Full Idea
I consider the notion of substance to be one of the keys to the true philosophy. ....I imagine that philosophers will one day know the notion of substance a bit better than they do now.
Gist of Idea
The notion of substance is one of the keys to true philosophy
Source
Gottfried Leibniz (Letters to Thomas Burnett [1703], 1699.01.20/30)
Book Reference
Leibniz,Gottfried: 'Philosophical Essays', ed/tr. Arlew,R /Garber,D [Hackett 1989], p.286
A Reaction
This is a controversial remark at this historical moment, when the apparent Aristotelian commitment to substances was becoming discredited. Personally I would eliminate substance, but not just because physicists don't refer to it.