 It is likely that Locke was aware of the limits of these criticisms, after all, he was both educated with and taught Scholastic texts. Nevertheless, as Jolley argues (1999, 146), Locke could reply by arguing that the properties of bodies are causally dependent on their essences, just as all the properties of every triangle flow from the essences of the triangles, but then why do mathematical and geometrical essences produce hard-edged kinds while the essences of material bodies do not? More to the point, if substantial forms are causal and explanatory posits in Aristotelian scientia, and they are held to be knowable via perception, but the evidence from perception yields a host of borderline cases, then it is plausible to conclude that either substantial forms are not doing their job or there are no such forms. However, this reply will not cut much ice with the Aristotelians, who have yet to be shown why their appeal to the weakness of matter is insufficient to explain generative variation.