full discussion about how fusion and psychological inflexibility lead to disturbance is beyond the scope of the present paper. The interested reader is referred to the literatures on act, and on clinical psychology in general.


Speculative note: there may be hints of other techniques employed by Pyrrhonists: Sextus indicates a preference for non-activity (ph i 23), which might conceivably relate to meditation. Diogenes Laertius writes about Pyrrho walking supposedly carelessly around, but this could very well be Pyrrho engaging in walking meditation which was later caricatured by his dogmatic opponents. Also, Pyrrho’s frequent withdrawing into solitude would fit into this.


From today’s point of view, psychotherapy (of whatever form) alone is insufficient as a treatment for disturbances such as bipolar disorder or schizophrenia.


Striker (2004: 20) also wonders whether “the attitude of a neutral observer even to his own inclinations […] could be maintained by any ordinary person, or indeed whether it helps to think that pain is bad, but perhaps not really bad.” As explained above, the scientific answer to both questions is “yes.”


How much psychological flexibility would philosophers need for this? Is it in line with the philosophers’ values, whatever these may be?

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