, altering the physical state of the brain would automatically alter what that brain comprehends. — RussellA

Yeah for sure it boils down to this. I think there are certainly novel ways of thinking not available to that everyday normal consciousness. I think we’ve been robbed of decades of potentially very fruitful work with altered states by the drug war and social mores. Tsk tsk. That said, it’s clearly a tool and guarding against overzealousness in many forms is important. You are after all, out of your mind

@Corvus @Wayfarer

The term "Transcendental Idealism" is central to the Critique of Pure Reason
In the Conceptual Map of the Critique of Pure Reason, the first item is Transcendental Idealism, establishing the importance of the term.

Kant defines "Transcendental Idealism" in the Fourth Paralogism"
A 369 I understand by the transcendental idealism of all appearances the doctrine that they are all together to be regarded as mere representations and not as things in themselves, and accordingly that space and time are only sensible forms of our intuition, but not determinations given for themselves or conditions of objects as things in themselves.

In today's terms, Indirect Realism, aka Representative Realism.

Kant did propose that the term could be improved
However, Kant did propose that the phrase "Transcendental Idealism" could be improved.
In the Introduction to the CPR:
Specifically, he differentiated his position from Berkeleian idealism by arguing that he denied the real existence of space and time and the spatio-temporal properties of objects, but not the real existence of objects themselves distinct from our representations, and for this reason he proposed renaming his transcendental idealism with the more informative name of "formal" or "critical idealism," making it clear that his idealism concerned the form but not the existence of external objects.

Therefore, the term Transcendental Idealism should be treated more as a figure of speech than literally.

It is a transcendental idealism not a transcendent idealism
Note that it is Transcendental Idealism not Transcendent Idealism, meaning that it is about the limits of what we can cognize about our experiences having been determined a priori before having such experiences. It is not about being able to cognize about our experiences beyond limits predetermined a priori .

Kant is putting a limit on our cognitive abilities.

A priori pure intuition of space and time and a priori pure concepts of the understanding (the Categories)
Space and time are the Categories are both a priori, however, space and time is the necessary foundation for the categories. For example, we have the concept of space and we have the concept of a number such as two, though it is a fact that although we can imagine empty space empty of numbers, we cannot imagine numbers outside of space. Consequently, first is the pure intuition of space and time within which are the pure concepts of the understanding (the categories).

We can use our cognitive facilities on our sensibilities about external objects affecting our sensibilities, but what we are able to cognize is limited by our a priori pure intuition of space and time and the a priori pure concepts of the understanding (the Categories).

What for Kant is the source of the a priori?
Kant says we have no innate knowledge of any particular proposition, ie, "postboxes are red", but he does say that it is not the case that our sensibilities are the cause of what we cognize about them but rather an priori cognitive ability makes sense of these sensibilities, ie, I perceive the colour red rather than the colour green when looking at a wavelength of 700nm

Introduction: Kant agrees with Locke that we have no innate knowledge, that is, no knowledge of any particular propositions implanted in us by God or nature prior to the commencement of our individual experience. But experience is the product both of external objects affecting our sensibility and of the operation of our cognitive faculties in response to this effect (A I, B I), and Kant's claim is that we can have "pure" or a priori cognition of the contributions to experience made by the operation of these faculties themselves, rather than of the effect of external objects on us in experience.

IE, Kant's position is that of Chomsky's Innatism rather than Skinner's Behaviourism.

Understanding Transcendental Idealism using the analogy of colour
When a wavelength of 700nm enters my eye, I see the colour red because I have the innate ability to see the colour red when looking at a wavelength of 700nm. When a wavelength of 300nm enters my eye, I don't see the colour ultra-violet, because I don't have the innate ability to see the colour ultra-violet when looking at a wavelength of 300nm.

This is the meaning of transcendental in "Transcendental Idealism", in that the colours I can see when looking at different wavelengths has been limited by a priori conditions of perception. and has the consequence that because I can see a colour such as red, this doesn't of necessity mean that the colour red exists in the world.

The fact that I cannot see the colour ultra-violet when looking at a wavelength of 300nm is why the term isn't "transcendent idealism".

"Idealism" because the colour red exists in my mind not the world.

Kant is a Realist because, for him, the cause of our seeing the colour red originated outside our mind rather than within our mind.

The relationship between objects and their properties
Kant does not directly deal with objects of empirical cognition, but investigates the conditions of the possibility of our experience of them by examining the mental capacities that are required for us to have any cognition of objects at all. (Introduction page 6)

As regards properties, suppose I see a red postbox. The postbox is an object and redness is a property. But what are objects? An object is no more than a set of properties, in that if all the properties of an object were removed, no object would remain, in that is it impossible to imagine an object if it has no properties.

So a postbox is the set of properties such as redness, rectangular, extended in space, etc, but as the property redness only exists in the mind of the perceiver and not the world, one can conclude that the object, which is no more than a set of properties, where properties exist in the mind of the perceiver and not the world, also only exists in the mind of the perceiver and not the world.

Therefore, not only do properties such as redness only exist in the mind, but also objects such as postboxes only exist in the mind as concepts.

Interpreting A369
I understand by transcendental idealism that all appearances of objects such as postboxes and properties such as redness are to be regarded as mere representations and not as things in themselves, ie, postboxes and the colour red existing in the world, and accordingly, what we perceive as space and time only exists in the mind as a foundation for being able to perceive objects and their properties as mere representations and not as things-in-themselves.

The space, time, objects and properties we perceive only exist in the mind, although we can reason about their existence in the world using the transcendental category of causation.

Balboa Park, San Diego, 1971, windowpane. — Mww

Sounds like a nice place. Never been there, so afraid it is a place of imagination for me.

You know, laying in the grass, you can’t tell the difference between imagining the grass is growing or your head is shrinking? — Mww

If you are an idealist, then none of your claims can be refuted suppose. :D

Space and time are the Categories are both a priori, however, space and time is the necessary foundation for the categories. For example, we have the concept of space and we have the concept of a number such as two, though it is a fact that although we can imagine empty space empty of numbers, we cannot imagine numbers outside of space. Consequently, first is the pure intuition of space and time within which are the pure concepts of the understanding (the categories).

We can use our cognitive facilities on our sensibilities about external objects affecting our sensibilities, but what we are able to cognize is limited by our a priori pure intuition of space and time and the a priori pure concepts of the understanding (the Categories). — RussellA

Kant is a Realist because, for him, the cause of our seeing the colour red originated outside our mind rather than within our mind. — RussellA

I am not sure if anyone claims that space is internal intuition or categories, then whether he could be qualified as a realist. Shouldn't he be an idealist?

I am not sure if anyone claims that space is internal intuition — Corvus

Apart from Kant:

A23: Space is not an empirical concept that has been drawn from outer experiences. For in order for certain sensations to be related to something outside me (i.e., to something in another place in space from that in which I find myself), thus in order for me to represent them as outside one another, thus not merely as different but as in different places, the representation of space must already be their ground) Thus the representation of space cannot be obtained from the relations of outer appearance through experience, but this outer experience is itself first possible only through this representation.

A25: Space is not a discursive or, as is said, general concept of relations of things in general, but a pure intuition.

From SEP article on Kant's Views on Time and Space

The distinction between sensation and intuition in Kant’s thinking is fundamental to his overarching conception of space and time. This is the case for several reasons, not least because one should avoid thinking that Kant takes us to have a sensation of space; we have, rather, an intuition of it (see Carson 1997).

This idea comprises a central piece of Kant’s views on space and time, for he famously contends that space and time are nothing but forms of intuition, a view connected to the claim in the Transcendental Aesthetic that we have pure intuitions of space and of time.

From SEP article on Kant's Views on Time and Space — RussellA

I try not to 100% rely on or accept the internet sites information even SEP (because even SEP they don't have various different commentaries on the same topic - they tend to have 1 commentary or article on 1 topic - entails possible biased view). I try to read the original works and various printed commentaries.

If you claim that Space and Time was solely pure intuitions and concepts in Kant, and has nothing to do with the physical entity in the external world, then should you not brand Kant as an idealist, rather than Representative Realist?

It looks a contradiction to accept the view Kant's concept of Space and Time was solely internal intuition or concept, and then at the same time claiming that he was a some sort of Realist.

This idea comprises a central piece of Kant’s views on space and time, for he famously contends that space and time are nothing but forms of intuition, a view connected to the claim in the Transcendental Aesthetic that we have pure intuitions of space and of time. — RussellA

Kant mentions dichotomy of the types of knowledge, experience and the world in CPR i.e. a priori / a posteriori, analytic / synthetic, phenomenon / noumenon, transcendental idealism / transcendental realism, ... therefore why not space and time as pure intuition / space and time as empirical reality? CPR has many suggestive writings on the dichotomies. I am not sure why most of the traditional Kant commentators have been seeing only the one side of the story.

It is vital to bear in mind that I am not denying Kant said that space and time was a priori pure intuition in CPR. He did. But he also had in mind that space and time is empirical reality out there too, although he doesn't make big song and dance about it. We need to consider why Kant had to do that in the full schema of his plans, ambitions and duties in CPR. There must be reasons for him having done what he did.

I try not to 100% rely on or accept the internet sites information — Corvus

I agree.
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If you claim that Space and Time was solely pure intuitions and concepts in Kant, and has nothing to do with the physical entity in the external world, then should you not brand Kant as an idealist, rather than Representative Realist? — Corvus

Kant is an idealist in the same sense that an Indirect Realist is an idealist, in that what is perceived is only a representation of something existing outside the mind. IE, because we perceive a bent stick does not mean that the stick is actually bent in the world.

Kant is a realist in the same sense that an Indirect Realist is a realist, in that the representation of something in the mind has been caused by something outside the mind. IE, there is actually something in the world causing our perception of a bent stick.

If, however, Idealism was defined as the belief that there is nothing outside the mind and Realism was defined as the belief that there is something outside the mind, then in that case one could only be a believer in either Idealism or Realism. Under this definition, Kant would be a believer in Realism.
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It is vital to bear in mind that I am not denying Kant said that space and time was a priori pure intuition in CPR. He did. But he also had in mind that space and time is empirical reality out there too, although he doesn't make big song and dance about it. — Corvus

I agree that Kant as a believer in Realism would have agreed that there is a world outside the mind that exists independently of the mind. Within this world there is something that can be called space and time that is the cause for the perception of space and time in our minds.

However, the space and time we perceive in our mind is not of necessity the same as the space and time existing in a mind-independent world that is causing our perception. For example, when looking at a wavelength of 700nm we may perceive the colour red. It is true that the wavelength of 700nm caused our perception of the colour red, but it cannot be argued that a wavelength of 700mnm and our perception of the colour red are in any way similar.

"Space" and "time" can refer to what we perceive in the mind and can also refer to the cause of our perception existing in a world outside the mind. We know our perception of space and time in the mind, but the space and time in a mind-independent world are just names for unknown things.

IE "space" and "time" as pure intuition refer to known perceptions in the mind, whilst "space" and "time" as empirical reality refer to unknown things existing in a mind-independent world causing our known perceptions.

I agree. — RussellA

:up:

IE "space" and "time" as pure intuition refer to known perceptions in the mind, whilst "space" and "time" as empirical reality refer to unknown things existing in a mind-independent world causing our known perceptions. — RussellA

So your view is also for Kant's space and time as both empirical reality and pure intuitions too. :up:
Any idea why he had to go that way in CPR?

So your view is also for Kant's space and time as both empirical reality and pure intuitions too — Corvus

Yes, for Kant, space and time are empirically real, and space and time are pure forms of all intuitions.

Introduction to CPR - Kant's thesis that space and time are pure forms of intuition leads him to the paradoxical conclusion that although space and time are empirically real, they are transcendentally ideal, and so are the objects given in them.

Introduction to CPR - Kant argues that space and time are both the pure forms of all intuitions, or ''formal principle(s) of the sensible world," and themselves pure intuitions. They are the forms in which particular objects are presented to us by the senses, but also themselves unique particulars of which we can have a priori knowledge, the basis of our a priori knowledge of both mathematics and physics. But the embrace of space and time "is limited to actual things, insofar as they are thought capable of falling under the senses" - we have no ground for asserting that space and time characterize things that we are incapable of sensing.

However, this does not mean that we know the reality of space and time in the world, as we can only know them transcendentally.

As an analogy, if I am within a closed room and hear a knocking of the outer wall, I know that there is something outside the room even if I don't know what it is from the principle that every effect has a cause. The fact that I know there is something does not mean that I know what it is.

As an another analogy, although when perceiving the colour red, I know something caused my perception, I don't know of necessity what that something was.

As an another analogy, I know something that exists wrote "So your view is also for Kant's space and time as both empirical reality and pure intuitions too", but I don't know what that something is.

Similarly, Kant knows that space and time are empirically real in the world from the Principle of Sufficient Reason, but has no knowledge as to what they really are.

Any idea why he had to go that way in CPR? — Corvus

In order to establish what is named today, as I understand it, as Indirect Realism, still not accepted by the Direct Realists after 200 years of debate, including people such as Hilary Putnam and John Searle.

“…. 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.
———-

“…. 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.
———-

“… 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.
—————-

“….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.…”
—————-
—————-

“…. 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.

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, on the one hand contradict itself, and on the other spent ten years constructing a philosophy in which it is proved they don’t. — Mww

I'm still interested in Critique of Pure Reason.

For Kant, as an Empirical Realist, space and time and the matter within it are empirically real. However, this can only be established by synthetic a priori judgements, empirically through the sensible intuitions of phenomena and appearance and transcendentally through the non-sensible intuitions and understanding.

Introduction to CPR - Kant's thesis that space and time are pure forms of intuition leads him to the paradoxical conclusion that although space and time are empirically real, they are transcendentally ideal, and so are the objects given in them.

Any idea why he had to go that way in CPR? — Corvus

Kant was trying to save rationalism from Hume's sceptical challenges particularly wrt causation. Empiricism as hume developed it starts with something like, "Life is not an argument. Shit happens and minds have to try and make sense of it, get used to it and hope the sense will continue. " Rationalism always wants certainty in its ordering like an obsessive compulsive: retreating from reality precisely in order to make it conform to the logic of the mind - hence the contortions admirably laid out by @RussellA.

In order to establish what is named today, as I understand it, as Indirect Realism, still not accepted by the Direct Realists after 200 years of debate, including people such as Hilary Putnam and John Searle. — RussellA

Kant wrote CPR in order to investigate on Reason, and make secure footing for Metaphysics as Science. So he wasn't quite interested in idealism or realism, but he was more into proving into the limitations and capacities of Reason, and the legitimacy of Metaphysical knowledge i.e. how synthetic a priori knowledge is possible .

I don't think he was denying space and time for empirical reality at all. He presupposed it. But he had to postulate space and time as pure intuition in CPR in order to give ground for necessity of a priori knowledge such as Geometry and all the Metaphysical judgments, which are supposed to be superior to the natural science based on the space and time of the empirical reality. Inevitably Kant was a dualist.

Kant was trying to save rationalism from Hume's sceptical challenges particularly wrt causation. — unenlightened

Did he not oppose to both rationalism and empiricism? He wanted to combine the two schools, saying that both rationalism and empiricism lack in coherence in their perspective. He then set up his own system amalgamating the two, and proved Metaphysics has more legitimacy than Natural Science, because metaphysical knowledge is based a priori categories and pure intuitions.

….space and time and the matter within it are empirically real. — RussellA

….(not) denying space and time for empirical reality at all, but…presupposed it. — Corvus

Despite the direct textual references refuting that opinion, you both continue the misunderstanding. Or I do. One or the other.
————-

But he had to make space and time as pure intuition in order to give ground for necessity of a priori knowledge — Corvus

Absolutely. Why else to start a ~800 page treatise with something, re: sensibility, having nothing to do with the overall philosophical theme, re: reason.

If space and time are empirical realities they absolutely cannot be pure a priori conditions residing in the constitution of the subject, and if such were the case, that they are empirical realities, Kant could not justify them as antecedent conditions for anything of pure a priori content.

I might say, rather than being presupposed, the empirical reality of space and time was the standing hypothesis for the physics of the time, in which human knowledge was understood as being of things as they are in themselves. In which case, Kant’s entire academic exposure was in keeping with it, along with everyone else, and eventually becoming the starting point for refutation of that standing hypothesis.

Despite the direct textual references refuting that opinion, you both continue the misunderstanding. Or I do. One or the other. — Mww

If Kant's view on space and time was only pure intuitions, and there is no physical space and time as such, then he wouldn't have been taken seriously by the current philosophy or science. :)

If space and time are empirical realities they absolutely cannot be pure a priori conditions residing in the constitution of the subject, and if such were the case, that they are empirical realities, Kant could not justify them as antecedent conditions for anything of pure a priori content. — Mww

Kant was a dualist. Space and time was physical existence in empirical reality as well as pure intuitions for metaphysical knowledge. He had been only focusing on the latter in CPR.

Despite the direct textual references refuting that opinion, you both continue the misunderstanding — Mww

Is it the case that for Kant, space and time are empirically real?

In the Introduction to CPR by Paul Guyer and Allen W. Wood is the statement that, for Kant, space and time are empirically real.

Kant's thesis that space and time are pure forms of intuition leads him to the paradoxical conclusion that although space and time are empirically real, they are transcendentally ideal, and so are the objects given in them.

Kant writes that a transcendental idealist can be an empirical realist

A370 - The transcendental idealist, on the contrary, can be an empirical realist, hence, as he is called, a dualist, i.e., he can concede the existence of matter without going beyond mere self-consciousness and assuming something more than the certainty of representations in me, hence the cogito, ergo sum.

The SEP article on Kant's Transcendental Idealism writes that Kant was an Empirical Realist:
This provides a further sense in which Kant is an “empirical realist”

I would say that the above is some evidence that for Kant, as an Empirical Realist, space and time are empirically real.

If Kant's view on space and time was only pure intuitions, and there is no physical space and time as such, then he wouldn't have been taken seriously by recent science — Corvus

That argument may have some validity. In The Metaphysical Principles of Natural Science are the quite gentle objections, absent strict conclusive evidence, brought against Newton.

Kant was a dualist. Space and time was physical existence in empirical reality as well as pure intuitions for metaphysical knowledge. — Corvus

Those are not what Kant uses to describe himself as a dualist. Empirical reality yes; empirical reality of space and time, no. Empirical reality, that is, experience a posteriori, then, in juxtaposition to cognitive constructs, that is, pure thought a priori. THAT is the proper Kantian dualism.

a dualist, i.e., he can concede the existence of matter — RussellA

Exactly. Existence of matter. Things. Objects. That which appears to human sensibility. That of which sensation is possible. That for which phenomena are given. In Kant, space and time are none of those. And I warrant he more than merely concedes the reality of matter, but theorizes on the very necessity of it.

I would say that the above is some evidence that for Kant, as an Empirical Realist, space and time are empirically real. — RussellA

I understand you think that to be the case. The Critique, understood in its entirety as a system, disagrees with you.

Yup, I read that Kant has been taken seriously by the current scientists especially, because his idea on Space and Time is not just for empirical reality, but also for pure intuitions. This perspective of space and time warrants for more rigorous perception of the reality.

Scientists have been trying to find rationally justified warrant for infallible validity from their observations, theories, knowledge and claims on the reality out there, and they believe Kant's TI has it due to its dualism.

Observations on objects in the space of empirical reality alone has possibility of illusions. They want further verifications on their data by the pure space a priori intuitions, concepts and reasoning.

Exactly. Existence of matter. Things. Objects. That which appears to human sensibility. That of which sensation is possible. That for which phenomena are given. In Kant, space and time are none of those. — Mww

I agree that matter and space and time are different kinds of things, in that I can imagine space empty of matter, yet I cannot imagine matter not being in a space. But the fact they are different kinds of things does not mean they cannot both be real, albeit we only they are real transcendentally.

This doesn't answer Guyer's and Woods statement in the Introduction to the CPR that for Kant, space and time are empirically real.
Kant's thesis that space and time are pure forms of intuition leads him to the paradoxical conclusion that although space and time are empirically real, they are transcendentally ideal, and so are the objects given in them.

If we all accept that for Kant matter is empirically real, then how could it be the case that matter is empirically real yet the space and time that this matter is existing within is not empirically real?

What does it mean that the matter is real yet the space and time it exists within is not real?

Th only conclusion is that if matter is empirically real, then the space and time that it is existing within must also be empirically real.

In the Introduction to CPR by Paul Guyer and Allen W. Wood is the statement that, for Kant, space and time are empirically real. — RussellA

“…. Our expositions, consequently, teach the reality (i.e., the objective validity) of space….”
(B44, in….well, everybody)

Validity being, of course, a logical condition. So yes, space and time can be thought as empirically real, such that the extension of things has that which is extended into, making the shape and/or motion of things comprehensible, yet they are not in themselves empirically real.

Parenthesizing objective validity also dissipates the necessity of implementing the category of quality under which is subsumed the conception “reality”, all of which is the functional purview of understanding, the faculty of logic, which Kant isn’t yet considering. In addition, the use of objective in the exemption subsidizes the use of empirical, such that reality in 44 becomes empirical reality in 45.

Imagine how practically impossible it would be to talk about things, if it were denied from the outset such things were not, and could not, be thought as extended in space. From the perspective of the thesis itself, it was never meant to imply there actually is such a thing as space into which things extend, but only that the constitution of the human intellect can’t function without the transcendentally given objective validity granting it.

I don't think he was denying space and time for empirical reality at all. He presupposed it. But he had to postulate space and time as pure intuition in CPR in order to give ground for necessity of a priori knowledge such as Geometry and all the Metaphysical judgments, which are supposed to be superior to the natural science based on the space and time of the empirical reality. Inevitably Kant was a dualist. — Corvus

As you say, Kant wanted to combine the two schools of rationalism and empiricism.

However, not to show that Metaphysics is superior to the Natural sciences, but rather better explain both Metaphysics and the Natural Sciences. Neither Metaphysics nor the Natural Sciences could be properly understand without first amalgamating both rationalism and empiricism.

Kant's synthetic a priori amalgamating transcendental idealism and empirical realism is necessary to better understand both Metaphysics and the Natural Sciences. He was a dualist.

If we all accept that for Kant matter is empirically real, then how could it be the case that matter is empirically real yet the space and time that this matter is existing within is not empirically real? — RussellA

How could it be the case, that matter is real but space isn’t? That’s easy: come up with a whole bunch of ideas demonstrating how space isn’t real, let qualified investigators decide for themselves.

You know, like…..parts of space are just space, from which, incidentally, it acquires its ideality; space is no appearance or sensation or phenomenon, as do all real things; the space of a thing is one of two that cannot be thought away from the existence of a thing, hence cannot be the predicate in a judgement regarding what the thing is; space and time are not in the list of categories, hence are not, with respect to human understanding, necessary for the reality of things, but only for the knowledge of them. From which follows necessarily, that the knowledge of things is the determinant factor for their reality, the space of them utterly irrelevant, insofar as the thing must be whatever it is regardless of the space of it.

Better question might be….why does space have to be real? If you say, space is that which is contained in an empty bucket, what have you actually said? Even to say space is that which contains all things, doesn’t tell you a damn thing about any those things the totality of which is impossible for you anyway, which is the same as not knowing anything at all.

Imagine how practically impossible it would be to talk about things, if it were denied from the outset such things were not, and could not, be thought as extended in space. From the perspective of the thesis itself, it was never meant to imply there actually is such a thing as space into which things extend, but only that the constitution of the human intellect can’t function without the transcendentally given objective validity granting it. — Mww

I agree that it would be impossible to talk about things if we denied they could be extended in space, but it is Kant's position that there is in fact a space into which things extend.

From the SEP article section 2.3 on Kant’s Transcendental Idealism:
Kant in the Prolegomena was apoplectic that Feder and Garve had claimed that his Transcendental Idealism was just a Berkeleyan or Phenomenalist idealism, and pointed out that in the CPR bodies exist in space and that we have immediate, non-inferential knowledge of them. He pointed out that his idealism is merely a formal idealism, and it is only the form of objects that is due to our minds not the matter of the objects, in that the matter we experience depends on a source outside of the mind.

This does not mean that the matter in space we perceive as appearance is the same as the matter in space that exists outside our perception of it. For example, thinking about the analogy of colour, we perceive the colour red when looking at a wavelength of 700nm. Our perception of the colour red has been caused by the wavelength of 700nm, yet what we perceive, the colour red, is different to what caused it, a wavelength of 700nm.

We can talk about there being the colour red in the world even though the colour red doesn't exist in the word, yet although the colour red doesn't exist in the world there was something, a wavelngth of 700nm, that caused our perception of the colour red.

For Kant as a Empirical Realist, there has to be something in the world for us to be able to perceive something, but the something we perceive doesn't of necessity have to be the same thing as the something that caused our perception in the first place.

As you say, Kant wanted to combine the two schools of rationalism and empiricism. — RussellA

:up:

However, not to show that Metaphysics is superior to the Natural sciences, but rather better explain both Metaphysics and the Natural Sciences. Neither Metaphysics nor the Natural Sciences could be properly understand without first amalgamating both rationalism and empiricism. — RussellA

In the preface CPR, Kant sounds like he is on duty to reinstate Metaphysics as the queen of all Science.

Kant's synthetic a priori amalgamating transcendental idealism and empirical realism is necessary to better understand both Metaphysics and the Natural Sciences. He was a dualist. — RussellA

Kant's Space in TI of CPR is intuited pure concepts, and he is talking about how Metaphysics works. He is not talking about the space in empirical reality in CPR (it is presupposed existence). They are totally different things all together. If Kant denied the existence of the physical space in empirical reality, he would commit himself to an immaterial idealist like Berkeley. I don't see Kant would have done that at all. As you indicated, I agree, Kant was a dualist.

come up with a whole bunch of ideas demonstrating how space isn’t real..........From which follows necessarily, that the knowledge of things is the determinant factor for their reality, the space of them utterly irrelevant, insofar as the knowledge is remains regardless of the space of it.................If you say, space is that which is contained in an empty bucket, what have you actually said? — Mww

Space allows me to compare sizes. For example, the distance between the two sides of a garden bucket is less that the diameter of the Milky Way Galaxy.

If space wasn't real, then the garden bucket would be the same size as the Milky Way Galaxy.

In the preface CPR, Kant sounds like he is on duty to reinstate Metaphysics as the queen of all Science. — Corvus

To reinstate a scientific metaphysics in place of traditional metaphysics, from his position as Scientific Realist.

Introduction to CPR - Kant's position thus required him not only to undermine the arguments of traditional metaphysics but also to put in their place a scientific metaphysics of his own, which establishes what can be known a priori but also limits it to that which is required for ordinary experience and its extension into natural science.
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He is not talking about the space in empirical reality in CPR (it is presupposed existence). — Corvus

:up: As a thing-in-itself it cannot be talked about (like the Fight Club)