NOUMENO. — From the Greek νοοῦμενον (νοῦς, intellect), it means, etymologically, intelligible.
The term is used by Platone (v.) to refer 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). idea (v.) was regarded by Platone as true and subsistent reality, of which participation (v.). Kant, referring to the Platonic meaning, took up the term n. to designate the “thing or reality in itself” that lies beyond 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 also indispensable” (Prolegomeni, part 2, § 32; Italian translation by P. Carabellese, Messina 1942, pp. 126–27; cf. Critica della ragion pura, Logica trascendent., chap. 3, Italian translation, I, Bari 1910, pp. 248, 250). For Kant, this “reality in itself” is unknowable to the human intellect, which relates, through intuitions and concepts, only to sensible objects. He nevertheless distinguishes 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, designating, with predominantly Kantian reference, real being, reality, the “thing in itself” independent of knowledge.