Full Idea
Being is inherently intellect's most intelligible object, in which it finds the basis of all conceptions. ...All of intellect's other conceptions must be arrived at by adding to being, insofar as they express what is not expressed by 'being' itself.
Gist of Idea
Being is basic to thought, and all other concepts are additions to being
Source
Thomas Aquinas (Disputed questions about truth [1267], I.1c), quoted by Kretzmann/Stump - Aquinas, Thomas 09
Book Reference
'Shorter Routledge Encyclopaedia of Philosophy', ed/tr. Craig,Edward [Routledge 2005], p.37
A Reaction
I like the word 'intelligible' here. We might know reality, or be aware of appearances, but what is intelligible lies nicely in between. What would Berkeley make of that? I presume 'intelligible' means 'makes good sense'.