Full Idea
Since everything that one conceives in substances reduces to their actions and passions and to the dispositions that they have for this effect, I don't see how one can find there anything more primitive than the principle of all of this, which is force.
Gist of Idea
The most primitive thing in substances is force, which leads to their actions and dispositions
Source
Gottfried Leibniz (Letters to Jacques Lenfant [1693], 1693.11.25), quoted by Daniel Garber - Leibniz:Body,Substance,Monad 4
Book Reference
Garber,Daniel: 'Leibniz: Body, Substance, Monad' [OUP 2009], p.171
A Reaction
This is an attempt to connect Aristotelian essentialism with the notion of force in the new physics, and strikes me as an improvement on the original, and as good a basis for metaphysics as any I have heard of.
Related Ideas
Idea 12714 The substantial form is the principle of action or the primitive force of acting [Leibniz]
Idea 13095 Essence is primitive force, or a law of change [Leibniz]
Idea 13193 Active force is not just potential for action, since it involves a real effort or striving [Leibniz]