Full Idea
Aristotle describes form or essence as the cause of there being an actual individual substance, and as the cause of its being a unity rather than a heap.
Gist of Idea
Essence is the cause of individual substance, and creates its unity
Source
report of Aristotle (Metaphysics [c.324 BCE], ess) by Charlotte Witt - Substance and Essence in Aristotle Intro
Book Reference
Witt,Charlotte: 'Substance and Essence in Aristotle' [Cornell 1994], p.3
A Reaction
Wiggins defends the species-essence view (Idea 12068) by preferring the 'secondary substance' account in 'Categories' to Aristotle's ideas about 'form' which emerge later in 'Metaphysics'. I prefer Witt to Wiggins.
Related Idea
Idea 12068 Standardly, Aristotelian essences are taken to be universals of the species [Aristotle, by Witt]