In all commentaries on Kant's philosophy and his Critique of Pure Reason, it is stated that noumenon is completely unknowable. For example in the entry of 'Appearance' in Encyclopaedia Britannica we see:

... Immanuel Kant created the term noumenon to signify unknowable reality, which he distinguished from phenomenon, the appearance of reality.

But at the same time we see in the same commentaries that space, time and causality are ascribed to phenomenon AND NOT the noumenon. Then, is it not the case that although Kant claims the noumenon to be unknowable, he is in a sense describing it indirectly? I mean how the noumenon is unknowable reality and at the same time we can say for example:

Time can characterize only phenomena; it could not characterize the noumenal.

(The Philosophy of Schopenhauer by Bryan Magee p.128)

  • 2
    To be exact: The pure categories (including causality) apply to noumena as well since they are about the relations between possible objects of thought. People like Allison and Ameriks are quite explicit about this. Nevertheless, the point is that there can be no material positive theoretical knowledge about any particular noumenon. Formal (and negative) relations, like causality and e.g. the Moral Law, do explicitly apply to them.
    – Philip Klöcking
    Commented Feb 24, 2019 at 18:20
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    Another nitpick, but this is a common mistake: The question whether noumena are transcendentally real or ideal is subject of discussion. I, personally, am on the "Kant is agnostic in ontological judgements regarding noumena" side. And it is quite obvious that Kant repeatedly writes that reality is only what can be credited for in experience.
    – Philip Klöcking
    Commented Feb 24, 2019 at 18:24
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    Whatever Magee's merits as a commentator on Schopenhauer, he is not an expert on Kant. You would do better to follow up on PK's advice and consult H.E. Allison, Kant's Transcendental Idealism: An Interpretation and Defense, ISBN 10: 0300036299 / ISBN 13: 9780300036299. Published by Yale University Press, 1986. And K. Ameriks, Kant's Theory of Mind: An Analysis of the Paralogisms of Pure Reason, ISBN 10: 0198246617 / ISBN 13: 9780198246619. Published by Oxford University Press, 1982.
    – Geoffrey Thomas
    Commented Feb 24, 2019 at 19:21
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    In dreams of a spirit seer Kant more directly (than CPR) describes the noumenon as knowable mystically thanks to his encounter with Swedenborg repository.hkbu.edu.hk/cgi/… but these matters are hardly knowable(!) to me
    – Rushi
    Commented Feb 25, 2019 at 3:50
  • It is a well-known contradiction in Kant's views, which was spotted as early as Fichte: for how unknowable "thing in itself" is supposed to be Kant shouldn't be talking about it at all. But, although things in themselves and noumena are often conflated in popular expositions, Kant distinguishes between the two. Noumena are "ideal elements" that reason adds to "round out" the experience, so it is more excusable to talk about them. See Palmquist's Two Perspectives on the Object of Knowledge on the distinction.
    – Conifold
    Commented Feb 25, 2019 at 5:34


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