Individuatio fit per hanc materiam signatam. For materia signata see B. I, Chap. LXIII, p. 45, note. The doctrine that matter is the principle of individuation is one of the most intricate in the scholastic system, and cannot be entered upon here.
Things 'not actually intelligible' nevertheless are potentially intelligible: i.e., they lend themselves to a process of de- particularising under the active intellect; and so as universals become actual terms of intellect. This is explained at length in Chap. LXXVII.
Of God and His Creatures: 2.75