‘Philosophy of Psychedelics’ Book Forum: Part Five

Chris Letheby offers reflections in the light of four reviews of his book, Philosophy of Psychedelics (Oxford University Press, 2021).

This is Part Four of a Book Forum on Philosophy of Psychedelics. The Forum consists of four reviews and a reflection from the author.

For Part One by Nathan Emmerich and Bryce Humphries, click here.

For Part Two by Evgenia Fotiou, click here.

For Part Three by Nicolas Langlitz, click here.

For Part Four by Sandeep Nayak, click here.

I would like to thank all of the reviewers for their generous and thought-provoking engagement with the ideas developed in Philosophy of Psychedelics (POP), and Dr Tehseen Noorani of The Polyphony for curating this review series. In this response I offer some brief reflections on some (but certainly not all!) of the excellent points raised in the four reviews.

One point raised by multiple reviewers (Emmerich, Humphries, and Fotiou) has to do with the scope of the arguments in POP. Emmerich and Humphries comment that I am not “averse to any one individual adopting a supernatural metaphysics as the result of their psychedelic experiences”, being only concerned that “naturalism can account for [i.e. explain] such experiences”. In a similar vein, Fotiou says that my arguments, being made from the perspective of Western philosophy, can only apply to psychedelic use in Western contexts.

On both counts, my intention was to say something more far-ranging and controversial. In POP I am, indeed, interested in what individuals ought to believe on the basis of their psychedelic experiences. Of course, the idea is not that anyone ought to police anyone’s beliefs, or that anyone ought to be prohibited from believing certain things. The question is rather: assuming, as I argue briefly in chapter 2 of POP, that truth and knowledge matter in their own right, what should we, as individuals, believe about our psychedelic experiences? When psychedelic experiences cause people to hold beliefs that are false, or unjustified, then those experiences – by definition – harm those people epistemically. Where there is room for controversy is in (i) just how much epistemic harms matter, and (ii) which beliefs are the false or unjustified ones.

Consider the case of Julian Haynes, discussed in chapter 10 of POP. Haynes spent his life savings building a floating pyramid on the Amazon to communicate with aliens encountered in an ayahuasca experience (Mann 2011). Clearly, Haynes was harmed financially by his adoption of certain beliefs on the basis of this experience. Equally clearly, in my view, he was harmed epistemically: his psychedelic experience caused him to adopt beliefs that were both false and unjustified. According to my philosophical stance, this, in itself, is a harm worth caring about, quite apart from any financial or other harms it may cause.

Of course, it is possible to contest this evaluative claim; it is equally possible to dispute my specific verdicts about which psychedelic-induced beliefs are true and false, justified and unjustified. But it is worth clarifying that a large part of my concern in POP is, indeed, how transformative psychedelic use might affect the epistemic welfare of users, as well as their physical, mental, emotional, spiritual, and (perhaps, in some cases) financial welfare. One recurring concern about psychedelic use has been that it makes people irrational, or causes them to lose touch with reality; this, I think, is a concern worth taking seriously and exploring.

I hold that the truth, plausibility, and justification of our beliefs about the world matters in its own right. If this is so, then the epistemic is one of several dimensions along which psychedelic use may benefit or harm us. Further questions then present themselves: what benefits and/or harms does this use typically have, along these various dimensions; how much do these benefits and/or harms matter; and how might we increase the benefits and reduce the harms? Answers to these questions can contribute to an overall evaluation of the transformative use of psychedelics. My conclusion in POP is that, even from a naturalistic perspective, the epistemic benefit/harm ratio comes out pretty well – but I think it is important that we ask the question.


Along related lines, Fotiou notes a significant point of agreement between me and some of her Peruvian shamanic informants: these shamans, too, hold that some psychedelic-induced cognitions are accurate, while others are not, and that it is important to be able to draw the line. Presumably the shamans and I disagree about where, and how, to draw this line. But whatever the correct answer is, if we are speaking of truth, then there can – in my view – only be one correct answer. These issues require delicacy and tact, and the loaded term “delusion”,  which I used in POP in a non-clinical sense, is ill-suited to the purpose. But there is no getting around the fact that, according to my philosophical stance, if people who use psychedelics in Western contexts are incorrect to believe in a cosmic consciousness or spirit world, then people who use psychedelics in indigenous contexts are also incorrect to believe in such things.

It may be problematic anthropologically – and perhaps diplomatically – to suggest that most indigenous psychedelic users hold false beliefs about their psychedelic use; however, it is equally problematic philosophically to suggest that the spirit world really exists for Peruvian shamans but not for Johns Hopkins trial volunteers. This amounts to an ontological relativism that many philosophers, myself included, find implausible. Of course, different (groups of) people have different beliefs about such matters, and these ought to be approached with respect and epistemic humility. But as for the spirit world and the cosmic consciousness themselves, either they exist or they do not. If we disagree about whether they do, then one of us must be wrong. (Of course, many Western psychedelic users and researchers hold non-naturalistic metaphysical beliefs about psychedelic experiences; the philosophical position that I articulate in POP ascribes false beliefs to these people as well as to most indigenous users. As such, the issue is epistemological and ontological, rather than primarily cultural.)

Interestingly, at least one dyed-in-the-wool analytic philosopher, Steven Hales (2006), takes a different line, defending relativism about philosophical propositions. This is interesting partly because Hales’ arguments involve comparing three belief-forming practices: analytic philosophy, Christian revelation, and shamanic psychedelic use. His arguments are sophisticated, but I am not yet persuaded. Some form of methodological relativism is doubtless the right approach in anthropology, but ontological relativism as a philosophical doctrine is another matter. Many psychedelic users from different cultural backgrounds and contexts of use converge on Huston Smith’s “central message”: that “there is another Reality that puts this one in the shade” (2000, p. 133). My most basic assumption in POP is that either there is such a Reality or there is not, irrespective of what anyone thinks about the matter. And I believe there is not. As always, of course, I may be wrong. Perhaps the shamans and psychonauts are right, and some psychedelic apprehensions of another Reality are veridical; perhaps Hales is right and the truth is relative to varying perspectives, absolutist pretensions notwithstanding. Either way, it is good to have an opportunity to clarify the nature of those pretensions on my part.


The cross-cultural issues raised by Fotiou’s analysis are echoed by Langlitz’s intriguing strategy of rendering the intellectual and cognitive medium of POP opaque. Langlitz notes, correctly, that a naturalist philosophical perspective on psychedelics is not the only one possible; indeed, among those who take psychedelic experiences seriously, I suspect it is a minority position. I also strongly suspect it is correct, and the urge to say something for it in an academic setting has driven a lot of my work on the philosophy of psychedelics to date.

Many philosophical problems arise when we confront two or three propositions that seem independently plausible but inconsistent with one another. The work is then in determining whether it is the apparent inconsistency, or the apparent plausibility of one or more proposition, that is illusory. One way of understanding POP is as a response to the apparent inconsistency between two propositions, each of which seems independently plausible to me: that naturalism is true, and that transformative psychedelic experiences can have significant epistemic and spiritual benefits. Many who take an interest in psychedelics reject one proposition or the other; I attempted to reconcile them, to dissolve the appearance of inconsistency. But this is only one philosophical problem concerning psychedelics, and only one way to respond. In the next year, three more scholarly books on philosophy and psychedelics are due to be released: an edited volume by Peter Sjöstedt-Hughes and Christine Hauskeller, a monograph by Aidan Lyon, and an edited volume by Philip Gerrans and me. I look forward to seeing these many and varied flowers bloom.

I was also interested by Langlitz’s situating my work in the long history of attitudes to metaphysics. It is true that I see no conflict between a broadly naturalistic methodology and the practice of metaphysical speculation constrained by evidence (“metaphysics naturalized”). It would be interesting, indeed, to see what a post-metaphysical philosophy of psychedelics would look like, given how large metaphysical issues loom in the interpretation of these substances and how frequently their use provokes metaphysical reflection. Some clues are found in Flanagan and Graham’s (2017) arguments that the accuracy of “metaphysical hallucinations” is inessential to their potential roles in promoting mental health and in the good life, as well as Shanon’s (2002) musings about adopting psychedelic-inspired pantheism in a poetic or pragmatic spirit. But none of these authors reject metaphysical questions in principle, and their psychedelic reflections are all defined by a grappling with the metaphysical.

In light of my attempt to reconcile naturalism with the epistemic and spiritual benefits of psychedelic experience, I was gratified to read Nayak’s patient’s description of negative self-related beliefs as akin to a distorting “fun house mirror”. This is a beautifully clear illustration of the psychological mechanism that I see at the heart of psychedelic therapy, and of some of the epistemic benefits this mechanism can have. And, as Nayak says, it demonstrates clearly the independence of this mechanism from metaphysical epiphanies.


Nayak spends some time analysing the scientific research and observes, correctly, that the explanatory relevance of Default Mode Network (DMN) disintegration or downregulation to ego dissolution is not settled. It is, indeed, worth being cautious here; the neurocognitive account in POP is speculative and is intended as a basis for future research. However, the role of the DMN in the account does not rest solely on evidence from psychedelic resting-state studies: a large body of independent evidence links coherent functioning in the DMN and Salience Network to narrative/autobiographical and minimal/embodied forms of self-awareness (Northoff and Bermpohl 2004, Sui and Gu 2017, Koban et al. 2021). The fact that a range of drugs, such as antidepressants and salvinorin A, affect the functioning of the DMN need not undermine a link between this network and self-awareness, since these drugs also alter self-awareness. Indeed, the finding of DMN disintegration under salvinorin A suggests that functional neuroanatomy and neurocognitive theory might be the right levels of analysis to explain what is otherwise puzzling: the phenomenological overlap between the many different drugs that have been called “psychedelic”, despite their neuropharmacological diversity. But, in general, Nayak is correct: nothing here is certain, and many questions remain.

Finally, I entirely agree with Nayak that the non-naturalistic beliefs often formed on the basis of psychedelic experiences result as much from universal, innate psychological tendencies as from variable and contingent enculturation. In this, as in many things, I follow Thomas Metzinger: aspects of our evolved neurocognitive architecture predispose us to have powerful, realistic experiences of apparent non-physical realities, and the default response to such experiences is to believe that they are veridical. To use a wonderful term that Langlitz elsewhere attributes to the psychedelic scientist Felix Hasler, my position is neuroperennialist: I think there is a common core to mystical experiences (as classically defined) that results not from glimpses of a common reality but from the modulation of common, evolved psychological structures. As Hasler puts it: “Maybe the spiritual experiences of human beings do not resemble each other across cultures because they point to the same God or universal truth but simply because human brains all work alike” (quoted in Langlitz 2013, p. 228). Psychedelics show that culturally invariant properties of the human brain predispose us not just to spiritual experiences, but to distinctive kinds of epistemic harms and benefits, in response to pharmacological modulation.


Flanagan, O., and Graham, G., 2017. Truth and sanity: positive illusions, spiritual delusions, and metaphysical hallucinations. In Poland, J., and Tekin, S., eds. Extraordinary Science and Psychiatry: Responses to the Crisis in Mental Health Research, pp. 293-313. MIT Press.

Hales, S.D., 2006. Relativism and the Foundations of Philosophy. MIT Press.

Koban, L., Gianaros, P.J., Kober, H. and Wager, T.D., 2021. The self in context: brain systems linking mental and physical health. Nature Reviews Neuroscience22(5), pp.309-322.

Langlitz, N., 2013. Neuropsychedelia: The revival of hallucinogen research since the decade of the brain. University of California Press.

Mann, T., 2011. Magnificent visions. Vanity Fair. https://www.vanityfair.com/news/2011/12/amazon-201112. 21 June 2022.

Northoff, G. and Bermpohl, F., 2004. Cortical midline structures and the self. Trends in cognitive sciences8(3), pp.102-107.

Shanon, B., 2002. The antipodes of the mind: Charting the phenomenology of the ayahuasca experience. Oxford University Press.

Smith, H., 2000. Cleansing the Doors of Perception: The Religious Significance of Entheogenic Plants and Chemicals. Reprint, Boulder: Sentient Publications, 2003.

Sui, J. and Gu, X., 2017. Self as object: Emerging trends in self research. Trends in Neurosciences40(11), pp.643-653.

Chris Letheby is a Lecturer in Philosophy at The University of Western Australia (UWA) who specializes in the philosophy of mind and cognition. His research to date has focused mainly on the use of classic psychedelic drugs in neuroscience and psychiatry. In several articles and a book, Letheby has argued that a traditional conception of psychedelics as agents of insight and spirituality can be reconciled with naturalism, the philosophical position that the natural world is all there is. His monograph Philosophy of Psychedelics was published in 2021 by Oxford University Press. Follow Chris on Twitter @chrisletheby.

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