Full Idea
The cause of its being for everything is its substance.
Gist of Idea
The substance is the cause of a thing's being
Source
Aristotle (De Anima [c.329 BCE], 415b12)
A Reaction
It sounds as if 'substance' here means essence. We no longer see the cause of something's being as intrinsic to the thing. Only previous causes produce things. The 'form' must be the intrinsic cause of being.
Book Reference
Aristotle: 'De Anima (on the psuche)', ed/tr. Reeve, C.D.C. [Hackett 2017], p.27