Full Idea
That from which the implication of existence does not hold reciprocally is thought to be prior.
Clarification
'Prior' usually means 'has to come first in a sequence of reasoning'
Gist of Idea
A thing is prior to another if it implies its existence
Source
Aristotle (Categories [c.331 BCE], 14a32)
Book Reference
Aristotle: 'Categories and De Interpretatione', ed/tr. Ackrill,J.R. [OUP 1963], p.39
A Reaction
shadows and objects