Many posters has conflated the negative noumena with the positive noumena and do not understand what they are talking about with reference to Kant's CPR.
I have posted Kant's Chapter on Phenomena vs Noumena and has referred to it many times.
Kant: Phenomena vs Noumena [B294-B310]
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Kant: Phenomena vs Noumena [B306-B315]
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Since I have provided the appropriate reference from Kant, anyone who keep insisting in their own wrong interpretations of Kant is a numbskull and philosophical immature.
Note the relevant reference from Kant re Phenomena vs Noumena and what is noumena in the Negative and Positive Sense.
Kant in CPR wrote:1. B306 …, if we entitle certain Objects, as Appearances, Sensible entities 2 (Phenomena),
then since we thus distinguish the Mode in which we intuit them from the nature that belongs to them in-themselves,
it is implied in this distinction that we place the latter [in-themselves], considered in their own nature,
although we do not so intuit them, or that we place other Possible Things, which are not Objects of our Senses but are Thought as Objects merely through the Intellect,
in opposition to the former [Phenomena, Sensible entities],
and that in so doing we entitle them Intelligible Entities 1 (Noumena).
In the above, Kant identify Phenomena as Sensible Entities [verified empirically] while Noumena are Intelligible Entities [i.e. mere thought only].
5. And since the Intellect yields no Concepts additional to the Innate-Programs,
it {Intellect} also supposes that the Object-in-itself must at least be Thought through these Pure Concepts [Innate-Programs],
and so is misled into treating the entirely indeterminate Concept of an Intelligible entity, namely, of a something-in-General outside our Sensibility,
as being a Determinate Concept of an entity that allows of being known in a certain [purely Intelligible] manner by means of the Intellect.
The above point out how the Intellect confuses the noumena as a Determinate Concept.
To differentiate the noumena from the Phenomena we need to identify the noumena in the negative and positive sense.
6. If by 'Noumenon' we mean a Thing so far as it is not an Object of our Sensible Objectifying-Faculty, and so abstract from our Mode of Sensing it, {then} this is a Noumenon in the negative sense of the term.
If the noumena is to be related to the sensible phenomena, then this is a Noumenon in the negative sense, i.e. it can never be an sensible empirical object.
7. But if we understand by it [the thing] an Object of a non-Sensible Objectifying-Faculty,
we thereby presuppose a special Mode of Objectifying-Faculty, namely, the intellectual, which is not that which we possess, and of which we cannot comprehend even the Possibility. This would be 'Noumenon' in the positive sense of the term.
If the noumena is taken in the positive sense, then it has to be cognized with with an intellectual intuition which humans do no possess.
As such it is impossible to be real for any humans.
This noumena in the positive sense is the same as the assumption in science adopted by P-realists.
8. The Doctrine of Sensibility is likewise the Doctrine of the Noumenon in the negative sense, that is, of Things which the Intellect must think without this reference to our Mode of Objectifying-Faculty, therefore not merely as Appearances but as Things-in-Themselves. B308
As such when we consider the Doctrine of Sensibility with a sensible intuition, the noumenon is in the negative sense which the intellect can think of, but not to objectify the noumena.
So, when we deliberate on what is phenomena we can assume there is a corresponding noumena, this is taken in the
negativesense for theory sake. This is as best merely a thought and can never be something that is empirically real.
But to insist the noumena is a really real referent, this is taking the noumena in the
positive sense; this is an impossibility to be real because humans do not have the intelligible intuition to realize this intelligible object.