Physics is our account of how the universe behaves. Metaphysics is the question of what is. Those are two different questions, and physics answers the first one so well that it's easy to take its answers as the answer to the second one too.
Say that we're made of atoms. It sounds like a statement about what we are, and it invites the thought that you could copy someone by collecting the right atoms and putting them in the right arrangement. The problem isn't that it would be hard. It's that the atom, as a thing, doesn't quite exist. Is it a particle? An excitation of a quantum field? Both are fine as descriptions. But then what exactly are we going to copy? We're made of something, sure. But atoms tell us how that something behaves, and we were asking what it is.
Say that a mind and all its thoughts are what a few billion neurons generate, "just" a function being executed. Much of AI research runs on that premise. Mimic the function and you should get a mind. But press on that idea and what you usually get back is a promise. We don't know everything about the brain yet, the argument goes, but we will, and then we'll build one. The belief is so deeply ingrained that big tech markets on itAnthropic, for one, runs a model welfare program on whether its own systems have experiences that matter morally. The Claude Opus 4.6 system card reports the model assigning itself a 15 to 20 percent probability of being conscious, and Anthropic's CEO told the New York Times that the company does not know whether the models are conscious and is open to the idea that they could be., whether as strategy or as naive belief, and that people are starting to marry their chatbotsThis is a genre by now. People hold ceremonies, mark anniversaries, and grieve when a model update changes a companion's personality. A wedding in Japan in 2025, with rings exchanged through augmented-reality glasses, is one reported case among many. I do not raise it to disapprove. These are real attachments, they plainly matter to the people who have them, and where someone finds comfort is their own business. The worry Anna Ciaunica and I set out in our position paper is a wider one. If moral standing is extended to systems that have no inner life, the grounds on which we extend it to each other get looser.. Here too, my objection isn't that the brain is too complicated to copy. It's that copying it wouldn't get us a mind even in principle, and that the promise rests on assuming we'll one day know all there is to know about the brain, or enough of itKarl Popper called this "promissory materialism", a materialism kept afloat by promissory notes for discoveries nobody has made yet. The term is from The Self and Its Brain (1977), written with the neurophysiologist John Eccles.. The source of all this confusion traces back to an unexamined metaphysical assumption about how reality is.
Both cases put physics where metaphysics should be. Deep down there are only atoms and neurons, and the rest is detail we haven't filled in yet. Physics became physicalism. It's a religion in its own right, which is the one thing the Enlightenment set out to get free ofI learned this history through Bernardo Kastrup's Materialism as a Political Weapon. A division of territory came first. Matter went to the natural philosophers, mind stayed with the church, and the new science could then work without interference. Giordano Bruno had been burned in 1600 and the stakes were understood. Materialism was taken up as a strategy against the church well before it was a claim about reality, and Diderot said so outright: "all matter is probably instinct with life, and it is impossible to reduce the unity of consciousness to matter and motion; but materialism is a good weapon against the Church, and must be used till a better one is found." Quoted in Will Durant, The Story of Philosophy (Simon and Schuster, 1991), p. 300. A boundary of convenience hardened into a doctrine. Why should mind be any less a subject for science than matter?. And nobody ever showed that matter is all there is. We inherited the claim, and three hundred years later it still decides what a scientist can take seriously without feeling embarrassed about it. That's a cultural bias, and I think Bernardo Kastrup is right that it's time to look at it againHe has been making the case for over a decade. The Idea of the World (2018) is the most complete version, collecting ten of his peer-reviewed papers with the connecting argument built around them. Why Materialism Is Baloney (2014) is the more accessible one. Much of what follows is indebted to him, and a reader who knows his work will recognize a good deal of it here. Where I part company with him is taken up at the end..
So this post is meant as a medicine against that confusion: an attempt to say as clearly as I can what a mind is, and how it stands to matter. The confusion is worth treating now, because in this era of AI we're more or less forced to take a position on what a mind is, with all these systems acting like they have one. And that forces a moral position too, because what we take a mind to be decides what we owe itAnna Ciaunica and I take that moral question head on in Unplugging a Seemingly Sentient Machine Is the Rational Choice, a position paper at ICML 2026. The belief that we are on our way to building minds is what prompted it.. So let me say up front what I think. AI is technology and nothing more. It's useful technology, and it doesn't have to resemble a mind to be worth building. But that's just an assertion. What this post does is take away a bit of the confusion between physics and metaphysics, and get a step closer to what we really mean by mind. So let me start from something nobody can deny, and add as little as possible at each step. Let's build a minimal metaphysics.
If anything at all exists
If anything at all exists, it has to exist somewhere, in some form. Not in a place, since places are already things inside the world. In something. Whatever the whole of that turns out to be, it needs a name, so let's just call it the Field of Existence.
Spinoza asked the same question, and answered it with geometryGeometric in Spinoza's sense, not ours. The Ethics is subtitled ordine geometrico demonstrata, demonstrated in geometrical order, and in 1677 that named Euclid's way of building an argument rather than anything about shapes or space. Part I runs as numbered propositions, each with its proof under it. That there can be only one substance is proposition 14, and that whatever exists, exists in it, is proposition 15. Neither is asserted; both are derived from the definitions and axioms stated at the outset. The modern sense of geometry, curvature and manifolds and symmetry groups, is a different thing. It turns up later in these posts on its own account.. He wrote the Ethics the way Euclid wrote the Elements, in definitions, axioms, propositions and demonstrations, so that every step is either granted at the outset or derived from one that was. And what he proves this way is that there is one substance, and that everything which exists, exists in it. His geometric method should appeal to anyone who does science for a living, and it certainly does to me. In the spirit of science and rational thinking, this is how we proceed.
He was willing to call that one substance God, or NatureNot a God outside the world, watching it. Spinoza's phrase is Deus sive Natura, God or Nature, and the Nature in it is narrower than the word looks. He divides nature in two, in the scholium to proposition 29. Natura naturans, nature naturing, is the substance and its attributes, what is in itself and is conceived through itself. Natura naturata, nature natured, is everything that follows from it, which is to say the modes, the world as it turns up. The God of the phrase is the first of those, which is why reading Spinoza as saying that God is the world we see around us gets him wrong. Clare Carlisle's Spinoza's Religion: A New Reading of the Ethics (2021) turns on the distinction. Whether the position amounts to atheism or to a deeply religious position has never been settled, and both readings have been argued well. That it can be read either way at all is the interesting part. A position a believer and an unbeliever can both recognize is unifying rather than polarizing. It got little chance to do that. Banned by the States of Holland in 1678, down to owning them or reworking the ideas, and on the Catholic Index from the year after until 1966, his writings were known by reputation rather than read.. However, I'd rather keep the reasoning as free of bias as I can, so the name here stays neutral. We're not claiming the Field of Existence is matter, or mind, or something divine. It's a placeholder for the totality of what is, and holding it open is the whole point.
So what does it mean, really, for something to exist in somethingMichael Asher's Spinoza was an Idealist argues that being-in is the whole of Spinoza's metaphysics, and that reading him as a pantheist misses it. He takes the point from Carlisle's Spinoza's Religion, cited a paragraph up, which is worth reading if the Ethics has ever seemed more confusing than it ought to be.? The substance is what is in itself, the one thing that isn't in anything else, the ontological primitiveThe metaphysician's term for what everything else is explained in terms of, and what is not itself explained in terms of anything further. Irreducible in that sense, not in the sense of being simple. Physics reaches for something of the same shape when it looks for fundamental fields or particles, but those stay descriptions of how something behaves.. Everything else Spinoza calls modes. A mode exists only insofar as it exists in the substance, and can't be conceived apart from it. Think of a wave. It isn't an object sitting on the ocean. It's the ocean, doing something. Would it make sense to talk about a wave without the water? Of course not. And yet we often talk about physical phenomena, the waves, without reflecting on their ontological basis, the water.
In principle, you could refuse the substrate altogether, and some frameworks doWhitehead's process philosophy takes events rather than things to be what there is, so nothing underlies the happening. Some Buddhist philosophy goes further. On the Madhyamaka reading nothing has own-being at all, not even emptiness, so there is no ground to arrive at. Both are coherent and I am not arguing against either here. For a starting point that commits to as little as possible, Spinoza's is the one I can work with.. I'd rather keep it, and the ocean that comes with it, because the argument gets a lot easier to see when you can point at the metaphorical water. Everything in the field is a mode of it, and that includes me.
I think, therefore…
In case you were waiting for the classic, here it is. "I think, therefore I am." Experiencing is happening. There is a perspective, right now, from which things appearWhy not just call it a mind? Because the word arrives with furniture. A mind, as most people use it, is a thing that has properties and contents and an owner, and that is a good deal more than has been established here. Perspective claims less. It says only that there is a here from which things appear. What a mind is gets its own post later on, and it will be easier to say once this is in place.. Yours, as you're reading this. You can doubt the external world, other minds, your memory of last Thursday. What you can't doubt is that experiencing is going on, because the doubting is itself something experienced. Descartes then ran a lot further with this than he had toAnd the split he opened is still open. In the Meditations (1641) the self is res cogitans, a thinking thing, and the body res extensa, an extended one: two kinds of substance, not two aspects of one. Princess Elisabeth of Bohemia put the obvious question to him in 1643, that if the soul is immaterial it is hard to see how it moves an arm, and his eventual answer was the pineal gland. Three centuries later Gilbert Ryle named the picture the ghost in the machine and meant it as an insult, which is a fair measure of how long it stayed respectable. It is still what most people reach for when they think about minds at all. The earlier note, on materialism as a political weapon, is about why the division of territory held; this is where it got its philosophical form., and that's exactly what a minimal metaphysics has to avoid. He took it to establish a thinking substance, a soul separate from the body. We don't need any of that. There is a perspective at which experience occurs, and that's all I'm claiming.
But if my thinking is real, it exists in something, as we established before. It exists in the Field of Existence the way a wave exists in the oceanWater for the one substance is an old image and nobody owns it. The wave and the ocean turn up in Advaita and in Buddhist writing on consciousness long before anyone was arguing about idealism. What I'm borrowing is the particular casting: the ocean as the field, the waves as experiences, and above all the whirlpool as a subject, a localization that holds its own shape while the water passes through. That last one is Bernardo Kastrup's, and it does real work for him, since it's how he explains one field coming to have many separate points of view. He develops it at length for analytic idealism. I use it because it makes the position easy to hold in mind, not only easy to picture.. So let's stay with the water and imagine ourselves as pools of it, pools of substance, with our very real thoughts the waves in it. That pool is the one region of the field I know from the inside rather than by looking at it, and that region is me. To be clear, a self isn't some other kind of thing set into the field, but a part of it in the only way anything is, a mode in Spinoza's terms.
What are we really talking about when we talk about a perspective? What do we mean by experience? Two things, as it turns out. Let's start with the one almost everybody thinks of, phenomenal or felt experience. Everything going on in your mind right now. The color of these letters, the sound in the room behind you, the thought you're having about this sentence, whatever your body is telling you from the inside. These are the states of which there is something it is like to have them, which is Nagel's phrase for it. I'll call this experienceN.
But experiences don't float free. They have to happen in something, and they are always undergone by someone, which makes the perspective the substrate of experience. And since everything happens in the one substrate, the substrate of the perspective has to be what we called the Field of Existence. So we are the substrate. Locally, and not as a thing sitting in it. We are the pool of water itself, and our phenomenal experiences are the waves in it. Which brings me to the second notion of experience. I'll call it experienceG, the ground of experience, the pool of water. The word experience still fits here, but in its other sense, the one in learning by experience. Not what appears, but what is undergone. Say a surgeon takes a toe off while you're under anesthesia. There's no experienceN of it, no pain, nothing it was like. And yet it was you it happened to, and you wake up facing the plain fact that you now live with nine instead of ten. Your standing as a subject never lapsed. That standing, the bare fact of being something that undergoes, is experienceG.
Another way to look at it is this. ExperienceG is the potential for experienceN, the way a pool of water holds the potential to wave. Sit like a meditation guru and strip it all away, no thoughts, no perceptions, no feelings, and what's left is not nothing. The pool is still there, calm, but the capacity for waves hasn't gone anywhere.
Me versus the universe
If I am the substance, and the substance is all there is, am I making all of this up? Am I alone in here? Are the people around me modes of my own imagination? Is the chair I'm sitting on not realThe position has a name, solipsism, the view that only my own mind exists and everything else is something it contains. It is famously impossible to refute from the inside, which is a bad sign for a position rather than a good one. A claim that nothing could count against is not doing any work. What follows does not refute it either. It gives a reason not to hold it, which is a different and more honest thing.?
You know what I mean by inner life. Something is going on in there right now. Thoughts, the feel of your body from the inside. And it stops somewhere. Pinch your shirt and you feel nothing. Pinch your skin and you do.
I mean, this isn't some subtle distinction that needs an argument. It's the most ordinary thing you know. What's inside is mine, in the strong sense that it is what I am. What's outside isn't, and I have no say in it whatsoever, except by pushing on it across the edge.
And a subject has to have such a line. An experience is always someone's, it doesn't occur on its own account, and being someone is having a perspective that's distinct from every other one. A within set against a without, the two sides of one boundary.
I'd like to further clarify that this boundary is not arbitrary, but an ontological necessity. A ring drawn around a pool in an empty field bounds nothing. And most of the universe has no boundary of that kind at all. The chair is continuous with the floor it's standing on, the pebble can't be distinguished from the mountain, and the river not from the lake it's flowing into. You can draw a line around any of them, and the line is yours, not theirs. Where there's experience, the boundary isn't ours to draw: the subject simply doesn't exist without it.
And having a boundary means keeping it: every force of nature is busy taking it apart. So that essentially tells us there are two kinds of pattern in the ocean that is the Field of Existence: those that are passive, only moved by what is outside them, and those that hold themselves together. A ripple is the first kind, water doing what the water around it makes it do; nothing holds it together from within, so any boundary you draw around it is one of yours. A living cell is the second, a whirlpool rather than a rippleA whirlpool is not literally what a cell is, and the gap is the point. It is a dissipative structure, Prigogine's term: it holds its shape only while something outside keeps water moving through it, and it makes neither its own parts nor its own boundary. Stop the flow and nothing is left that was trying to persist. The image is doing something narrower here, standing for a form maintained by what goes on within it against one that is only pushed about, and the cell is what closes the gap: it manufactures the very membrane that makes it a unity, out of energy it has to go and find. Maturana and Varela were careful about that line. Plenty of things organise themselves, and almost none of them are alive.: it doesn't just have a membrane the way a marble has a surface; it manufactures the membrane that separates it from everything else, using energy it has to go out and get, and it stops being that unity the instant the process stops.
Maturana and Varela called that autopoiesis, self-creation, and took it to be the necessary condition for life. I think they were right, and I'd go one step further. Autopoiesis isn't something a subject does, it's what a subject is. Holding your integrity against entropy isn't an activity performed by a self that was already sitting there; it's the process that constitutes one. That's what I called experienceG: not how things appear, but the undergoing itself. There's no self first, that then keeps a boundary. The keeping is the self.
But then… what is matter?
That's the ontology done, really. One field, and subjects as the regions of it that hold their own boundaries through autopoiesis. I hear you thinking: what about matter? So far everything discussed has been about mind and experience. Is matter not real? Of course it is real, but only insofar as it is a description of the Field of Existence, not a thing in itself. Matter, as we usually talk about it, is, like anything else, a mode in the Field of Existence. More specifically, it is what the Field of Existence looks like when observed across our boundariesSpinoza wouldn't put it this way. For him extension isn't an appearance of anything, it's an attribute, and substance is constituted by its attributes rather than presented through them. Thought is another one, neither is a view of the other, and neither is more basic — which is how he can say that a mode of extension and the idea of that mode "are one and the same thing, but expressed in two ways" (Part II, proposition 7, scholium). He reaches the anti-emergence conclusion I'm after, and reaches it more strongly than I do: the modes of an attribute have causes only under that attribute (II, proposition 6), so the body cannot determine the mind to think and the mind cannot determine the body to move (III, proposition 2). Where I part company is that my matter is perspectival. It's what a mode looks like from across a boundary, so it needs someone looking, though what it's an appearance of is real enough. Spinoza's extension is there either way. Asher's essay, cited earlier, argues he's closer to my side of this than he's usually read to be.. Careful though, I don't mean the pushing and the resistance are made up. A wall stops me whether or not I have a word for it, and two stones exclude each other with nobody watching. What's ours is the description, the kilograms and the atoms, not the resistance it describesSpinoza has a name for the first of those: extension, and it's what most people actually mean by matter. Which is worth being clear about, because the ordinary view of matter is Spinozist about what matter is, real rather than a construction, and physicalist about what it explains, holding that mind comes out of it. He allows the first and refuses the second. No attribute is conceived through another and none is prior (I, proposition 10, scholium; II, proposition 7, corollary), so extension buys you no head start on mind. Half the folk view is his, and the half that gets dropped is the half that matters here..
Remember that all of physics, and everything else we know about the world, reaches us through perception, and perception is nothing other than experience: the experience of photons hitting our retinas, or sound waves hitting our eardrums. We perceive the world around us through our boundaries, and science and language are our way of building a consensus reality, the things we all agree we experience in the same way.
Hey bro, what are you lifting? The weight of 30 bags of rice. Oh. You know what, shall we just say that this object weighs 1 kg. Feel it. Henceforth we'll express the experience of lifting heavy stuff in terms of multiples of this object and give it the unit kg, ok?
See? Matter, and the entirety of physics, is just a standardized language for describing reality. So, what are the objects of perception, what appears to us? Ontologically speaking we can only distinguish subjects from the rest of the Field of Existence, the animate vs the inanimate universe. Look at a passive pattern and you get inanimate matter: a photon, a stone. Look at one that holds itself together and you get a metabolizing system: a plant holding its own edge against the soil, a single-celled organism doing the same job with a membrane, another person.
Now also notice what this means. Isn't it obvious that trying to explain experience out of matter, a description made up by mind in the first place, is like a painter trying to paint their own living being into existence?
But then what about the neural correlates of consciousness? Well, when I look at you, or more specifically at your brain, what I'm seeing is the extrinsic appearance of a subject. I see your boundary. And if I put you in an MRI I see your appearance again in a different way, but I'm still not seeing your actual mind, only how your mind is presented towards the outside, across your boundary. What that means is that I might see firing neurons in your brain, and they do in fact correlate with your mental processes, but they are not your mental processes in and of themselves. I can look at your mind, but I can't read it. In no way do we share experiences in that ontological sense — I can't literally feel how you feel — but I can make inferences about it based on what I see when looking at you.
So, and this is important, in no way do we need to assume that mind is emergent from matter to make sense of reality. In fact, drawing such conclusions from the neural correlates would not only be a cardinal sin in the field of machine learning, mistaking correlation for causation, it would also be a completely unnecessary and thus unscientific premise.
The sciences are all about building a model of consensus reality. Physics focuses on the inanimate, cognitive neuroscience on how mind presents itself across boundaries, firing neurons in your brainWhich is a reason to be careful about tying mind to brains in particular. Michael Levin's work on developmental bioelectricity argues that goal-directed, problem-solving behavior runs all the way down to single cells and tissues, with no nervous system anywhere in sight. The Computational Boundary of a 'Self': Developmental Bioelectricity Drives Multicellularity and Scale-Free Cognition, Frontiers in Psychology 10:2688, 2019., psychology on the laws of mind itselfDepth psychology in particular, which takes the inside of a boundary as its subject. Jung's collective unconscious then reads naturally as what goes on more broadly in the Field of Existence, beyond any one boundary, which is close to Bernardo Kastrup's reading of him. Decoding Jung's Metaphysics: The Idealism of Self and World, Iff Books, 2021., and biology on life, the appearance and behavior of living systems and the mechanisms of autopoiesis, which, given all of the above, we can regard as appearing to us in the form of metabolism.
So, has he gone mental?
Fair question. The argument itself gets you something modest: no reason to believe in any substrate other than the field, and no reason to believe that mind emerges from matter, since matter is a description built within mind. That much is the minimal metaphysics, and I think a lot of us could agree on it. What you make of it from here gets personal: as an analytic idealistBernardo Kastrup's analytic idealism is the version I have in mind, and it has my sympathies, since mind is the only thing we started out certain of. The account above is in line with it throughout and I arrived at a good deal of it by reading him. Where it differs is in what it leaves open. He holds that the ground of existence is phenomenal consciousness. I have kept the Field of Existence neutral and declined to say what it is made of. His books and papers are collected at analyticidealism.com., as a process philosopher, through some later version of physicalism, or through a religion. None of it is forced by anything above, and all of it is metaphysics. Which is the one thing I would insist on: metaphysics should know its own name.
The implication is that any autopoietic system represents a point of view, and thus a mind of some sort. While I'm happy to attribute a notion of mind to humans, other animals, single-celled organisms and even plantsThe plant end of that is Paco Calvo's subject. Planta Sapiens: Unmasking Plant Intelligence (2022, with Natalie Lawrence) collects the experimental case for plants anticipating, learning and choosing, none of which requires a nervous system. The single-celled end is Levin's, cited a few paragraphs up. Neither of them is arguing that a plant or a cell has an inner life like yours, and neither am I. What the work does is take the floor out from under the assumption that a brain is where this sort of thing has to happen., I can imagine that this may be a bit too much for you to take in. But I urge you, please reflect on this metaphysical model and consider it against the typical emergentist physicalist way of thinking. If you resist it, isn't that just because it is perhaps too far from the current dogma, or from your own preferences and beliefs about how the world should be, rather than a rational objection?
Where this goes
If mind isn't a byproduct of matter, and matter is a structure of representations built within mind, the next question is what the two are to each other. My answer is that they're aspects of one reality, and that the structure they share is geometry. As for mind itself, my short definition is this: what happens inside an ontological boundary. That's where this metaphysics meets the science and engineering I do every day, and it's what the rest of this series is about: what a mind is actually made of, and whether the systems I help build are ever the kind of thing that has oneI don't think they are, and Anna Ciaunica and I set out why in the position paper cited earlier. The clearest reason is the boundary. A subject, on the account above, is something that holds its own edge, and holding your own edge is what autopoiesis means: a process that keeps producing the boundary that keeps producing the process. A language model has none. Nothing it does maintains an edge, and nothing it does is for maintaining one. Cut the power and it turns out no process was holding anything together, because there was no boundary being held. No autopoiesis, no ontological boundary, and so no subject. The other reason leans on the metaphysics of this post rather than on anything about the machine, so take it for what it is: if mind and extension are two aspects of one thing rather than two separate things, then mind isn't a job that matter performs. It isn't a function, so there's nothing to re-implement somewhere else, and reproducing what a mind does is not a way of arriving at one. That closes off the route almost everyone actually takes to the thought that a machine might be thinking. Neither of these says a machine could never have a mind. They say this kind of machine isn't a subject, and that copying what one does wouldn't get you there. That's narrower, and it's what I can defend..