Note 13 — Chapter IV · DE INTERPRETATIONE.
Reading edition
Ibid. p. 17, a. 33: καὶ ἔστω ἀντίφασις τοῦτο, κατάφασις καὶ ἀπόφασις αἱ ἀντικείμεναι.
It seems (as Ammonius observes, Schol. p. 112, a. 33) that ἀντίφασις in this sense was a technical term, introduced by Aristotle.