Full Idea
Two bodies are said to differ from one another, when something may be said of one of them, which cannot be said of the other at the same time.
Gist of Idea
Two bodies differ when (at some time) you can say something of one you can't say of the other
Source
Thomas Hobbes (De Corpore (Elements, First Section) [1655], 2.11.02)
Book Reference
Hobbes,Thomas: 'Metaphysical Writings', ed/tr. Calkins,Mary Whiton [Open Court 1905], p.81
A Reaction
Note the astute addition of 'at the same time'. Note also that it is couched in terms of what is true, rather than in terms of 'properties' or 'accidents'.