Full Idea
If the principles are universal, they will not be primary beings [ousiai], ...but if the principles are not universal but of the nature of particulars, they will not be scientifically knowable. For scientific knowledge of any thing is universal.
Gist of Idea
Universal principles are not primary beings, but particular principles are not universally knowable
Source
Aristotle (Metaphysics [c.324 BCE], 1003a08)
Book Reference
Aristotle: 'Metaphysics', ed/tr. Lawson-Tancred,Hugh [Penguin 1998], p.76
A Reaction
Part of the fifteenth aporia (puzzle) of this book. Plato goes for the universal (and hence knowable), but Aristotle makes the particular primary, and so is left with an epistemological problem, which the rest of 'Metaphysics' is meant to solve.