The Varieties of Psychedelic Epistemology, Chris Letheby, 2019

The Varieties of Psychedelic Epistemology

Chris Letheby

Published in N. Wyrd, D. Luke, A. Tollan, C. Adams, and D. King (eds.) : “Psychedelicacies: more food for thought from Breaking Convention“, Strange Attractor Press, 2019.



Is it possible to gain knowledge1 by taking psychedelic2 drugs? One influential answer is ‘yes’: according to this conception, by inducing mystical states of consciousness, psychedelics afford direct knowledge of supernatural, transcendent dimensions of reality. This is an entheogenic conception of the drugs as agents that “generate the divine within”. A second influential answer is ‘no’: since materialism or physicalism3 is true, there are no transcendent realities, and psychedelics just cause compelling hallucinations or delusions. This is a psychotomimetic or hallucinogenic conception of the drugs as psychosis-mimicking or hallucination-generating agents whose essential effects are anti-epistemic4; far from facilitating knowledge gain, psychedelics actively hinder it.

A third, relatively unexplored view is that psychedelics can afford genuine epistemic benefits, even if materialism is true and there is no transcendent reality. From this perspective, the drugs’ epistemic credentials do not depend on the existence of anything supernatural. Rather, psychedelics can afford genuine and sometimes transformative insights of a kind compatible with physicalism.
Several authors have recently made proposals along these lines. Here I offer a taxonomy and critical review of these proposals using standard categories from epistemology, the philosophical study of knowledge. This is intended as a contribution to the “progressive initiative to demystify the psychedelic experience” being pursued by Carhart-Harris and colleagues (Carhart-Harris et al. 2018).

While it is possible that psychedelics afford propositional knowledge gain, I suggest the most promising idea is that they offer new knowledge of old facts (Gertler 1999). Rather than helping us learn new factual information, psychedelics allow us to understand or appreciate already-known (or otherwise knowable) facts in deep, vivid, affectively and motivationally significant ways.

Some authors have tried to refute the very idea of psychedelic-assisted knowledge gain. Roche (2010) argues that psychedelics impair the operation of brain mechanisms whose function is to represent reality accurately. It is highly unlikely, he says, that such impairment would lead to epistemic benefits. But in this dialectical context, the claim that “impairment” is psychedelics’ only or most important effect is question-begging. Certainly some of their paradigmatic perceptual effects are misrepresentational, as when they cause subjects to perceive stationary objects as moving (e.g. the phenomenon of ‘walls breathing’). But the question at issue is whether some of their various effects on cognition and perception might be epistemically beneficial, even though others are detrimental or neutral. Looking through a telescope impairs one’s ability to perceive near objects accurately, while improving one’s ability to perceive distant objects accurately. Some practices and technologies that affect humans’ epistemic capacities improve them in one domain despite impairing them in others (Bortolotti 2015).

Another sceptical argument is as follows: for any putative drug-induced (or altered-state-induced) knowledge gain, either we can verify it independently or we cannot. If we cannot, then we have no reason to trust it; and if we can, then the drug (or altered state) is redundant, since we could have obtained the knowledge anyway (cf. Windt 2011)

One possible response is to suggest that we might independently verify a method of learning about a certain type of fact, obviating the need to verify independently each specific fact learned by that method. For example, suppose that certain findings about psychedelics’ neurocognitive effects, combined with independent evidence about the functional architecture of the brain, support the following claim: psychedelics promote accurate and unbiased introspection of hidden or repressed desires and motivations. In that case, we could adopt a general policy of trusting psychedelic-assisted introspection of this kind, without needing independent verification of each of its individual deliverances. A second possible response would be to concede the point regarding factual or propositional knowledge, but hold that psychedelics afford access to other kinds of knowledge, discussed further below.

In any case, I do not think that a priori master arguments can establish the existence or otherwise of psychedelic-assisted knowledge gain. Rather, we must consider specific proposals about psychedelic epistemology individually, on their own merits, in light of the best available evidence.