Anyone care to read Kant's "Critique of Pure Reason"? “…. Reality (…) is that which corresponds to a sensation in general; that, consequently, the conception of which indicates a being (in time)….”
To establish the reality of space empirically, such that it may be an empirical reality, is to establish that space corresponds to a sensation. And, accordingly, each space its own sensation.
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“…. The effect of an object upon the faculty of representation, so far as we are affected by the said object, is sensation….”
It follows that space, if it is an empirical reality and corresponds to a sensation, is an effect upon the faculty of representation insofar as we are affected by it, hence, is the effect of an object, from which follows necessarily that space is an object.
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“… In whatsoever mode, or by whatsoever means, our knowledge may relate to objects, it is at least quite clear that the only manner in which it immediately relates to them is by means of an intuition. (…)
“….That sort of intuition which relates to an object by means of sensation is called an empirical intuition. (…)
Space, insofar as it is an empirical reality corresponding to a sensation, and insofar as space relates to an object via its sensation, is space therefore an empirical intuition.
“….The undetermined object of an empirical intuition is called phenomenon. That which in the phenomenon corresponds to the sensation, I term its matter….”
Space, as an undetermined object of an empirical intuition, has that which corresponds to its sensation, and is its matter.
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“….Those who maintain the empirical reality of time and space, whether as essentially subsisting, or only inhering, as modifications, in things, must find themselves at utter variance with the principles of experience itself. For (…) they must admit two self-subsisting nonentities, infinite and eternal, which exist (yet without there being anything real) for the purpose of containing in themselves everything that is real.…”
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“…. Our expositions, consequently, teach the reality (i.e., the objective validity) of space in regard of all which can be presented to us externally as object, and at the same time also the ideality of space in regard to objects when they are considered by means of reason as things in themselves, that is, without reference to the constitution of our sensibility.…”
The expositions teach, from the perspective of 1780’s physics, but transcendental philosophy proves the expositions are wrong. In other words, Kant’s expositions merely reiterate the SOP of the day, given Newtonian conditions, which just is to profess that our knowledge is of things as they are in themselves. To remove the absurdities of operating with infinities, it must be shown space and time do not belong to things of which our knowledge consists. To show space and time do not belong to those things, it must be shown that it is not things as they are in themselves of which our knowledge consists. It follows that if it is not things in themselves we know, it is not necessary for that of which we do know, to have space and time attributed as belonging to them, even if it remains necessary for some account of them in relation to that of which our knowledge does consist.
If Kant were to think space and time inhere or subsist in themselves, and thereby they represent empirical reality, hence can be properties of things, he contradicts the tenets of his own epistemological metaphysics, not to mention it beggars the imagination as to why he would spend ten years constructing a philosophy in which it is proved they don’t, for the excruciatingly simple reason everything we know of empirical content, without exception….is in fact in reference to the constitution of our sensibility.