For a long time the mind–body problem seemed fairly straightforward to me. Not straightforward to solve — straightforward in the sense that the menu looked short. Physicalism says consciousness arises somehow from physical matter, ultimately from brains. Idealism turns the arrow around: consciousness is fundamental, and the physical world we encounter is something closer to a representation within mind. Two options, pointing in opposite directions, and you pick the one that fits what you think you know.

Of the two, idealism always felt considerably more intuitive to me. Part of the reason is undoubtedly psychedelic experience, and that admission immediately creates a problem, because experiencing something doesn't establish that your interpretation of the experience is true.

This is worth stating plainly, because the failure mode here is so common. A DMT entity can seem more independently real than the person sitting next to you. A mystical experience can arrive with a sense of certainty that ordinary life never produces — what William James called the noetic quality, the conviction that one has encountered knowledge rather than merely had a feeling. You can experience the dissolution of the self, meet apparently autonomous intelligences, or become utterly convinced you've glimpsed the structure underlying reality. But that conviction is itself part of what the drug produces. A state that reliably generates certainty is the last state whose certainty you should take at face value. Phenomenological certainty isn't metaphysical evidence.

What interests me is that accepting this hasn't pushed me back towards physicalism. It's made the map considerably stranger.

Maybe the question is wrong

The familiar version asks how matter produces mind, and on the evidence, matter obviously has something to do with it. We can map neural activity with increasingly ridiculous precision. We can watch anaesthetics extinguish consciousness and restore it. Psychedelics radically reshape experience by altering what's happening in the brain. Damage a small piece of tissue and an entire aspect of someone's experienced world can vanish — not their ability to talk about it, but the thing itself. Brains matter.

None of that touches the strangest question, which is why any physical process should feel like anything from the inside.

This is the point Leibniz made three hundred years ago and nobody has answered since. Imagine the brain expanded to the size of a mill, he said, so you could walk around inside it. You would see parts pushing other parts, and nowhere would you find a perception. The observation hasn't aged. We have replaced his gears with synapses and neurotransmitters and we can now watch them in extraordinary detail, but the structure of the puzzle is untouched: you can describe every mechanical relation in the system and the experience is still not among the things you have described.

The usual response is that consciousness emerges from all that activity. But "emergence" names the gap rather than crossing it. In every other case where we use the word, the higher-level property turns out to be a pattern of lower-level behaviour and nothing more. Liquidity just is the disposition to flow, to wet things, to take the shape of a container — explain the molecular behaviour and there is no residue left over. Explain every behaviour associated with pain and there is still, apparently, the fact that it hurts. The analogy holds only if consciousness is a behavioural property like liquidity, which is precisely the thing in dispute.

So I'd rather sit with a different possibility. Perhaps matter doesn't produce consciousness. But perhaps consciousness doesn't produce matter either. Perhaps both are manifestations of something more fundamental than either.

The question mark underneath reality

This is roughly the territory of neutral monism, a position associated with Russell and with James before him. Rather than starting from two fundamentally different substances and then struggling to explain how they touch, it proposes that both arise from an underlying reality which is intrinsically neither — at least not in the sense we normally mean by those words.

Set out schematically, the three positions look like this:

Physicalism: Matter → Consciousness

Idealism: Consciousness → Matter

Neutral monism: ? → Matter, ? → Consciousness

Russell's route into this is worth following, because it isn't mystical in the slightest. Physics, he pointed out, tells us only about the structure of the physical world: what it does, how it relates, what it's disposed to do under given conditions. It says nothing whatsoever about what matter intrinsically is. That isn't a gap in current physics that better instruments will fill. It's what a physical theory is: a formalism of relations. And we happen to be acquainted with exactly one piece of reality from the inside rather than relationally, which is our own experience. Whatever occupies that question mark, in other words, isn't an exotic addition to the world. It's the one thing the scientific description was never designed to reach.

The mind–body problem then looks different. We may be trying to explain the relation between two things that aren't separate at the level where the explanation would live.

That still leaves the question mark, and there's a further possibility lurking behind it: that creatures like us may not be equipped to conceptualise whatever belongs there.

This isn't a retreat into mysticism — it's an argument about cognitive limits, and something like it has been made carefully by Colin McGinn. Human cognition evolved in a specific environment, handling objects of a particular size, at particular speeds, over trivial stretches of cosmic time. There's no obvious reason evolution should have furnished a primate with an intuitive grasp of the fundamental architecture of reality, any more than it furnished us with an intuitive grasp of quantum mechanics, which we manage only by abandoning intuition for mathematics. Every other animal has concepts it cannot form. It would be a remarkable coincidence if we happened to be the one species whose conceptual repertoire exhausted what there is.

Asking us to comprehend it may be like asking a dog to understand constitutional law. The dog isn't stupid. Constitutional law simply isn't part of the cognitive world evolution prepared it to inhabit.

And then there are the entities

This is where psychedelics make the philosophical problem genuinely interesting, and it's worth setting aside the obvious question to get at a better one.

Forget, for a moment, whether psychedelic entities are "real". That's precisely what we cannot settle from the experience itself. Ask something else instead: what kind of universe would have to be the case for them to be real?

Aliens, by comparison, are easy. A craft could land tomorrow carrying six-legged creatures from another solar system and physicalism would barely register the event. They're organisms. They evolved somewhere. Their nervous systems produce consciousness by whatever means ours do. An extraordinary discovery, and almost entirely mundane metaphysics.

What people report in profound psychedelic states is conceptually different. The apparent intelligences aren't typically experienced as organisms living elsewhere in our universe. "Elsewhere" often feels like the wrong category altogether. No planet, no craft, frequently no body, and sometimes not even individuality in anything resembling the human sense.

That's a much stranger proposition than extraterrestrial life: could consciousness exist in forms that aren't instantiated as biological organisms within the physical reality available to us?

I don't know. More to the point, having experienced something that felt exactly like that doesn't mean I know. But I've come to want a philosophy of consciousness that at least leaves the question open rather than ruling it out by definition before the evidence is in.

Two questions people tend to muddle

There's a thought experiment that separates them cleanly.

Suppose we discovered conclusively tomorrow that extraterrestrial life doesn't exist — that Earth is the only planet in the observable universe on which biological consciousness ever developed. Would it follow that humans are the only conscious beings there are?

Under physicalism, something close to that conclusion does follow. Consciousness requires the right kind of physical system; no other such systems exist; the matter is closed. But under idealism, neutral monism, cosmopsychism or the more transcendent accounts, it doesn't follow at all. There could be no aliens whatsoever while reality nonetheless contains forms of consciousness entirely unlike ours. And the reverse holds just as well: the universe could be crawling with extraterrestrial civilisations while every psychedelic entity anyone has ever met is generated wholly by human brains.

They're independent questions, with independent answers, and I'd previously run them together.

The useful lesson may be the uncertainty

Five days ago, asked which metaphysical position was closest to mine, I wrote that idealism seemed nearest — that I tended towards consciousness being fundamental rather than produced by matter.

Someone replied by asking whether experiencing something proves that it exists.

It doesn't. And annoyingly, it's a very good question, because after several more days of thinking about it I'm no longer confident about the first sentence I wrote. Consciousness might well be fundamental. But there might equally be something underneath both consciousness and matter, something for which our distinction between "mental" and "physical" is itself the wrong instrument — two categories available to creatures standing on this side of it, being asked to do work they were never shaped for.

Psychedelic experience hasn't given me an answer to the mind–body problem. Studying the philosophy properly is doing something more useful than that. It's making the question much bigger, and making me suspect that the difficulty isn't only that we lack the answer, but that we may not yet be asking in a form that could have one.