 By introducing the distinction between real and nominal essences and thereby dividing their roles, Locke has provided himself with a number of resources to criticize the Scholastic theory of species. There are, however, reasons to worry about the viability of these criticisms. After all, these arguments seem to beg the question against the Aristotelian tradition. The existence of substantial forms need not entail the existence of hard-edged natural kinds, and so Locke's 'moulds and forms' metaphor does not damage the Aristotelian position. In the borderline cases argument, the Aristotelian tradition can appeal to their matter/form distinction and remind Locke that even though the form guides the changes in material substances, not all matter is suitable for all changes. That is, a form is teleological and is what guides the matter as it achieves its final cause, but not all matter is suitable to achieve that end. For example, wood might be highly suitable to construct a ship, but stone would not be. The matter, if suitable, may indeed achieve the end of the formal cause, however, when the matter is not suitable it can result in monsters and deformities. With regard to abstract ideas, i.e., nominal essences, being the foundation of species, the Aristotelian tradition can surely reject the claim that the form plays no role in the formation of our abstract ideas. So long as our abstract ideas must be answerable to what exists in nature, and so long as nature presents us with the effects of the substantial form, what we have available to include in our nominal essences will be very much rooted in the substantial form. This same argument can be applied to the third criticism as well; substantial forms guide our selection of nominally essential properties because they carve nature at its joints and help some appear more natural than others. Finally, the claim that generality does not exist in nature is question-begging: if there are substantial forms, then there is generality in nature.