Full Idea
By 'substance', in the context of the mind, we mean a persisting object or thing which can undergo changes in its properties over time while remaining one and the same thing.
Gist of Idea
A 'substance' is a thing that remains the same when its properties change
Source
E.J. Lowe (Introduction to the Philosophy of Mind [2000], Ch. 2)
Book Reference
Lowe,E.J.: 'Introduction to the Philosophy of Mind' [CUP 2000], p.13
A Reaction
A neat account of the traditional philosophical notion of a substance. It invites the obvious question of how you know that a thing is the same if all of its properties seem to have changed (as with Descartes' wax). Epistemology discredits ontology.