Full Idea
The intellect first apprehends the quiddity of a thing. ...Then it acquires the properties, accidents and dispositions associated with the thing's essence. It must proceed from one compounding or dividing of aspects to another, which is reasoning.
Clarification
'Quiddity' is 'whatness', its universal nature
Gist of Idea
First grasp what it is, then its essential features; judgement is their compounding and division
Source
Thomas Aquinas (Summa Theologicae [1265], Ia.Q85 5c), quoted by Kretzmann/Stump - Aquinas, Thomas 11
Book Reference
'Shorter Routledge Encyclopaedia of Philosophy', ed/tr. Craig,Edward [Routledge 2005], p.40
A Reaction
[compressed] Tracking the process of acquiring knowledge of a thing (rather than necessary and sufficient conditions for full knowledge) is closer to Quine's naturalised epistemology than to the standard analytic approach to the concept of knowledge.