Full Idea
On Aristotle's new theory it is forms that exist in their own right, whereas properties merely constitute the way forms of a certain kind are realized at some point of time in their existence.
Gist of Idea
Properties are just the ways in which forms are realised at various times
Source
report of Aristotle (Metaphysics [c.324 BCE], props) by Michael Frede - Substance in Aristotle's 'Metaphysics' p.80
Book Reference
Frede,Michael: 'Essays in Ancient Philosophy' [University of Minnesota 1987], p.80
A Reaction
I'm not sure that 'merely' gives us enough of a story here. I never understand the word 'realised' (or 'instantiated', come to that). What does x have to do to realise y? Is that a relation between a real and a non-real thing?