‘Philosophy of Psychedelics’ Book Forum: Part Three

Nicolas Langlitz reviews Philosophy of Psychedelics (Oxford University Press, 2021) by Chris Letheby.

This is Part Three 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 Four by Sandeep Nayak, click here.

For Part Five by Chris Letheby, click here.

What Is Philosophical about the Philosophy of Psychedelics?

The Rise of Psychedelic Humanities

The revival of psychedelic research began in the 1990s and initially focused on basic neuroscience and preclinical psychiatric research (Langlitz 2012a). The 2010s introduced two new threads into psychedelic studies: clinical trials as well as social research and humanities scholarship. The clinical trials have moved psychedelic drugs to the verge of their formal introduction into Western medicine and thus society. Deliberating on their place in late modern societies is the job of philosophers, literary theorists, historians, sociologists, anthropologists, and science & technology studies scholars. Only a few years ago, it wasn’t at all self-evident that these substances could be objects of legitimate research in medicine and the biosciences and certainly not in other fields. In 2013, however, Neşe Devenot called on her fellow humanists to get involved in the psychedelic revival. In 2016, I wondered out aloud whether there was a place for psychedelics in philosophy (Devenot 2013; Langlitz 2016). Five years later, this question can be answered in the affirmative. Chris Letheby’s Philosophy of Psychedelics is not the first philosophical engagement with psychedelics but the most impressive in this budding subfield of the philosophy of mind. Its publication marks the entwinement of a rapidly growing clinical literature with the birth of psychedelic humanities.

Letheby’s book uses the tools of neurophilosophy to theorize the transformative potential of psychedelics, which psychedelic-assisted psychotherapy harnesses for clinical purposes. Although I have been following the neuropsychopharmacological literature on this class of drugs for two decades now, the way Letheby synthesizes it with the most recent philosophy of mind offered more than one eureka to me. Part of me read the book for its insights into the nature of the psychedelic experience. But I also read Philosophy of Psychedelics as an anthropologist of knowledge cultures who observes how other observers observe the world and who has conducted ethnographic work on neurophilosophy before (Langlitz 2015a, 2015b). Hence, my review will render the epistemic medium of Letheby’s observations “opaque,” to use his terminology. Instead of looking through his transparent lens at the object of study to assess whether his claims about psychedelics are true or false, I will focus on the neurophilosophical lens enabling these truth claims in the first place. The question behind my reading is how Letheby situates philosophy in the revival of psychedelic research. What role is it coming to play in a field that has been dominated by biomedical sciences?

A Naturalist Philosophy of Psychedelics

The title of Letheby’s book misses an indefinite article: it does not offer the philosophy but a philosophy, a naturalist philosophy of psychedelics. Letheby presupposes that the natural world is the only reality there is and, if users of psychedelics experience a transcendental universal consciousness or other kinds of disembodied minds and supernatural forces that escape the natural sciences, as a matter of principle they suffer from metaphysical hallucinations (3, 28).

The anthropological and historical archives suggest that a naturalist perspective is not the only one humanly possible. There is a rich literature on the uses of psychedelics in animist cultures where shamans take the drugs to communicate with nonhuman entities such as spirits. Western psychedelic culture has given rise to a form of neoanimism, in which Euro-Americans communicate with psilocybe mushrooms as if they were human (Steinhardt 2020). Aldous Huxley’s famous essay The Doors of Perception introduced a whole generation of counterculturalists to the idea that psychedelics enabled a communion of an individual’s mind with a cosmic “Mind at Large” (Huxley 1990[1953], 23-24). The ethnological view from afar notes that Letheby’s philosophy of psychedelics counters these alternative interpretations and contributes to a reconstruction of the naturalist cosmology that dominates how modern Europeans, North Americans, and Australians understand the world (Descola 2013). In the revival of psychedelic research, such reconstruction is necessary because many users of psychedelics resurface from their trips to the antipodes of the mind with the firm conviction of having encountered a transcendent reality that outshines this one.

While neurophilosophers sometimes suggest that their reference to scientific knowledge helps eliminate competing metaphysical schemes (Churchland 1986), a belief that Letheby at least entertains, the sociological truth of the matter is that after two and a half millenia of controversy no agreement about metaphysics has emerged and Letheby’s naturalism remains a contingent and contentious position (although one I happen to share when I doff my pith helmet as ethnographer and don the hat of amateur metaphysician). While his metaphysical commitment aligns with the dominant view in the philosophy of mind today, he also recognizes that non-naturalist views such as idealism and panpsychism have recently been making a comeback and that philosophical metaphysics is a highly contested field (28, 37, 214). Even within academic philosophy, the love of wisdom does not progress toward a consensual and coherent body of knowledge but continues to be organized by dissent over alternative ways of understanding the world and the human place in it.

Philosophy, Not Science of Psychedelics

The problem of metaphysics is key to understanding how Letheby conceives of the contribution of philosophy to psychedelic research. With reference to scientists who declare that determining the truth value of their test subjects’ metaphysical experiences was “above their pay grade,” Letheby notes: “For better or worse, as a philosopher, this question is not above my pay grade: it is right there in the job description.” (30) As a neurophilosopher and self-identified methodological naturalist who “sees philosophy as continuous with the natural sciences” (36), he refrains from putting more emphasis on this divergence from scientific empiricism, but that is where Letheby’s philosophy of psychedelics sets itself apart from psychedelic science.

Note that the way Letheby describes his job as professional metaphysician is just as controversial as the particular metaphysical position of naturalism that he maintains. In 20th-century philosophy, a broad alliance bringing together otherwise conflicting schools of thought ranging from logical positivism to Critical Theory and neopragmatism had eliminated metaphysics from their office manuals. Since there was no way of empirically verifying or falsifying metaphysical statements, Rudolf Carnap (1959[1932]) contended, they could neither be true nor false but were simply meaningless. Although it would have been too much of a digression for Letheby’s book to not only lay out a philosophy of psychedelics but to also recount the revival of metaphysics in analytic philosophy, he provides some insights in how he thinks about this crucial question. His brand of neurophilosophy has long moved beyond the positivist reliance on observation sentences and recognizes that “our total sensory evidence is consistent with any number of metaphysical schemes.” (126) In Letheby’s eyes, this underdetermination of metaphysical theories by evidence does not make nonsense of metaphysics. Instead, he practices metaphysical speculation constrained by and consistent with the scientific evidence. That is one way to comport oneself as philosopher, although very different from, say, Jürgen Habermas’s (1992) or Richard Rorty’s efforts to inform postmetaphysical thought. Perhaps Letheby figured that Rorty (1989: xvi) was mistaken when he surmised that a postmetaphysical culture was no more impossible than a postreligious one, and just as desirable.

Socrates blotter art. Photoshopped by author.

Looking Back at Letheby 2020 from 2070

A philosophy that aspires to be continuous with the sciences confronts its practitioners with the same problem that sociologist Max Weber (2004[1919]: 11) first identified a century ago for the pursuit of science as a vocation: “We all know that what we have achieved will be obsolete in ten, twenty, or fifty years. That is the fate, indeed, that is the very meaning of scientific work.” Students who choose a career in the sciences must resign themselves to the medium-term insignificance of their research. Letheby is cognizant of this existential challenge to neurophilosophy as a vocation: “Psychedelic science is a fast-moving field, and this book will be out of date in some respects before it hits the shelves—which is a good thing.” (7)

The acceleration of scientific advances has dragged neurophilosophy with it into the maelstrom of dehistoricization. When Patricia Churchland (1986) brought the field to prominence, she still tied her project to Aristotle, Hume, and the Vienna Circle (Langlitz 2012b). A look at Letheby’s bibliography suggests that the vast majority of his citations refer to texts published between 2000 and 2020 (with a few references to first-wave psychedelic science from the 1950s and 1960s and even fewer references to classics of 20th-century analytic philosophy such as Bertrand Russell or Wilfred Sellars). Philosopher György Márkus (1987) argued that philosophy and other humanities differed from the natural sciences in their citation patterns, which in turn pointed to very different temporal horizons. The style of philosophy he had in mind referred to centuries- and sometimes millenia-old classics to mark long-standing oppositions and organize the field in a polemic-dissensive manner. I followed Márkus’s account when I imagined a possible role of psychedelic humanities in the revival of psychedelic research (Langlitz 2019).

Although the tone of Letheby’s Philosophy of Psychedelics is hardly polemic and not anchored to canonized texts, he develops his argument in opposition to competing standpoints in contemporary philosophy of mind. Thus, Márkus’s account of philosophy as an inherently agonistic field remains pertinent. It suggests that the conflictual quality of philosophical positions plays a significant role in their long-term survival in the citational economy. The question is whether Letheby’s book will still be read in 2030, 2040, or 2070 because of its genuinely philosophical merits. Maybe because it fields naturalism against idealism or panpsychism?

But Letheby’s survival strategy might be more conciliatory than combative. He invites readers unpersuaded by his naturalism to treat the book as a “conditional exercise in seeing how much sense can be made of psychedelic phenomena within naturalistic constraints.” (33) His own answer to this question is that “there is a surprising amount of common ground between naturalistic and non-naturalistic accounts of the psychedelic state. The former can endorse many of the distinctive and typical claims of the latter, suitably interpreted.” (220) Letheby might be read beyond the scientific best-before date of his philosophical work not as a soldier of naturalism but as a metaphysical peace broker.


Carnap, Rudolf. “The Elimination of Metaphysics Through Logical Analysis of Language.” In Logical Positivism, edited by Alfred Jules Ayer, 60–81. Glencoe (IL): The Free Press, 1959 [1932].

Churchland, Patricia S. Neurophilosophy: Toward a Unified Science of the Mind-Brain. Cambridge (Mass.): The MIT Press, 1986.

Descola, Philippe. Beyond Nature and Culture. Chicago: University of Chicago Press, 2013.

Devenot, Neşe. “A Declaration of Psychedelic Studies.” In Breaking Conventions: Essays on Psychedelic Consciousness, edited by Cameron Adams, Anna Waldstein, David P. Luke, Ben Sessa, and David King, 184–95. London: Strange Attractor Press, 2013.

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Langlitz, Nicolas. Neuropsychedelia: The Revival of Hallucinogen Research since the Decade of the Brain. Berkeley: University of California Press, 2012a.

— “Aristotelian Neurophilosophy for Big Children.” BioSocieties 7, no. 1 (2012b).

— “On a Not So Chance Encounter between Neurophilosophy and Science Studies in a Sleep Laboratory.” History of the Human Sciences 28, no. 4 (2015a): 3–24. https://doi.org/10.1177/0952695115581576.

— “Vatted Dreams: Neurophilosophy and the Politics of Phenomenal Internalism.” Journal of the Royal Anthropological Institute 21, no. 4 (2015b): 739–57. https://doi.org/10.1111/1467-9655.12285.

— “Is There a Place for Psychedelics in Philosophy? Fieldwork in Neuro- and Perennial Philosophy.” Common Knowledge 22, no. 3 (2016): 373–84. https://doi.org/10.1215/0961754X-3622224.

— “Psychedelic Science as Cosmic Play, Psychedelic Humanities as Perennial Polemics? Or Why We Are Still Fighting over Max Weber’s Science as a Vocation.” Journal of Classical Sociology 19, no. 3 (August 1, 2019): 275–89. https://doi.org/10.1177/1468795X19851405.

Márkus, György. “Why Is There No Hermeneutics of Natural Sciences? Some Preliminary Theses.” Science in Context 1, no. 1 (1987): 5–51.

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Steinhardt, Joanna. “Teachers, Friends, Allies: What Do We Make of Psychedelic Animism?” Cultural Anthropology Hot Spots (blog), July 21, 2020. https://culanth.org/fieldsights/teachers-friends-allieswhat- do-we-make-of-psychedelic-animism.

Weber, Max. “Science as a Vocation.” In Max Weber. Vocational Lectures, edited by David Owen and Tracy B. Strong, translated by Rodney Livingstone. Indianapolis: Hackett Publishing Company, 2004.

Nicolas Langlitz is an Associate Professor and Chair of the Department of Anthropology at The New School for Social Research in New York. He studies the knowledge cultures of behavioral sciences such as neuropsychopharmacology and primatology.

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