Full Idea
I maintain that substances, whether material or immaterial, cannot be conceived in their bare essence without any activity, activity being of the essence of substance in general.
Gist of Idea
Material or immaterial substances cannot be conceived without their essential activity
Source
Gottfried Leibniz (New Essays on Human Understanding [1704], Pref)
Book Reference
Leibniz,Gottfried: 'Philosophical Writings', ed/tr. Parkinson,G.H.R. [Dent 1973], p.168
A Reaction
Thus there could be no 'tabula rasa', because that would be an inactive mental substance. This strikes me as a nice question for modern physicists. Do they regard movement as essential, or an addition to bare particles? I'm with Leibniz. Essentialism.