Full Idea
We can say that the form that gives corporeal bulk [molem] or extension to things is the essential nature of quantity. To have bulk is to expel a similar bulk from the same space.
Gist of Idea
We can get at the essential nature of 'quantity' by knowing bulk and extension
Source
Francisco Suárez (Disputationes metaphysicae [1597], 40.4.16), quoted by Robert Pasnau - Metaphysical Themes 1274-1671 539
Book Reference
Pasnau,Robert: 'Metaphysical Themes 1274-1671' [OUP 2011], p.539
A Reaction
This is one step away from asking why, once we knew the bulk and extension of the thing, we would still have any interest in trying to grasp something called its 'quantity'.
Related Idea
Idea 16742 We only know essences through non-essential features, esp. those closest to the essence [Suárez]