Full Idea
Not all understanding is demonstrative: rather, in the case of immediate items understanding is indemonstrable.
Gist of Idea
Some understanding, of immediate items, is indemonstrable
Source
Aristotle (Posterior Analytics [c.327 BCE], 72b19)
Book Reference
Aristotle: 'Posterior Analytics (2nd ed)', ed/tr. Barnes,Jonathan [OUP 1993], p.5
A Reaction
These are the foundations of Aristotle's epistemology, and I take it that they can be both empiricist and rationalist - sense experiences, and a priori intuitions.