 It might seem as though it does not make much difference whether Aristotle subscribes to position (1) or (2). According to (2), every physical object has two forms associated with it: a matter-involving one, which combines with the proximate matter to make up the compound, and a second form or essence of this matter-involving form, which is not matter-involving. On position (1), a thing has only one form, which is “pure” in the sense that it contains no matter. However, the defender of pure forms must admit that there is also a broader definition of a thing, which does include its matter, as well as its other causes. Superficially, the only difference seems to be whether or not this “definition” gets to be classified as a form, and this might appear to be a merely verbal disagreement. In fact, more is at stake here: although, “definition”, “form” and “essence” are often treated as though they were interchangeable, a definition is strictly-speaking something linguistic, whereas an essence or form may have a structure that corresponds to something linguistic, but it is still a thing in the world. For example, the essence or form of a human being is a soul. A commitment to two essences or forms per compound substance is an additional metaphysical commitment in a way that a broader linguistic definition of a thing that mentions both its form and its matter need not be. If important theoretical work cannot be found for matter-involving forms, then, pure forms are the more ontologically parsimonious choice.