Something can change continually and still maintain an identity, can't it? In fact, isn't that what every compound being is doing? — Wayfarer

In so far as hammer XYZ remains hammer XYZ and does not become dolphin ABC because we identify it as such because of its material arrangement and spatiotemporal coordinates, maybe yes. Hammer XYZ at time t and hammer XYZ at t+1 (it did not move positions) are only different in that they are at another point in time. If we assume the passing of time does not kill identity, hammer-XYZ(t) and hammer-XYZ(t+1) are the same. But what if it moved? They now have yet another difference, besides temporal distance: spatial difference. Let's say it also does not destroy identity. What keeps identity? Maybe the material composition of the hammer.

Now, if we took "one atom of wood" from the hammer and replaced it with another atom of wood second by second, in such a way that eventually all atoms were replaced. I believe most people would say it is still the same hammer. How is that so? We must find something that makes them the same. I struggle to find one single thing that establishes identity with hammer-XYZ at the beginning and at the end of the atomic replacement. If anything, it must be that both are the object of this action of atomic replacement. But then that would make it no different from another hammer which also undergoes the same process at another place and time. Even if another identical hammer underwent the exact same process in the same space but at another time, they would not be the same hammer if that hammer does not ultimately come from the original hammer. It seems that spatio-temporal continuity is an important part of identity. Moreover, we also identify hammer-XYZ(t) and hammer-XYZ(t+1) as the same because it is useful to do so.

But then we turn the attention to the thing that identifies, the thinking being. It is a common debate whether the person coming out of the teleportation machine is the same as that that walked in or if it is someone else with the exact same memories, as the spatio-temporal continuity is broken. When it comes to consciousness, is it not interrupted temporally (and spatially as well technically) when we go to sleep? You could argue that consciousness does not fully cease once you go to sleep, but only when your brain dies and thus you as well.

Therefore, even if time is discrete/discontinuous, should we believe that the person walking into time t+1 and the person walking out of it are the same? Is there really such a thing as spatio-temporal continuity in discrete time, and is it enough to account for identity?

If Buddhists are asked whether the person who is born as a consequence of past karma is the same as the person in the previous existence that generated said karma, the answer you'll often get is, not the same person, but also not different. Identity is like that. — Wayfarer

A tourist in Malaysia is trying to find the way back to his hotel. He sees a local monk and asks him in the little Malaysian he learned how to get there. The monk starts saying something about a rock and a bird. The tourist demands "How does that help me get back to my hotel?". The monk calmly shakes his head with a smile and walks away.

Call me Derek. — Tom Storm

Me three.

I believe most people would say it is still the same hammer. How is that so? We must find something that makes them the same. — Lionino

That is what universals set out to solve. That specific hammer is an instance of the tool of type 'hammer'. Hence the role of universals in predication - they are what allows something to retain an identity whilst still being an identifiable particular.

Therefore, even if time is discrete/discontinuous, should we believe that the person walking into time t+1 and the person walking out of it are the same? Is there really such a thing as spatio-temporal continuity in discrete time, and is it enough to account for identity? — Lionino

Where living beings are different to inanimate objects, is precisely that they maintain an identity whilst also changing. That has ramifications for biology but it becomes more acute in humans, who have a sense of self, a sense of what is right and wrong, and the ability to ponder their own identity. But I don't see any intuitive obstacle to considering the self from the perspective of process philosophy, as a kind of unified mind-stream, as it were. There are elements that change whilst others remain the same - again that's how identity operates, isn't it?

The monk calmly shakes his head with a smile and walks away. — Lionino

Perhaps sensing there's a communication problem that can't be overcome.

So specifically, I am searching for arguments, preferrably complete, even more preferrably in syllogistic form, for the belief that the self persists. Otherwise, I will remain in doubt, and in absence of any evidence of permanence, I will default to the position that it does not stay at all, and that we are constantly as always dying, as the comic posted in the first page depicts. — Lionino

What is relatively persistent, by comparison with with most cells of bodily organs, is neurons and the neural networks structures that supervene on them.

As a brain develops, young neurons strike out, seeking to form synaptic connections across brain regions, Harris said. If they fail to make those connections, they “commit suicide by consuming themselves.” And even if they survive this first cutthroat wave, they can “get pruned, like plants.”

In the first trimester of pregnancy, neural growth is exponential: about 15 to 20 million cells are born every hour, Harris said. Only about 50 percent of these original cells survive. If, for example, there are too many of one type, causing an imbalance, the excess will die off. Or, if some seem to be serving a pointless task, like those attending a shut eye, they’ll move on. Why waste precious neurons?

After the early period of growth, suicide, and pruning comes to an end, adult neurons survive for a lifetime. And unlike those of a cat, they remain malleable for several years. This is one reason kids are especially adept at learning new languages, and why procedures to correct neurological dysfunctions, like a lazy eye, have higher chances of success early in life.

https://news.harvard.edu/gazette/story/2022/05/a-tour-of-the-growing-brain-complete-with-upside-down-vision/

The issue of identifiying something as that which undergoes change is for me a very deep issue that involves, among other things, mereology and semantics.
Because of that, I summon Theseus' ship. I ask you: is it the same ship? — Lionino

In keeping with what a few others have mentioned:

Not that the Ship of Theseus has been satisfactorily resolved by anyone to date, but one way of looking at things in general is that any given’s identity is constituted of context-relative functionality. The ship remains the same ship in terms of context-relative functionality if the parts replaced relate to each other in such manner that the ship’s context-relative functionality is unchanged. I say “context-relative” because two different ships will hold the same functionality as ships, but their functionality will not be the same in terms of their immediate spatiotemporal contexts.

This, however, can get very abstract in the details of analysis.

All the same, as a thought experiment, I find that the sci-fi notion of teleportation operates on the same basis of identity just mentioned, this in fiction. Or, if a person were to lose a finger, for example, they would remain the same person X; but if a person were to so drastically change in terms of context-relative functionality, we will often state that they are not the same person they used to be, as is sometimes the case for extreme cases of dementia. Or else as can be the case when someone claims “he’s been a completely different person since he joined that click”.

This notion of identity seems to me particularly important to any version of a process philosophy wherein everything spatiotemporal, without exception, is in perpetual change. But then, in this interpretation, identity isn’t anchored to material particulars, being instead anchored to, again, a context-relative functionality.

With this perspective in mind, more directly addressing the OP, a person’s identity as a context-relative functionality can then be construed to persist subsequent to corporeal death, such as via reincarnations—granting both extreme outliers and continuity between these, such as in the same person’s life commencing with birth as an infant and possibly ending corporeal life with extreme changes in psyche. And, just as a river rock will be relatively permanent in comparison to the rushing waters that surround it, so too can one appraise that some core aspect of a psyche is relatively permanent in comparison to the percepts, etc., it experiences. This core aspect of psyche (which, for example, could conceivably persist from one lifetime to the next) can then be appraised as "that which undergoes changes". I however will emphasize: this does not then entail that there is such a thing as an absolutely permanent soul which thereby withstands any and all changes for all eternity.

This isn’t an argument I want to spend significant time in here defending. It would be quite a doozy. But it is the outline of a perspective that, notwithstanding the many details that would yet need to be ironed out, currently makes sense to me.

Stop pretending to know about a position you cannot even spell. — Lionino

Do you always resort to second rate abuse when you can't answer a question? :wink:

No pragmatist says "stop researching" to theoretical physicists and asks them to become engineers instead. — Lionino

Indeed, which is why I didn't say 'stop researching'. So well done there. I asked you why the question is important.

I asked what practical difference does it make to our quotidian life? What are the consequences/implications? I'd be interested in hearing your response. I ask the same question of idealism. What are the consequences of such metaphysical models for daily living?

I asked what practical difference does it make to our quotidian life? What are the consequences/implications? — Tom Storm

Aside from whatever the OP's response might be, I would think that, if one were to believe that there was indeed a judgement at the time of death, and that the fate of the soul depended on that, then it would make a difference to how you view your life, wouldn't it? I'm not saying I necessarily believe it, but I do fear that it might be true, and it does provoke existential angst. Whereas if one had the certain conviction that death was an absolute end, then this consideration wouldn't figure.

I would think that, if one were to believe that there was indeed a judgement at the time of death, and that the fate of the soul depended on that, then it would make a difference to how you view your life, wouldn't it — Wayfarer

Indeed. Well I attempted to address that above with -

And even if it does, my next question would be how does it matter in terms of how we live? How do we get from this to reincarnation or consequences for choices? Or some other cosmology and metaphysics which seeks to exploit this murky model? — Tom Storm

Which was my way of saying that it is one thing to think there is an eternal dimension to being and it's an another different thing to wrap a religious system around it. How do we arrive at a judgment model, with or without a deity?

I'm not saying I necessarily believe it, but I do fear that it might be true, and it does provoke existential angst. — Wayfarer

Yes, and that's one answer to the question that often informs these speculations. Fear.

my next question would be how does it matter in terms of how we live? — Tom Storm

Religions are often depicted in terms of 'carrot and stick' in our secular age, although I think it's a caricature. I understand the goal of Eastern religions, which is mokṣa or liberation, in terms of a transition to a wholly other dimension of being, one which is quite unimagineable from the naturalistic perspective and is therefore conveyed in mythological or symbolic form. It is plainly an extremely difficult thing to understand or see, and accordingly there is enormous scope for misunderstanding it, which accounts for a lot of the religious delusion that we see. Against that background, 'sin' is 'missing the mark' - failing to see some incredibly important point. That's what the various prophets, sages and seers are on about. The 'judgment model' that is implied by that is rather different to the historical narrative of Biblical tradition, as it is cyclical rather than linear, although the latter can be accomodated by the former rather more easily than vice versa. It revolves around not-seeing, or ignorance, a.k.a. avidya, which is the normal state of humanity - continuously failing to see the point of existence, so being repeatedly born into it (the meme behind the well-known film Groundhog Day).

a person’s identity as a context-relative functionality can then be construed to persist subsequent to corporeal death, such as via reincarnations—granting both extreme outliers and continuity between these, such as in the same person’s life commencing with birth as an infant and possibly ending corporeal life with extreme changes in psyche. And, just as a river rock will be relatively permanent in comparison to the rushing waters that surround it, so too can one appraise that some core aspect of a psyche is relatively permanent in comparison to the percepts, etc., it experiences. This core aspect of psyche (which, for example, could conceivably persist from one lifetime to the next) can then be appraised as "that which undergoes changes". I however will emphasize: this does not then entail that there is such a thing as an absolutely permanent soul which thereby withstands any and all changes for all eternity. — javra

:clap: That is conveyed in the rather poetic Buddhist term of the 'citta-santana', the mind-stream (nothing to do with the band, although, given Carlos' spiritual proclivities, something he probably regards as a happy accident.)

What impact does such a belief have for you, as someone with an interest in idealism and Buddhism? Surely there are versions of karma that would be understood in similar 'cause and effect' terms?

Didn’t I explain that already? :roll:

It didn't really come across. Do you mean this?

I'm not saying I necessarily believe it, but I do fear that it might be true, and it does provoke existential angst. — Wayfarer

I was thrown off when you then said this:

Religions are often depicted in terms of 'carrot and stick' in our secular age, although I think it's a caricature. I understand the goal of Eastern religions, which is mokṣa or liberation, in terms of a transition to a wholly other dimension of being, one which is quite unimagineable from the naturalistic perspective and is therefore conveyed in mythological or symbolic form — Wayfarer

Wasn't sure where this left things.

What I meant was, if there really is more to life than physical birth and death - if there were future consequences of actions taken in this life - then that would change the perspective on this life. I'm not saying you *should* believe it, but that if you did then it would change the perspective on what we do now. If you really believed that murder would result in hellish consequences in a future state then your own death may not appear as an escape into oblivion (as an extreme example).

I will add that, as far as Buddhist doctrine is concerned, the belief that at death the body returns to the elements, and there are no consequences of actions committed in life, is regarded as a form of nihilism. Although that said, I think trying to imagine what a next life would be or what that means, is obviously rife with possibilities for self-deception.

I think what you say is fair. I guess all I am proposing in response is that it's one thing to hold that birth and death are merely stages in eternity, but it is another thing entirely to have a system around this belief, to say that we know how it works and what we should do. (And I am not saying that you do) It's a bit like the idea of a deity. It's one thing to be open to the proposition. It is entirely a different thing to say you know what that deity wants.

I say “context-relative” because two different ships will hold the same functionality as ships, but their functionality will not be the same in terms of their immediate spatiotemporal contexts. — javra

So I guess that, beyond functionality (final cause in Aristotelian terms), spatiotemporal continuity is also important?

but if a person were to so drastically change in terms of context-relative functionality, we will often state that they are not the same person they used to be, as is sometimes the case for extreme cases of dementia — javra

Right.

I think that, for everything you said, it addresses a semantic and epistemological side of identity very well. That is, what it means when we call X, X. That is a side that most answers here chose when approaching the question.

One side that has not been exactly addressed so far is the phenomenological, subjective side. Besides any labels or linguistic aspects, are we now going to persist through time to the next second or is our consciousness going to finish and be replaced by another consciousness (someone else) with the appearance of being the same person as before due to memories? Are we gonna die in the next second, or is our conscious experience persisting across time?, is basically what is being asked. Now after thinking I wonder whether that question even makes sense, but maybe someone will bring it to light.

Also, I quite liked your art. The way you use gaps and separation on the canvas is something that I have never seen before.

The issue here is metaphysical, there is nothing in the physical world, I am quite confident, that will tell us "this is a person's essence". Neurons do not fulfill that task, for reasons such as neuroplasticity and the fact that their material composition does indeed change every time they undergo an electric pulse — like DNA, it does not change as much as our hair, but it does change. The reason why I made this thread is to address whether a metaphysical essence even exists, or whether the question even makes sense.

As best I can tell, the notion of "essences" doesn't refer to anything, and the use of the term often seems a matter of feigning knowledge where recognizing ignorance seems more warranted.

I'm not really interested in arguing the point though, and I just wanted to point out that there is relevant knowledge to be gained.

Carry on.

So I guess that, beyond functionality (final cause in Aristotelian terms), spatiotemporal continuity is also important? — Lionino

Aye. If one gets into the mindset outlined, and if, for example, here tersely outlined, one chooses to understand space as distance-between identities and time as a duration-between a) causes produced by identities and b) their effects/consequences—further deeming that space and time when thus understood are logically inseparable—then, spatiotemporal continuity is part and parcel of there being coexistent identities (in the plural). No coexistent identities—as is said of Moksha or of Nirvana without remainder or, in the West, of the notion of “the One”—then, and only then, one would derive there being no spacetime. Here isn’t an issue of which came first or of which is more important but, rather, that coexistent identities logically necessitate spacetime (when understood as just outlined, and not necessarily in a physicalist sense).

Are we gonna die in the next second, or is our conscious experience persisting across time?, is basically what is being asked. — Lionino

Addressing this via analogy to Theseus’s ship, if one for example replaces one plank on the ship, the ship itself continues through time unchanged (it currently seems to me uncontroversial to so stipulate). In parallel, if one as a conscious being experiences a new percept, one as the conscious being addressed will itself continue through time unchanged. My affinities are with process philosophy, so to me it is a continuation of ontic being as regards both the ship and one’s consciousness. This instead of identity consisting of individualized quanta-of-identity that are perpetually obliterated and (re)created over the course of time.

Did you have something else in mind other than the bifurcation of possibilities just specified?

Also, I quite liked your art. The way you use gaps and separation on the canvas is something that I have never seen before. — Lionino

Ah, this gave me a very good blush. Thanks for so saying.

That is conveyed in the rather poetic Buddhist term of the 'citta-santana', the mind-stream — Wayfarer

Thanks for the link. :up:

Others help to identify a continuity for me. A few years ago I signed deeds giving 'power of attorney' to two old friends if I become unable to look after my own affairs. To sign such a deed says, I imagine a future where someone - identified by others whom I love as me - needs care. I am old enough to know people of my sort who have lost their sense of who they are, so I recognise the future me might regard these 'two old friends' when they eventually interfere in my life as mysterious kind, or indeed unkind, strangers. All the same, I trust them, here and now and pledged for the future, provided of course they're still compos mentis themselves, to know 'who I am'.

Socio-politically, the problem of personal identity hit a crisis around 1900. Before then you could travel across a hill, or ocean, and just become someone else - unless you were unlucky enough to meet someone from a past life in your new present one.

But around 1900 states began to want to identify 'persistent criminals' and 'immigrants' as having a certain set of characteristics. Passports slowly became more common. Fingerprints emerged as a scientifically dodgy solution, although the Bertillon system in France was much more reliable.

Just, broadly, to emphasise: the problem of continuity of identity is often one for others: I am not the same as I used to be. But 'others' can in this context include versions of oneself at other times. I, in the present, still hold 'myself' responsible responsible for a reprehensible thing 'I' did in 1978: but it cannot be made good by the present I, only acknowledged and, perhaps, entered as a debit on a ledger where moral credits are also claimed.

I, in the present, still hold 'myself' responsible responsible for a reprehensible thing 'I' did in 1978: but it cannot be made good by the present I, only acknowledged and, perhaps, entered as a debit on a ledger where moral credits are also claimed. — mcdoodle

Speaking in generalized terms, the same applies here. As to regret, in keeping with some of Nietzsche’s writings as I best interpret them, regret that causes dysfunction, any form of paralysis of being, is unhealthy and should be done away with. Having said that, regret still serves an important purpose in the here and now—even if full atonement for the past deed(s) cannot be obtained—in that it plays a rather crucial role in one’s not repeating past mistakes/wrongs in the present and in the future. If there is no regret for X, one will again willfully do X whenever conditions allow. With regret, however, one is often left with (re)paying things forward, so to speak. Although I don’t mean to be preaching to the choir here. But yes, regret is one aspect of psychological being that directly points to the continuation of one’s psyche over time. :up:

We are constantly changing, all the cells that constitute our bodies replaced every seven or so years according to some accounts. On the other hand, are we not distinguishable as the entities that undergo those changes? — Janus

This is another example that shows we intuitively know we are not our bodies. Believing that we are an amalgamation of matter is like pounding a square peg in a round hole: it results in the mind-body problem and impossible-to-resolve paradoxes. It's so much more parsimonious to conclude the physical realm doesn't exist.

This is another example that shows we intuitively know we are not our bodies. — RogueAI

It doesn't show me that. I also don't see parsimony in the belief that the physical realm doesn't exist; instead, I see that as contravening Peirce's maxim: "Let us not pretend to doubt in philosophy what we do not doubt in our hearts".

I’d cite the abundance of veridical near death experiences as evidence of the soul and an afterlife.

One side that has not been exactly addressed so far is the phenomenological, subjective side. Besides any labels or linguistic aspects, are we now going to persist through time to the next second or is our consciousness going to finish and be replaced by another consciousness (someone else) with the appearance of being the same person as before due to memories? Are we gonna die in the next second, or is our conscious experience persisting across time?, is basically what is being asked. Now after thinking I wonder whether that question even makes sense, but maybe someone will bring it to light. — Lionino

Again I'll refer to Buddhist philosophy here, as it is one that I have some familiarity with, and secondly, because of the Buddhist principle of anatta or anatma (usually given as no-self) grappled with this question over many centuries.

It is generally understood, and often stridently argued, that 'the Buddha says there is no self or abiding soul'. But this is not quite as it seems. On closer analysis, what the Buddhists argue against is the idea of a permanent self in the sense of being something utterly impervious to change, the same always and everywhere. A couple of canonical examples of the view in question:

The self and the world are eternal, barren, steadfast as a mountain peak, set firmly as a post. And though these beings rush around, circulate, pass away and re-arise, but this remains eternally.

‘This is the self, this is the world; after death I shall be permanent, everlasting, not subject to change; I shall endure as long as eternity’ - this too he regards thus: ‘This is mine, this I am, this is my self'

These are the views characteristic of what the Buddha describes as 'eternalism', in the context of a culture where there was some belief in repeated births, and against the view that the aim of religious discipline is to secure fortuitous rebirths in perpetuity. The aim of the Buddhist teaching is not to secure fortuitous rebirth, but to escape the cycle of birth and death.

But, against all of this, when the Buddha is asked straight out whether the self exists, he declines to answer, on the grounds that it is not a yes/no question. To answer 'yes' is to side with the 'eternalists' (like those above) whilst to answer 'no' would only confuse the questioner. It turns out that the statement 'nothing is self' is not quite the same as 'there is no self'.

There's a very early text called the Questions of King Milinda, in which a Buddhist monk, Ven. Nagasena, illustrates the principle of anatta in dialogue with a Greco-Bactrian king, King Milinda (thought to be an historical figure, Menander). In it, Nagasena asks the King how he came to their meeting.

"I did not come, Sir, on foot, but on a chariot."

"If you have come on a chariot, then please explain to me what a chariot is. Is the pole the chariot?"

"No, Reverend Sir!"

"Is then the axle the chariot?"

"No, Reverend Sir!"

"Is it then the wheels, or the framework, of the flag-staff, or the yoke, or the reins, or the goad-stick?"

"No, Reverend Sir!"

"Then is it the combination of poke, axle, wheels, framework, flag-staff, yoke, reins, and goad which is the "chariot"?"

"No, Reverend Sir!"

"Then, is this "chariot" outside the combination of poke, axle, wheels, framework, flag-staff, yoke, reins and goad?"

"No, Reverend Sir!"

"Then, ask as I may, I can discover no chariot at all. This "chariot" is just a mere sound. But what is the real chariot? Your Majesty has told a lie, has spoken a falsehood! There is really no chariot!" — Milindapanha

However, I, for one, find that analysis quite unsatisfactory, because what the King possessess over and above any particular chariot, is the idea of a chariot, which, in that day and age, might have meant the difference between having an empire and not having one, as the chariot was an enormously consequential invention. (Put that down to my Platonist cultural heritage).

In any case, the Buddhist tradition itself began to realise some difficulties with this view. Ultimately this gives rise to the later Mahāyānist teaching of the ālaya-vijñāna, 'the eighth consciousness, being the substratum or ‘storehouse’ consciousness according to the philosophy of the Yogācāra. The ālaya-vijñāna acts as the receptacle in which the impressions (known as vāsanā or bīja) of past experiences and karmic actions are stored. From it the remaining seven consciousnesses arise and produce all present and future modes of experience in saṃsāra, as well as maintaining one's sense of personal continuity (the citta-santana). At the moment of enlightenment (bodhi), the ālaya-vijñāna is transformed into the Mirror-like Awareness or Prajñāpāramitā of a Buddha.'

Comparisons have been made between the Buddhist ālaya-vijñāna and C G Jung's 'collective unconscious'. According to Jung, this collective unconscious is the source of archetypes – universal, archaic symbols and images that derive from the shared experiences of our ancestors. These archetypes manifest in our dreams, mythologies, and religious beliefs.

The comparison between these two concepts often revolves around the idea that both represent a deep, underlying level of consciousness that is not directly accessible to our everyday conscious mind but manifest through our perceptions, thoughts, and behaviors. Both suggest a repository of latent, accumulated experiences – in the case of ālaya-vijñāna, these are individual and karmic, while for the collective unconscious, they are universal and archetypal.

If all the cells in our bodies, in organisms generally, contain a unique DNA sequence that defines them then that is different than the 'ship of Theseus'. It is also a matter of metabolism. Look up 'self-organization' and you will see why it does not apply to ships or to anything other than organisms..

Well you're right that personal identity of say, humans is fundamentally different from the 'ship of Theseus'. But the difference isn't because of DNA, it's because citizens exist both objectively (our bodies) and inter-subjectively (our identities), whereas archeological finds, such as ships, only exist objectively.

The turnover of cells (and thus molecules) of a human's body change our objective existance. However most layperson conversations about who we are do not use objective existance as the defining criteria. Commonly we use our inter-subjective existance (that is our existance as agreed upon by say, our community) as what we mean in conversation. Thus I am: my name, my family position, my profession, my reputation, my history. To myself, I am my memories and my beliefs and outlook. None of these is primarily defined by cells nor molecules.

OTOH a physical ship can slowly devolve from being 97% intact (or authentic) through lower and lower numbers until it hits zero and becomes a reproduction and no longer the ship of Theseus.

I agree with what you say about the intersubjective conventional notions of identity, subjectivity and objectivity. I was only pointing out that cell replacement is an internally driven and regulated activity and most of the cells of a biological body contain DNA unique to that particular organism; so this fact can be a criterion for determining unique identities, biologically speaking.

Returning to Descartes' Metaphysical Meditation #3 which the OP started with. I have come to the view that it contains an egregious equivocation which is at the heart of many profound problems associated with the 'post-Cartesian' outlook.

He says:

"when I think that a stone is a substance, or a thing capable of existing of itself, and that I am likewise a substance, although I conceive that I am a thinking and non-extended thing, and that the stone, on the contrary, is extended and unconscious, there being thus the greatest diversity between the two concepts, yet these two ideas seem to have this in common that they both represent substances".

Descartes' dualism posits two fundamentally different kinds of substances: the thinking substance (res cogitans) and the extended substance (res extensa). In Descartes' view, the mind (a thinking, non-extended thing) and the body (an extended, non-thinking thing) are distinct types of substances. He emphasizes the ability of these substances to exist independently, which is central to his dualistic framework. But at the same time, he says they both 'have this in common, that they both represent substances'.

It seems to me that here is where there is a major divergence between Descartes' and Aristotelean 'hylomorphic dualism' (as understood in Scholastic philosophy.) I think Descartes concept of 'Substance' in particular is very different, in taking 'a stone' as 'a thing capable of existing of itself'. I would have thought that hylomorphic dualism would not recognise a 'stone' as being a 'substance' in the sense they understand the term, namely, as a composite of matter (hyle) and form (morphe). I wonder if much thought was even given to such things as stones in their philosophy? I would have thought hylomorphic dualism was more concerned with the organic realm than with mineral substances.

Anyway, it is here that Descartes (1) equivocates the meanings of substance (ouisia in the Aristotelean terminology) with the everyday sense of the term (a material with uniform properties), and (2) posts 'res cogitans' as a 'substance' in an objective sense, that is something that exists objectively as a real thing ('res' meaning 'thing'.) I think the case can be made that this is where many of the deep confusions about mind and body that continue to bedevil western philosophy originate.

Good point, hence Kant’s attribution of “problematic” idealism to Descartes on the one hand, and his specificity of substance as a pure category on the other.

Yes re-reading Descartes again after a long time, I can see the cogency of Kant’s critique.