Full Idea
The active principle is not attributed by me to bare or primary matter, which is merely passive ...but to clothed or secondary matter which in addition contains a primitive entelechy, or active principle.
Clarification
An 'entelechy' makes potentialities become actual
Gist of Idea
Bare or primary matter is passive; it is clothed or secondary matter which contains action
Source
Gottfried Leibniz (Letters to Wagner [1710], 1710 §2)
Book Reference
Leibniz,Gottfried: 'Leibniz Selections', ed/tr. Wiener,Philip P. [Scribners 1951], p.504
A Reaction
Secondary matter contains monads. The puzzling question is what primary matter consists of. It is not atoms, because it is infinitely divisible, and it seems to be composed of corpuscles. But what is it made of? Just gunge? He says it is 'flux'.