Before anyone was doing philosophy in the Western academic sense, human beings were using altered states of consciousness as tools for asking the biggest questions. The Eleusinian Mysteries, a ritual initiation conducted annually in ancient Greece for nearly two thousand years, almost certainly involved the ingestion of a psychoactive brew. Plato attended. So did Aristotle, Marcus Aurelius, and Cicero. Initiates reported experiences of death and rebirth, of seeing reality in a completely new way, of coming into direct contact with something they could only describe as divine.
The classicist Carl Ruck and psychedelic researcher Albert Hofmann (who synthesized LSD) proposed in The Road to Eleusis (1978) that the kykeon, the ritual drink of the Mysteries, was likely an ergot-based psychoactive preparation. Whether or not this specific hypothesis is correct, the historical record is unambiguous that many of the intellectual and spiritual traditions that shaped Western civilization regarded carefully managed altered states as a genuine route to knowledge, not merely entertainment or escapism.
Fast forward to the 20th century and a strange thing happened. Aldous Huxley took mescaline in 1953 and wrote The Doors of Perception, in which he proposed that ordinary consciousness is a kind of reducing valve, the brain does not produce consciousness so much as it filters and narrows it, to prevent us from being overwhelmed by the full range of what is actually there. Psychedelics, on his view, temporarily turn down the gain on the reducing valve, allowing more reality through. The resulting experience feels like an encounter with a broader, more vivid, more intrinsically meaningful world.
This is a genuinely philosophical hypothesis. It is not simply the claim that psychedelics feel intense and strange (which is undeniable). It is a claim about the normal functioning of consciousness, that our ordinary, sober state is already a highly filtered, highly selective, pragmatically constrained version of what experience could be. The drug does not create something new; it removes a filter.
The neuroscientist Robin Carhart-Harris has developed a contemporary version of this hypothesis called the entropic brain theory. Ordinary consciousness, he argues, is organized around high-order default-mode-network activity: the brain's tendency to run familiar, predictive models of the self and world, suppressing information that doesn't fit. Psychedelics dramatically reduce activity in the default mode network, increasing "entropy" in brain states, allowing more unusual, less predictable patterns of neural activity. The experience of ego dissolution that many people report on high doses is, on this account, the temporary disorganization of the brain's usual self-model.
This is not just psychopharmacology. It is relevant to some of the deepest questions in philosophy of mind: What is the self? Is it a construction or a discovery? What is the relationship between the brain's models and the reality they model? And if the "normal" self is a simplification produced by a filtering process, what does that imply about the metaphysics of ordinary experience?
Quick reflection
Huxley's reducing valve hypothesis says ordinary consciousness is already a highly filtered version of what experience could be — the brain narrows experience to make it practically manageable. Does this resonate with anything in your experience? Think about times you've been absorbed in music, in nature, in flow states, in meditation — have you ever had the sense that ordinary filtering had been loosened, without any drugs being involved? What does that suggest?