If one googles “ontology” and “substance” we come up with
“about 1,970,000 results (0.16 seconds)”
google.com/search?q=ontology+substancd+defintion&oq=ontology+substancd+defintion&aqs=chrome.0.69i57j0.9907j0&sourceid=chrome&ie=UTF-8#q=ontology+substance+definition&spell=1&sa=X&ei=UZnmUcGROsHXyAGSjYCYAw&ved=0CCsQvwUoAA&bav=on.2,or.r_cp.r_qf.&bvm=bv.49405654%2Cd.aWc%2Cpv.xjs.s.en_US.QXiTEk6XjhM.O&fp=2a397225d5c65770&biw=1366&bih=667
IOW: Over a million references.
And I took the first hit and copied the first sentence:
“Substance is a key concept in ontology”
And here’s something from the Stanford Dictionary of Philosophy (bold and font increase mine)
- Ontological dependence, substance, and properties
A crucial notion in metaphysics is that of one entity depending for its existence upon another entity—not in a merely causal sense, but in a deeper, ontological sense. The kind of dependence in question must also be distinguished from any kind of logical dependence, because logical relations, strictly speaking, can obtain only between propositions, not between concrete objects, nor between abstract objects that are not propositional in nature. Thus, a substance is often conceived to be an object that does not depend for its existence upon anything else. (For example, Descartes asserts that ‘by substance we can understand nothing other than a thing which exists in such a way as to depend on no other thing for its existence’ (Writings, vol. I, p. 210).) Again, properties are often said to depend for their existence upon the objects that possess them. (Thus, Descartes also remarks that ‘we know by the natural light that a real attribute cannot belong to nothing’ (Writings, vol. II, p. 114).) So how should this relationship of existential dependence be defined? An obvious proposal would be to say, quite simply:
(EDR) x dependsR for its existence upon y =df Necessarily, x exists only if y exists.