The noumenon pron.: // is a posited object or event that is known (if at all) without the use of the senses. The term is generally used in contrast with, or in relation to "phenomenon", which refers to anything that appears to, or is an object of, the senses. In Ancient philosophy, the noumenal realm was equated with the world of ideas known to the philosophical mind, in contrast to the phenomenal realm, which was equated with the world of sensory reality, known to the uneducated mind. 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 classical version, saying that the noumenal world may exist, but it is completely unknowable to humans. In Kantian philosophy the unknowable noumenon is often linked to the unknowable "thing per se" (Ding an sich), although how to characterize the nature of the relationship is a question yet open to some controversy.
The Greek word Noumenon (νοούμενoν), plural noumena (νοούμενα), is the middle-passive present participle of νοεῖν (noein), "I think, I mean", which in turn originates from the word "nous" (from νόος, νοῦς, perception, understanding, mind). A rough equivalent in English would be "something that is thought", or "the object of an act of thought".
Usage in reference to 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 
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). 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 human 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 innate categories that the mind uses in order to make sense of raw unstructured experience.
By Kant's account, when we employ a concept to describe or categorize noumena (the objects of inquiry, investigation or analysis of the workings of the world), we are in fact 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. 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 sensed, that is, of phenomena.
According to Kant, objects of which we are sensibly cognizant 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 are bound by the limitations of the categories of the understanding and we are therefore never able to fully know the "thing-in-itself".
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. However, Stephen Palmquist holds that "noumenon" and "thing-in-itself" are only loosely synonymous in as much as they represent the same thing but viewed from two different perspectives, and other scholars also argue that they are not identical. Schopenhauer criticised Kant for changing the meaning of "noumenon". Opinion is far from unanimous. 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."
..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".
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.
Positive and negative noumena 
Kant also makes a distinction between positive and negative noumena
"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".
"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."
The positive noumena, if they existed, would roughly correspond with Plato's Forms or Idea—immaterial entities which can only be apprehended by a special, non-sensory, faculty: "intellectual intuition".
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.
The noumenon as a limiting concept 
Even if noumena are unknowable, they are still needed as a limiting concept, Kant tells us. Without them, there would be only phenomena, and since 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".
"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".
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." 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." These questions are ultimately the "proper object of faith, but not of reason."
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 a distinct entity from the phenomena it gives rise to. The other is the dual aspect view, according to which the thing-in-itself and the thing-as-it-appears to us 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)." Although we cannot see things apart from the way we do in fact see them, we can think them apart from our mode of sensibility (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, was metaphysically impossible. Qualities associated with matter, such as shape, color, smell, texture, weight, temperature, and sound were all dependent on minds, which allowed 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.
Schopenhauer's critique 
"But it was just this difference 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."
The Noumenon's original meaning of "that which is thought" is not compatible with the "thing–in–itself", which signifies things as they exist apart from being images in the mind of an observer.
Nietzsche's critique 
Friedrich Nietzsche, having been profoundly influenced by Schopenhauer's work, went on to criticise Kant's noumenon on slightly different grounds. He later similarly criticised Schopenhauer's work. Nietzsche found fault in the noumenon's lack of definite properties and its complete inability to interact with other things. He argued that a thing in itself would necessarily be outside of any causal chain since it cannot interact with any other things without demonstrating other properties than being the "ground of being". Nietzsche and later philosophers argued that the noumenon is of an utterly indeterminate nature and that any discussion that does not treat it as such cannot, in fact, be a discussion of the noumenon. In demonstrating any definite properties, the noumenon would cease to be so. Nietzsche's criticism of the noumenon can be found, for example, in his Beyond Good and Evil.
Nietzsche provided increasingly sophisticated accounts of the noumenon throughout the body of his work by explaining its numerous influences and connections with other ideas. An example of such comment can be found in his criticisms of materialistic atomism and what he called "soul-atomism", which follows Nietzsche's belief that synthetic judgments a priori are impossible. From the first chapter of Beyond Good and Evil:
"[I]t is high time to replace the Kantian question, 'How are synthetic judgments a PRIORI possible?' by another question, 'Why is belief in such judgments necessary?'--in effect, it is high time that we should understand that such judgments must be believed to be true, for the sake of the preservation of creatures like ourselves; though they still might naturally be false judgments! Or, more plainly spoken, [...] synthetic judgments a priori should not "be possible" at all [...]"
Nietzsche then asserts that "the atomism of the soul" is connected with a belief in the existence of the thing in itself. He then attempts precisely to define that particular type of atomism:
"Let it be permitted to designate by [the atomism of the soul] the belief which regards the soul as something indestructible, eternal, indivisible, as a monad, as an atomon: this belief ought to be expelled from science!".
In arguing that the concept of the noumenon negatively influenced other ideas in specific ways, Nietzsche specifically characterized it in those ways.
Though Nietzsche was critical of theories concerning what could not be observed, he believed that theories ought to be capable of being falsified: while arguing against what he held to be the negative influence of the Kantian noumenon in the philosophy and science of his day, Nietzsche roughly approximated the scientific philosopher Karl Popper's assertion that falsifiability was the basis of scientific knowledge:
"One can sum up all this by saying that the criterion of the scientific status of a theory is its falsifiability, or refutability, or testability."
Nietzsche wrote in the eighteenth section of the first chapter of Beyond Good and Evil that
"It is certainly not the least charm of a theory that it is refutable; it is precisely thereby that it attracts the more subtle minds."
References in Popular Culture 
- Tao Lin references, discusses & appears to support the idea of noumenon in his essay on the state of the novel.
- "He had never indulged in the search for the True Substance, the One, the Absolute, the Diamond suspended from the Christmas Tree of the Cosmos. He had always felt the faint ridicule of a finite mind peering at the iridescence of the invisible through the prison bars of integers. And even if the Thing could be caught, why should he, or anybody else for that matter, wish the phenomenon to lose its curls, its mask, its mirror, and become the bald noumenon?"
See also 
- Schopenhauer's criticism of the Kantian philosophy
- Transcendental idealism
- "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 senses, and by which it is interpreted and understood; – so used in the philosophy of Kant and his followers."
- "Platonist frames of thought draw a dividing line between two realms. One realm, the inferior of the two, is the material, physical world of sense experience. It is the "phenomenal" world, the world of objects, of the body, of immediate perception. The other, superior realm is the world of the immaterial, the spiritual, the world of realities not accessible to the body's senses, the world known by intellect or spiritual sense, the "noumenal" world."
- Honderich, E. (Ed). The Oxford Companion to Philosophy
- Hanna, Robert (2009). Completing the Picture of Kant's Metaphysics of Judgment. Stanford Encyclopedia of Philosophy.
- The Encyclopedia of Philosophy (Macmillan, 1967, 1996) Volume 4, "Kant, Immanuel", section on "Critique of Pure Reason: Theme and Preliminaries", p308 ff.
- The Encyclopedia of Philosophy (Macmillan, 1967, 1996) Volume 4, "Kant, Immanuel", section on "Transcendental Aesthetic", p310 ff.
- The Encyclopedia of Philosophy (Macmillan, 1967, 1996) Volume 4, "Kant, Immanuel", section on "Pure Concepts of the Understanding", p311 ff.
- See, e.g., The Encyclopedia of Philosophy (Macmillan, 1967, 1996) Volume 4, "Kant, Immanuel", section on "Critique of Pure Reason: Theme and Preliminaries", p308 ff.
- See also, e.g., The Encyclopedia of Philosophy (Macmillan, 1967, 1996) Volume 4, "Kant, Immanuel", section on "Pure Concepts of the Understanding", p311 ff.
- Critique of Pure Reason A256/B312,P27
- Immanuel Kant (1781) Critique of Pure Reason, for example in A254/B310,P362 (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 to noumenon (A250). For a secondary or tertiary source, see: "Noumenon" in Encyclopædia Britannica
- "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
- Thing in itself: an object considered transcendentally apart from all the conditions under which a subject can gain knowledge of it. Hence the thing in itself is, by definition, unknowable. 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).
- 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.
- "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' [P4:148-50,154-5,192]. 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. 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'." Stephen Palmquist on Kant's object terms
- Critique of Pure Reason Bxxvi-xxvii.
- Critique of Pure Reason A256,B312,p273(NKS)
- "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).
- Mattey, G.J
- Critique of Pure Reason A250/B307,P267(NKS)
- Critique of Pure Reason A250/B30,P2677(NKS)
- "The noumena are ‘forms’ or ‘ideas’, which exist in a realm beyond space and time." University of Leeds course notes
- Critique of Pure Reason B309,P270(NKS)
- Allison, H. "Transcendental Realism, Empirical Realism, and Transcendental Idealism".
- Critique of Pure Reason A253/B310
- Critique of Pure Reason A256/B312,P273
- Critique of Pure Reason B/137,P156
- Critique of Pure Reason B/xx.,P24
- Rohmann, Chris. "Kant" A World of Ideas: A Dictionary of Important Theories, Concepts, Beliefs, and Thnkers. Ballantine Books, 1999.
- Mattey, GJ. Lecture Notes on the Critique of Pure Reason
- The World as Will and Representation(vol. 1, Dover edition 1966, ISBN 0-486-21761-2 p. 476-477)
- Nietzsche, F. Beyond Good and Evil, Chapter 1. section 11.
- Nietzsche, F. Beyond Good and Evil Chapter 1. Section 12.
- Popper, K. Science: Conjectures and Refutations
- Nietzsche, F. Beyond Good and Evil. Chapter 1, Section 18.
- Tao Lin Wants To Understand Your Noumenon(Melville House Books)
- The surd of metaphysics; an inquiry into the question: Are there things-in-themselves? (1903) Paul Carus, 1852–1919 Retrieved May 18, 2012
- Stanford Encyclopedia of Philosophy on Kant's metaphysics.
- Glossary of Kant's technical terms by Stephen Palmquist
- Article from undergraduate journal Noesis
- Lecture notes by G.J Mattey
- Kant's System of Perspectives (Lanham: University Press of America, 1993) by Stephen Palmquist