Whatever cannot be imagined apart from a thing is a determinable or mode of that thing, not an independently existing substance.

This sort of abstraction Norris calls “modal abstraction.” Since we cannot imagine a body without some shape and some dimensions, shape and dimensions are determinables, or modes, of extension. Shape is not an independently existing thing, but is always a modification of an independently existing thing. Since Norris holds that our clear and distinct mental propositions track ideal propositions, we can conclude that shape and dimensions are not substances, but modes. Modal abstraction turns out t