A term used by philosophers, and mainly by Kantians, to designate objects that cannot be sensibly perceived and can only be mentally apprehended. This article sketches the pre-Kantian usages and then explains and criticizes the place of the term in kantianism.
Pre-Kantian Usages. The word noumena (Gr. νοούμενα) is encountered in plato in several passages (Rep. 508C, 509D; Parm. 132C; Tim. 30D, 51D) and designates ideas of which it is said explicitly that they can be grasped only mentally and not sensibly (Rep. 507B; Tim. 51D). The only things accessible to sensible visualization, for Plato, are those that are subject to multiplicity and becoming; these do not exist in the full sense of the word, and form the τóπος ὁρατóς (Rep. 532D). The Ideas, on the contrary, constitute the τóπος νοητóς (Rep. 508C) and are the only true being (Phaedrus 247C, 249C; Tim. 28A), which, as such, is eternal and immutable and can be apprehended only mentally by reminiscence and dialectics. This is especially true of the original source of all ideas, of absolute goodness and absolute beauty—the beautiful and good in every respect that fully encompass all beauty and goodness (Symp. 210E-211D; Rep. 509B).
In Aristotle, the term noumena is encountered in one passage only (Meta. 1074b 36–1075a 5), where it is used three times; elsewhere, the term νοητά is employed in the same sense (e.g., Anim. 431b 20–432a 14). More specifically, Aristotle distinguishes what can be mentally comprehended from what can be sensibly perceived; on actuation, the latter coincides with sense perception in the same way as the former with simple apprehension (Meta. 1075a 3–5; Anim. 431b 22–23). Contrary to Plato, Aristotle holds that what can be apprehended only mentally is not separated from sensible phenomena, but is contained in phenomena and is to be sought in them (Anim. 432a 3–5). Thus the mind extracts essences from visible things (ibid. 431b 2); the essential forms inherent in such things therefore take the place of Plato's transcending Ideas. The apprehension of the noumena, which is a kind of intuition in Plato, appears thus as an abstraction in Aristotle. It is perfected by a reasoning process that ascends to the highest noumena, i.e., the Divine as eternal, immovable, and separate (Meta. 1026a 10–30).
St. thomas aquinas, working through St. augustine as an intermediary, effected a synthesis of Plato and Aristotle. The noumena inherent in things (intelligibilia ) are essences, and, above all, being; they are grasped by abstraction. Their bases, as transcendental noumena, are the archetypal ideas of the divine intellect, which, in turn, are founded upon the archnoumenon, i.e., upon God as the subsistent being; man ascends to this conclusion by metaphysical discourse.
Kantian Notion. According to I. Kant, noumena must be distinguished from phenomena; the latter are called "phenomena, in so far as they are thought as objects according to the unity of the categories" (Critique of Pure Reason A 248). In this text, as opposed to ordinary usage, phenomena are distinguished from appearances; the distinction, however, must be correctly understood. When one says: "The senses represent objects as they appear, the understanding as they are, the latter statement" must "be understood in the empirical meaning" (ibid. A 258), i.e., as objects-for-man. On the contrary, the term "noumena (intelligibilia )" is applied to those things "which are merely objects of understanding, and which, nevertheless, can be perceived as such by intuition, though not by sensible intuition (therefore, coram intuitu intellectuali )" (ibid. A 249). Man's concepts themselves can never determine an object; for this purpose, an intuition is needed to supplement such concepts, and for man this can only be sensible. Man has no intellectual intuition that would make possible the "transcendental use" of his concepts, i.e., a use that would reach the thing-in-itself "beyond the sphere of possible experience" (ibid. A 248). The noumena are ordered to this usage, which is "not contradictory" (ibid. A 254), since they are "merely a limiting concept" (ibid. A 255); one encounters them not as "intelligible objects" but merely as "a problem" (ibid. A 256). But they are not an "arbitrary invention" (ibid. A 255); on the contrary, they are "necessary" (ibid. A 254), although only of "negative use" (ibid. A 255) "in order to impose a limit upon the presumptions of sensibility" (ibid. ). Here, moreover, one should "prevent sensible intuition from being extended to things in themselves," and one should not claim that "sensibility is the only possible mode of intuition" (ibid. A254). As a consequence, "our understanding attains in this way a sort of negative extension, i.e., it is not limited by, but rather limits, sensibility by giving the name of noumena to things, not considered as phenomena, but as things in themselves. But our understanding imposes also limits upon itself, recognizing that it cannot know these noumena by means of the categories; hence, it is compelled to think of them merely as of an unknown something" (ibid. A 256).
Beyond this usage lies that of the moral order, which shows man "as a being endowed with internal freedom (homo noumenon )" (Metaphysik der Sitten, Berlin Academy ed., 6:418), and which can give to his "causality as a noumenon" (Critique of Practical Reason ; ibid. 5:50) "for the first time objective, although only practical, reality" (ibid. 48).
By way of evaluation, it may be said that Kant loses the synthesis characteristic of Aquinas by disregarding the process of abstraction that obtains the noumena, i.e., essences and being, from the phenomena. At the same time, he returns to Plato by assuming that the noumena are accessible to intellectual intuition alone, an accessibility that he justly denies to man.
See Also: criticism, philosophical; knowledge, theories of
Bibliography: i. kant, Prolegomena, §§32–35. r. eisler, Wörterbuch der philosophischen Begriffe, 3 v. (4th ed. Berlin 1927–30) 2:271–73. f. c. copleston, History of Philosophy (Westminster, Md. 1946–) 6:267–72. a. carbini, Enciclopedia filosofica, 4 v. (Venice-Rome 1957) 3:940–42.
[j. b. lotz]