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The noumenon (/ˈnɒmnɒn/) is a posited object or event that is known (if at all) without the use of ordinary sense-perception.[1][2] The term noumenon is generally used in contrast with, or in relation to phenomenon, which refers to anything that can be apprehended by, or is an object of the senses. Much of modern philosophy has generally been skeptical of the possibility of knowledge independent of the senses, and Immanuel Kant gave this point of view its canonical expression: that the noumenal world may exist, but it is completely unknowable through human sensation. In Kantian philosophy, the unknowable noumenon is often linked to the unknowable "thing-in-itself" (Ding an sich, which could also be rendered as "thing as such" or "thing per se"), although how to characterize the nature of the relationship is a question yet open to some controversy.


The Greek word νοούμενoν (nooúmenon), plural noumena (νοούμενα), is the middle-passive present participle of νοεῖν (noeîn), "I think, I mean", which in turn originates from the word nous (from νόος, νοῦς (noûs), "perception, understanding, mind"). A rough equivalent in English would be "something that is thought", or "the object of an act of thought".

Concept in pre-Kantian philosophy

Platonic Ideas and Forms are noumena, and phenomena are things displaying themselves to the senses. [...] that noumena and the noumenal world are objects of the highest knowledge, truths, and values is Plato's principal legacy to philosophy.

— The Oxford Companion to Philosophy [3]

In ancient Indian philosophy, concepts parallel to noumena and phenomena are found in the distinction between Brahman (cf. noumena) and Māyā (cf. phenomena).

Kant's usage


Noumenon came into its modern usage through Immanuel Kant. Its etymology derives from the Greek nooúmenon (thought-of) and ultimately reflects nous (intuition), but not emotion. Noumena is the plural form. Noumenon is distinguished from phenomenon (Erscheinung), the latter being an observable event or physical manifestation capable of being observed by one or more of the physical senses. The two words serve as interrelated technical terms in Kant's philosophy. As expressed in Kant's Critique of Pure Reason, human understanding is structured by "concepts of the understanding", or pure categories of understanding that the mind uses in order to make sense of raw unstructured experience.[4][5]

By Kant's account, when one employs a concept to describe or categorize noumena (the objects of inquiry, investigation or analysis of the workings of the world), one is employing a way of describing or categorizing phenomena (the observable manifestations of those objects of inquiry, investigation or analysis). Kant posited methods by which human beings make sense out of the interrelationships among phenomena: the concepts of the transcendental aesthetic, as well as that of the transcendental analytic, transcendental logic and transcendental deduction.[6][7][8] Taken together, Kant's "categories of understanding" are descriptions of the sum of human reasoning that can be brought to bear in attempting to understand the world in which we exist (that is, to understand, or attempt to understand, "things in themselves"). In each instance the word "transcendental" refers to the process that the human mind uses increasingly to understand or grasp the form of, and order among, phenomena. Kant asserts that to "transcend" a direct observation or experience is to use reason and classifications to strive to correlate with the phenomena that are observed. By Kant's view, humans can make sense out of phenomena in these various ways, but can never directly know the noumena, the "things-in-themselves", the actual objects and dynamics of the natural world. In other words, by Kant's Critique, our minds may attempt to correlate in useful ways, perhaps even closely accurate ways, with the structure and order of the various aspects of the universe, but cannot know these "things-in-themselves" (noumena) directly. Rather, we must infer the extent to which thoughts correspond with "things-in-themselves" by our observations of the manifestations of those things that can be perceived via the physical senses, that is, of phenomena.[9][10]

According to Kant, objects of which we are cognizant via the physical senses are merely representations of unknown somethings—what Kant refers to as the transcendental object—as interpreted through the a priori or categories of the understanding. These unknown somethings are manifested within the noumenon—although we can never know how or why as our perceptions of these unknown somethings via our physical senses are bound by the limitations of the categories of the understanding and we are therefore never able to fully know the "thing-in-itself".[11]

Noumenon and the thing-in-itself

Many accounts of Kant's philosophy treat "noumenon" and "thing-in-itself" as synonymous, and there is textual evidence for this relationship.[12] However, Stephen Palmquist holds that "noumenon" and "thing-in-itself" are only loosely synonymous, inasmuch as they represent the same concept viewed from two different perspectives,[13][14] and other scholars also argue that they are not identical.[15] Schopenhauer criticised Kant for changing the meaning of "noumenon". Opinion is far from unanimous.[16] Kant's writings show points of difference between noumena and things-in-themselves. For instance, he regards things-in-themselves as existing:

...though we cannot know these objects as things in themselves, we must yet be in a position at least to think them as things in themselves; otherwise we should be landed in the absurd conclusion that there can be appearance without anything that appears.[17]

..but is much more doubtful about noumena:

But in that case a noumenon is not for our understanding a special [kind of] object, namely, an intelligible object; the [sort of] understanding to which it might belong is itself a problem. For we cannot in the least represent to ourselves the possibility of an understanding which should know its object, not discursively through categories, but intuitively in a non-sensible intuition.[18]

A crucial difference between the noumenon and the thing-in-itself is that to call something a noumenon is to claim a kind of knowledge, whereas Kant insisted that the thing-in-itself is unknowable. Interpreters have debated whether the latter claim makes sense: it seems to imply that we know at least one thing about the thing-in-itself (i.e., that it is unknowable). But Stephen Palmquist explains that this is part of Kant's definition of the term, to the extent that anyone who claims to have found a way of making the thing-in-itself knowable must be adopting a non-Kantian position.[19]

Positive and negative noumena

Kant also makes a distinction between positive and negative noumena:[20][21]

If by 'noumenon' we mean a thing so far as it is not an object of our sensible intuition, and so abstract from our mode of intuiting it, this is a noumenon in the negative sense of the term.[22]

But if we understand by it an object of a non-sensible intuition, we thereby presuppose a special mode of intuition, 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.[23]

The positive noumena, if they existed, would roughly correspond with Plato's forms or ideas: immaterial entities that can only be apprehended by a special, non-sensory faculty: "intellectual intuition".[24]

Kant doubts that we have such a faculty, because for him intellectual intuition would mean that thinking of an entity, and its being represented, would be the same. He argues that humans have no way to apprehend the meaning of positive noumena:

Since, however, such a type of intuition, intellectual intuition, forms no part whatsoever of our faculty of knowledge, it follows that the employment of the categories can never extend further than to the objects of experience. Doubtless, indeed, there are intelligible entities corresponding to the sensible entities; there may also be intelligible entities to which our sensible faculty of intuition has no relation whatsoever; but our concepts of understanding, being mere forms of thought for our sensible intuition, could not in the least apply to them. That, therefore, which we entitle 'noumenon' must be understood as being such only in a negative sense.[25]

The noumenon as a limiting concept

Even if noumena are unknowable, they are still needed as a limiting concept,[26] Kant tells us. Without them, there would be only phenomena, and since potentially we have complete knowledge of our phenomena, we would in a sense know everything. In his own words:

Further, the concept of a noumenon is necessary, to prevent sensible intuition from being extended to things in themselves, and thus to limit the objective validity of sensible knowledge.[27]

What our understanding acquires through this concept of a noumenon, is a negative extension; that is to say, understanding is not limited through sensibility; on the contrary, it itself limits sensibility by applying the term noumena to things in themselves (things not regarded as appearances). But in so doing it at the same time sets limits to itself, recognising that it cannot know these noumena through any of the categories, and that it must therefore think them only under the title of an unknown something.[28]

Furthermore, for Kant, the existence of a noumenal world limits reason to what he perceives to be its proper bounds, making many questions of traditional metaphysics, such as the existence of God, the soul, and free will unanswerable by reason. Kant derives this from his definition of knowledge as "the determination of given representations to an object".[29] As there are no appearances of these entities in the phenomenal, Kant is able to make the claim that they cannot be known to a mind that works upon "such knowledge that has to do only with appearances".[30] These questions are ultimately the "proper object of faith, but not of reason".[31]

The dual-object and dual-aspect interpretations

Kantian scholars have long debated two contrasting interpretations of the thing-in-itself. One is the dual object view, according to which the thing-in-itself is an entity distinct from the phenomena to which it gives rise. The other is the dual aspect view, according to which the thing-in-itself and the thing-as-it-appears are two "sides" of the same thing. This view is supported by the textual fact that "Most occurrences of the phrase 'things-in-themselves' are shorthand for the phrase, 'things considered in themselves' (Dinge an sich selbst betrachten)."[32] Although we cannot see things apart from the way we do in fact perceive them via the physical senses, we can think them apart from our mode of sensibility (physical perception); thus making the thing-in-itself a kind of noumenon or object of thought.

Criticisms of Kant's noumenon

Pre-Kantian critique

Though the term noumenon did not come into common usage until Kant, the idea that undergirds it, that matter has an absolute existence which causes it to emanate certain phenomena, had historically been subjected to criticism. George Berkeley, who pre-dated Kant, asserted that matter, independent of an observant mind, is metaphysically impossible. Qualities associated with matter, such as shape, color, smell, texture, weight, temperature, and sound are all dependent on minds, which allow only for relative perception, not absolute perception. The complete absence of such minds (and more importantly an omnipotent mind) would render those same qualities unobservable and even unimaginable. Berkeley called this philosophy immaterialism. Essentially there could be no such thing as matter without a mind.[citation needed]

Schopenhauer's critique

Schopenhauer claimed that Kant used the word noumenon incorrectly. He explained in his "Critique of the Kantian philosophy", which first appeared as an appendix to The World as Will and Representation:

But it was just this distinction between abstract knowledge and knowledge of perception, entirely overlooked by Kant, which the ancient philosophers denoted by noumena and phenomena. (See Sextus Empiricus, Outlines of Pyrrhonism, Book I, Chapter 13, ' What is thought (noumena) is opposed to what appears or is perceived (phenomena).' ) This contrast and utter disproportion greatly occupied these philosophers in the philosophemes of the Eleatics, in Plato's doctrine of the Ideas, in the dialectic of the Megarics, and later the scholastics in the dispute between nominalism and realism, whose seed, so late in developing, was already contained in the opposite mental tendencies of Plato and Aristotle. But Kant who, in an unwarrantable manner, entirely neglected the thing for the expression of which those words phenomena and noumena had already been taken, now takes possession of the words, as if they were still unclaimed, in order to denote by them his things-in-themselves and his phenomena.[33]

The noumenon's original meaning of "that which is thought" is not compatible with the "thing-in-itself", the latter meaning things as they exist apart from their existence as images in the mind of an observer.[citation needed]

See also


  1. "1. intellectual conception of a thing as it is in itself, not as it is known through perception" "2. The of-itself-unknown and unknowable rational object, or thing-in-itself, which is distinguished from the phenomenon through which it is apprehended by the physical senses, and by which it is interpreted and understood; – so used in the philosophy of Kant and his followers."[dead link]
  2. "Noumenon | Definition of Noumenon by Webster's Online Dictionary". Retrieved September 10, 2015.<templatestyles src="Module:Citation/CS1/styles.css"></templatestyles>
  3. Honderich, Ted, ed. (31 August 1995). The Oxford Companion to Philosophy. Oxford University Press. p. 657. ISBN 0198661320. Retrieved 2014-10-28.<templatestyles src="Module:Citation/CS1/styles.css"></templatestyles>
  4. Hanna, Robert (2009). Completing the Picture of Kant's Metaphysics of Judgment. Stanford Encyclopedia of Philosophy.
  5. Stanford Encyclopedia of Philosophy on Kant's metaphysics.
  6. The Encyclopedia of Philosophy (Macmillan, 1967, 1996) Volume 4, "Kant, Immanuel", section on "Critique of Pure Reason: Theme and Preliminaries", p. 308 ff.
  7. The Encyclopedia of Philosophy (Macmillan, 1967, 1996) Volume 4, "Kant, Immanuel", section on "Transcendental Aesthetic", p. 310 ff.
  8. The Encyclopedia of Philosophy (Macmillan, 1967, 1996) Volume 4, "Kant, Immanuel", section on "Pure Concepts of the Understanding", p. 311 ff.
  9. See, e.g., The Encyclopedia of Philosophy (Macmillan, 1967, 1996) Volume 4, "Kant, Immanuel", section on "Critique of Pure Reason: Theme and Preliminaries", p. 308 ff.
  10. See also, e.g., The Encyclopedia of Philosophy (Macmillan, 1967, 1996) Volume 4, "Kant, Immanuel", section on "Pure Concepts of the Understanding", p. 311 ff.
  11. Critique of Pure Reason A256/B312, p. 27
  12. Immanuel Kant (1781) Critique of Pure Reason, for example in A254/B310, p. 362 (Guyer and Wood), "The concept of a noumenon, i.e., of a thing that is not to be thought of as an object of the senses but rather as a thing-in-itself [...]"; But note that the terms are not used interchangeably throughout. The first reference to thing-in-itself comes many pages (A30) before the first reference to noumenon (A250). For a secondary or tertiary source, see: "Noumenon" in the Encyclopædia Britannica
  13. "Noumenon: the name given to a thing when it is viewed as a transcendent object. The term 'negative noumenon' refers only to the recognition of something which is not an object of sensible intuition, while 'positive noumenon' refers to the (quite mistaken) attempt to know such a thing as an empirical object. These two terms are sometimes used loosely as synonyms for 'transcendental object' and 'thing-in-itself', respectively. (Cf. phenomenon.)" – Glossary of Kant's Technical Terms
  14. Thing-in-itself: an object considered transcendentally apart from all the conditions under which a subject can gain knowledge of it via the physical senses. Hence the thing-in-itself is, by definition, unknowable via the physical senses. Sometimes used loosely as a synonym of noumenon. (Cf. appearance.)" – Glossary of Kant's Technical Terms. Palmquist defends his definitions of these terms in his article, "Six Perspectives on the Object in Kant's Theory of Knowledge", Dialectica 40:2 (1986), pp.121–151; revised and reprinted as Chapter VI in Palmquist's book, Kant's System of Perspectives (Lanham: University Press of America, 1993).
  15. Oizerman, T. I., "Kant's Doctrine of the "Things in Themselves" and Noumena", Philosophy and Phenomenological Research, Vol. 41, No. 3, Mar., 1981, 333–350; Karin de Boer, "Kant's Multi-Layered Conception of Things in Themselves, Transcendental Objects, and Monads", Kant-Studien 105/2, 2014, 221-260.
  16. "Other interpreters have introduced an almost unending stream of varying suggestions as to how these terms ought to be used. A handful of examples will be sufficient to make this point clear, without any claim to represent an exhaustive overview. Perhaps the most commonly accepted view is expressed by Paulsen, who equates 'thing-in-itself' and 'noumenon', equates 'appearance' and 'phenomenon', distinguishes 'positive noumenon' and 'negative noumenon', and treats 'negative noumenon' as equivalent to 'transcendental object' [pp. 4:148-50, 154-5, 192]. Al-Azm and Wolff also seem satisfied to equate 'phenomenon' and 'appearance', though they both carefully distinguish 'thing-in-itself' from 'negative noumenon' and 'positive noumenon' [A4:520; W21:165, 313–5; s.a. W9:162]. Gotterbarn similarly equates the former pair, as well as 'thing-in-itself' and 'positive noumenon', but distinguishes between 'transcendental object', 'negative noumenon' and 'thing-in-itself' [G11: 201]. By contrast, Bird and George both distinguish between 'appearance' and 'phenomenon', but not between 'thing-in-itself' and 'noumenon' [B20:18,19, 53–7; G7:513-4n]; and Bird sometimes blurs the distinction between 'thing-in-itself' and 'transcendental object' as well.[2] Gram equates 'thing-in-itself' not with 'noumenon', but with 'phenomenon' [G13:1,5-6]! Allison cites different official meanings for each term, yet he tends to equate 'thing-in-itself' at times with 'negative noumenon' and at times with 'transcendental-object', usually ignoring the role of the 'positive noumenon' [A7:94; A10:58,69]. And Buchdahl responds to the fact that the thing-in-itself seems to be connected with each of the other object-terms by regarding it as 'Kant's umbrella term'.[3]" Stephen Palmquist on Kant's object terms
  17. Critique of Pure Reason Bxxvi-xxvii.
  18. Critique of Pure Reason A256, B312, p. 273 (NKS)
  19. "The Radical Unknowability of Kant's 'Thing in Itself'", Cogito 3:2 (March 1985), pp.101–115; revised and reprinted as Appendix V in Stephen Palmquist, Kant's System of Perspectives (Lanham: University Press of America, 1993).
  20. Mattey, G.J
  21. Lecture notes by G.J Mattey
  22. Critique of Pure Reason A250/B307, p. 267 (NKS)
  23. Critique of Pure Reason A250/B30, p. 2677 (NKS)
  24. "The noumena are ‘forms’ or ‘ideas’, which exist in a realm beyond space and time." University of Leeds course notes
  25. Critique of Pure Reason B309, p. 270 (NKS)
  26. Allison, H. "Transcendental Realism, Empirical Realism, and Transcendental Idealism".<templatestyles src="Module:Citation/CS1/styles.css"></templatestyles>
  27. Critique of Pure Reason A253/B310
  28. Critique of Pure Reason A256/B312, p. 273
  29. Critique of Pure Reason B/137, p. 156
  30. Critique of Pure Reason B/xx., p. 24
  31. Rohmann, Chris. "Kant" A World of Ideas: A Dictionary of Important Theories, Concepts, Beliefs, and Thnkers. Ballantine Books, 1999.
  32. Mattey, GJ. Lecture Notes on the Critique of Pure Reason
  33. The World as Will and Representation(vol. 1, Dover edition 1966, ISBN 0-486-21761-2 p. 476-477)

External links