Chris Letheby argues in Philosophy of Psychedelics that psychedelics and knowledge are compatible. Psychedelics may cause new mental states, some of which can be states of knowledge. But the influence of psychedelics is largely psychological, and not all psychological processes are epistemic. So I want to build on the distinction between processes of discovery and processes of justification to criticise some aspects of Letheby’s epistemology of psychedelics. Unarguably, psychedelics can elicit processes of discovery. Yet, I hold, they can hardly contribute either to the epistemic success (i.e., truth, veridicality, aptness, skillfulness, etc.) of a mental state or to processes of justification. As these are central for a mental state to be a state of knowledge and are largely uninfluenced by psychedelics, the contributions of psychedelics to knowledge are rather indirect than direct: The heavy epistemic lifting—what turns a mental state into a state of knowledge—is, in its epistemic aspects, independent of any influence of psychedelics on our psyche. Positively, while the mechanisms that Letheby points to need not be associated with knowledge, they do provide crucial epistemic benefits if they are associated with understanding. Reading them as facilitating understanding covers also those cases where truth or justification is missing and thereby provides a broader picture of the epistemic contributions of psychedelics.
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