Full Idea
The forms of sensible substances are not pure actualities; they in part are constituted by unrealized possibilities and in that sense are not fully real.
Gist of Idea
Forms of sensible substances include unrealised possibilities, so are not fully actual
Source
report of Aristotle (Metaphysics [c.324 BCE], Z) by Michael Frede - Aristotle's Conception of Metaphysics p.90
Book Reference
Frede,Michael: 'Essays in Ancient Philosophy' [University of Minnesota 1987], p.90
A Reaction
Frede suggests that the form of the Unmoved Mover is the ideal case, because it is fully actual. I like the present idea, because it includes modal truths (i.e. dispositions and powers) in the form which gives a thing its nature.