Full Idea
With contraries it is not necessary if one exists for the other to exist too, for if everyone were well health would exist but not sickness, and if everything were white whiteness would exist but not black.
Gist of Idea
Both sides of contraries need not exist (as health without sickness, white without black)
Source
Aristotle (Categories [c.331 BCE], 14a06)
Book Reference
Aristotle: 'Categories and De Interpretatione', ed/tr. Ackrill,J.R. [OUP 1963], p.38