NOUMENON. - From the Greek νοοῦμενον (νοῦς, intellect) it means, etymologically, intelligible.
The term is referred by Plato (v.) to the species or ideas "not perceptible by us through the senses, but only through the intellect" (ἀναλώσῃς ὡς ὄψων εἰς δὲ) νοοῦμενον μόνον, Tim., 51 d, cf. Resp., 508). The idea (v.) was taken by Plato as a true and subsistent reality of which the sensible appearances are an imitation and participation (v.). Kant, referring to the Platonic meaning, took up the term n. to indicate the "thing or reality in itself" that lies beyond the objects of the senses as phenomena: "we may say that the representation of such beings which are the foundation of phenomena, and therefore of pure intelligible beings, is not only admissible but even indispensable" (Prolegomena, part 2, § 32; Ital. trans. by P. Carabellese, Messina 1942, pp. 126-27; cf. Critique of Pure Reason, Transcendental Logic, ch. 3, Ital. trans., I, Bari 1910, pp. 248, 250). Such "reality in itself" is, for Kant, unknowable to the human intellect, which relates only, through intuitions and concepts, to sensible objects. He distinguishes, however, between n. in the negative sense ("a thing insofar as it is not an object of our sensible intuition") and n. in the positive sense ("the object of a non-sensible, that is, intellectual intuition, which, however, is not ours and whose possibility we cannot even comprehend"), ibid., p. 249): n. is therefore, for theoretical human knowledge, which cannot go beyond phenomena, "only a limiting concept (Grenzbegriff)" (ibid., p. 251). The term has remained in philosophical language, indicating, with a predominantly Kantian reference, real being, reality, the "thing in itself" independent of knowledge.
Bibliography
Ugo Viglino