When matter is unsuitable to achieve the end of the formal cause, the result can be monsters and deformities rather than a counterexample to the existence of substantial forms

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' metaph