Note 14 — Chapter XXVII · PARMENIDES.
Reading edition
Plato, Parmenid. p. 132 B. μὴ τῶν εἰδῶν ἕκαστον ᾖ τούτων νοήμα, καὶ οὐδαμοῦ αὐτῷ προσήκη ἐγγίγνεσθαι ἄλλοθι ἢ ἐν ψυχαῖς.… Τί οὖν; φάναι, ἓν ἕκαστόν ἐστι τῶν νοημάτων, νόημα δὲ οὐδενός; Ἀλλ’ ἀδύνατον, εἰπεῖν. Ἀλλὰ τινός; Ναί. Ὄντος ἢ οὐκ ὄντος; Ὄντος. Οὐχ ἑνός τινος, ὃ ἐπὶ πᾶσιν ἐκεῖνο τὸ νόημα ἐπὸν νοεῖ, μίαν τινὰ οὖσαν ἰδέαν; Ναί.
Aristotle (Topic. ii. 113, a. 25) indicates one way of meeting this argument, if advanced by an adversary in dialectic debate — εἰ τὰς ἰδέας ἐν ἡμῖν ἔφησεν εἶναι.