Full Idea
By substance we can understand nothing else than a thing which so exists that it needs no other thing in order to exist.
Gist of Idea
A substance needs nothing else in order to exist
Source
René Descartes (Principles of Philosophy [1646], I.51)
Book Reference
Descartes,René: 'Philosophical Essays and Correspondence', ed/tr. Ariew,Roger [Hackett 2000], p.244
A Reaction
Properties, of course, are the things which have dependent existence. Can properties be reduced to substances (e.g. by adopting a materialist theory of mind)? Note that Descartes does not think that substances depend on God for existence.