Full Idea
Our imagination and senses grasp only the outer properties of things, not their natures. ...Understanding, however, grasps the very substance and nature of things, so that what is represented in understanding is a likeness of thing's very essence.
Gist of Idea
Senses grasp external properties, but the understanding grasps the essential natures of things
Source
Thomas Aquinas (Quodlibeta [1267], 8.2.2)
Book Reference
McDermott,Timothy: 'Aquinas: how to read' [Granta 2007], p.20
A Reaction
This is exactly the picture I endorse for modern science. Explanation is the path to understanding, and that must venture beyond immediate experience.