Full Idea
Everything accidental or changeable ought to be a modification of something essential or perpetual.
Gist of Idea
Changeable accidents are modifications of unchanging essences
Source
Gottfried Leibniz (Letters to Burcher De Volder [1706], 1704.06.30)
Book Reference
Leibniz,Gottfried: 'Philosophical Essays', ed/tr. Arlew,R /Garber,D [Hackett 1989], p.180
A Reaction
Clear evidence that Leibniz is very much a traditional Aristotelian essentialist, and not as modal logicians tend to characterise him, as a super-essentialist who thinks all properties are essential. They are necessary for identity, but that's different.