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Does Kant's philosophy of perception and intuition imply that the unity of perceived individuals is an intuition? If so, this seems to resolve the various paradoxes of physical individuals such as the problem of change over time and the ship of Theseus (after you gradually replace every part in the original ship, is it still the same ship?).

If our view of the universe as a collection of individuals is a part of the possibility of perception rather than a noumenal fact of the universe, those problems seem to vanish, but I don't recall ever seeing this rather dramatic point ever being discussed in relation to Kant.

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  • I guess it isn't written much about because all it does is shifting the problem from the identity of one object (substance) to the identity of another subject (representation)?
    – Philip Klöcking
    Apr 4, 2023 at 19:59
  • @PhilipKlöcking, but the identity of a physical object has to be understood in terms of physical properties; the identity of an intuition only has to be understood as a feature that makes the world accessible. It doesn't have to avoid paradoxes. Apr 4, 2023 at 20:03
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    The ship as physical object does not disappear in Kant, it's metaphysical nature just shifts from substance to representation. The paradox of the Ship of Theseus is about how it can remain the same object of cognition while being replaced part by part, ie. about the identity of an object of cognition. You apply a physicalist ontology to Kant here and the compatibility is questionable
    – Philip Klöcking
    Apr 4, 2023 at 20:08

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The resolution to the paradox is that humans categorise the stuff of the world in subsets that have a useful and intuitive meaning. The ship of Theseus is ultimately a vast collection of fundamental particles, most of them identical to the fundamental particles that comprise the air around the ship and the water under the ship. We distinguish the subset we think of as the ship for a number of reasons- it has a distinctive shape, it is owned by Theseus, it is used by Theseus to complete voyages, and so on. If we replace parts of it, or even if over time we replace every plank of it, we are still left with a collection of fundamental particles that is owned by Theseus, used by Theseus to complete voyages and has a certain shape. For all purposes that are important to humans on an everyday basis, it is still the ship of Theseus. The same principle applies to countless other objects. I think of myself as me notwithstanding the fact that my body today probably contains only a small fraction of the fundamental particles that comprised me fifty years ago- that is because the important things about 'me', namely my overall shape, my thoughts and memories, are unaffected by the ongoing rate at which the cells in my body dies off, are excreted and replaced with matter I have ingested or breathed in.

So, yes, your perception of the unity of individuals is just that- a useful and intuitive labelling of subsets of matter based on factors that are meaningful to you.

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Kant says, in the First Analogy of Experience, that we perceive objects enduring in time, i.e. substances, with only their states changing. He furthermore states that there is a connection of this principle to the law of conservation of matter of physics of his time and that this principle is due to the necessity of representing the unity of time by the subject in the object, as far as its an object of experience, and thus formed according to space and time (per Transcendental Aesthetic). Kant says that we represent the unity of time in the object of experience by representing it as an enduring substance with changing states.

We, however, need, as you note, a criterion for the identity of these substances. Since all states of a substances, in principle, might change, it's not trivial to determine whether two subsequently perceived, materially (in the sense discussed by Kant's Postulates of Empirical Thought) different objects constitute the same substance (in which case we perceive change) or are different (in which we merely perceive two distinct object one after the other). Kant makes this distinction as the distinction between representation of sequence [in time] and sequence of representations [in time].

Kant investigates the conditions of empirically perceiving (as Sebastian Rödl notes, in his Categories of the Temporal, page 185-186, many commentators think that Kant denies our ability to perceive change which is refuted by him in the plainest words) change, or, in other words, perceiving that some substance was some way and now isn't that way. For example, the Ship of Theseus being repaired constitutes a change. He posits that in any perception of change we find an application of a general rule according to the category of causality. We, however, have no certain knowledge about causal laws (thus the relational categories, like causality, are dynamical and their corresponding principles, i.e. the Analogies of Experience, are regulative). This is then also true of the determination of the identity of substances inbetween perceptions - we might be wrong about that, although ultimate, exhaustive natural science would provide sufficient knowledge for determining their identity in time.

There's also, as I said, a connection to Kant's discussion of Newtonian physics in Metaphysical Foundations of Natural Science, but it's somewhat unrelated to your question, so I can just reccommend you to read the work, if you're interested.

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  • Remember that Kant bases his views on an outdated model of physics, though. His derivations aren't wrong, but the premises are. Mar 21 at 6:18
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From WP on transcendental idealism:

Kant means that his philosophical approach to knowledge transcends mere consideration of sensory evidence and requires an understanding of the mind's innate modes of processing that sensory evidence... In the "Transcendental Aesthetic" section of the Critique of Pure Reason, Kant outlines how space and time are pure forms of human intuition contributed by our own faculty of sensibility. Space and time do not have an existence "outside" of us, but are the "subjective" forms of our sensibility and hence the necessary a priori conditions under which the objects we encounter in our experience can appear to us at all. Kant describes time and space as "empirically real" but transcendentally ideal.

Thus, while we apprehend the Ship of Theseus by "empirically real" physical characteristics, it's size, color, weight, etc., the ship exists not merely as a physically real vessel, but a "transcendentally ideal" vessel, and the difference between the transcendentally ideal is not one of mere appearance and actuality. What is actual is noumenon, and cannot be known since knowing entails escaping phenomenon, which is a construction of the mind.

The ship as physical object does not disappear in Kant, it's metaphysical nature just shifts from substance to representation. The paradox of the Ship of Theseus is about how it can remain the same object of cognition while being replaced part by part, ie. about the identity of an object of cognition. You apply a physicalist ontology to Kant here and the compatibility is questionable. – Philip Klöcking

It is certainly questionable for a Continental thinker such as most learned and formally trained sysadmin (and whose knowledge of Kant is far superior to many here) to look for a physically reductionist grounding of Kantian notions, but it is actively a part of the Oxfordian Nicholas Shea's research in his book Representation in Cognitive Science. In such a metaphysical framework of thinking, one might suggest humbly that transcendental idealism does anticipate certain findings such as those which show that perception provides consciousness a construction as per the research programme of visual computation. Thus, what metaphysically presents itself as the Ship of Theseus problem of identity, might be suggested to unravel into a constructivist epistemology in so far as our intuitive notions of the existence of things isn't a denial of the substance involved in identity, that is the objective form of matter and the existence that can be broadly construed as a noumenological ship, but rather furthering Kant's motivations of characterizing identity and categorization within a program of accepting neural computation and conceptual metaphor as building blocks of thoughts in contradistinction to more classical philosophical notions in the philosophy of mind such as the language of thought (SEP). In this way, one rejects the contemporary arguments to re-embrace direct realism such as Searle argues, and at the same time, dispense with the notion that human thought is primarily linguist and rational, but instead is seated in what Searle himself calls "The Background", that nebulous state of affairs most philosophers are happy to call intuition.

Does Kant's philosophy of perception and intuition imply that the unity of perceived individuals is an intuition? If so, this seems to resolve the various paradoxes of physical individuals such as the problem of change over time and the ship of Theseus

On my reading, yes. Kant was attempting to show in transcendental idealism and with his phenomenological and noumenological distinction that subjectivity and objectivity and the mental and the physical are cross-cutting concerns, to use contemporary CS-AOP terminology. Your intuition that Kant anticipates dissolving the paradox inherent in the Ship of Theseus is an accurate one if you accept that conceptualization is a process of the mind that is anchored in linguistic faculty and not some Platonic intuition of a transcendental reality in which concepts exist as real forms. That is to say, that an anti-realist approach to categorization can be seen as a natural outcome of Kantian thinking. This too seems to affirm late LW in PI where he posits family resemblance, an idea taken up and furthered by Eleanor Rosch and eventually George Lakoff starting with prototype theory to understand the linguistic basis of concept and the nature of apriorticity.

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  • You once objected to a suggestion that concepts as an experience are rooted in language by stating "Concepts have nothing to do with words". I would ask you to reconsider that concepts are categories rooted in linguitistic and normative intuition whose appearance of mind-independent objectivity are actually from the commonality of the physical neurons that can be seen as underpinning and thus normatizing neural computation.
    – J D
    Apr 7, 2023 at 16:16
  • But that's just me in my uncharacteristically IMHO-approach to persuade you to consider continuing to apply a physical ontology to representation following your analytic intuition in contradistinction to our learned Herr Klöcking whose Kantian knowledge extends to a reading in the language of the author within the context of an expertise German in German philosophy.
    – J D
    Apr 7, 2023 at 16:20
  • First off, if going that route, I'd suggest taking a Sellarsian approach. Secondly, Kant is nothing like a platonist and calling the noumenal the actual is pretty contra Kant ins some ways. Thirdly, I think even the extensive SEP entry is missing the most obvious reading: There is both an epistemic and metaphysical dual-aspect of phenomenal and noumenal. Even claiming either that a noumenal object is spatial or it's non-spatial is so ignorant of central ideas of Kant that I am sure I got more grey hair now.
    – Philip Klöcking
    Apr 7, 2023 at 21:27
  • The problem here is that people like to make black-and-white categories: there is appearance and thing-in-itself both epistemically and ontologically as aspects. But while there is "things of the objects we can know under the metaphysical epistemic conditions we have" there is also "things of the objects we can know under the empirical epistemic conditions we have". Therefore, there are properties we know about the objects, properties we could, in principle, know but do not yet know, and properties we cannot know. And we just cannot know whether noumena are spatio-temporal.
    – Philip Klöcking
    Apr 7, 2023 at 21:46
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    Let us continue this discussion in chat.
    – J D
    Apr 8, 2023 at 15:23

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