Full Idea
Of the thing understood all that is within the actually understanding intellect is the abstracted intelligible species.
Gist of Idea
Understanding consists entirely of grasping abstracted species
Source
Thomas Aquinas (Summa Theologicae [1265], Q85 Art2)
Book Reference
Aquinas,Thomas: 'Treatise on Human Nature (Summa 1a 75-89)', ed/tr. Pasnau,Robert [Hackett 2002], p.162
A Reaction
Abstraction is never supposed to be a luxury bolt-on, but is always seen (in this tradition, and presumably in the modern one), as essential to the intellect, and its way of coming to understand the world. Aristotelian definition is behind this idea.