Full Idea
The reason why all things are unities is indivisibility. In some, it is indivisibility with regard to movement, in others with regard to thought and the account.
Gist of Idea
Indivisibility is the cause of unity, either in movement, or in the account or thought
Source
Aristotle (Metaphysics [c.324 BCE], 1052a35)
Book Reference
Aristotle: 'Metaphysics', ed/tr. Lawson-Tancred,Hugh [Penguin 1998], p.286
A Reaction
This is puzzling, since Aristotle wasn't an atomist, and therefore thought that everything was endlessly divisible. He might better have said that unified things 'strongly resist division'.