Michael Jacovides

Seth Pringle-Pattison (233n1) observed that Locke “teaches a twofold mystery—in the first place, of the essence (‘for the powers or qualities that are observable by us are not the real essence of that substance, but depend upon it or flow from it’), and in the second place, of the substance itself (‘Besides, a man has no idea of substance in general, nor knows what substance is in itself.’ Bk. II.31.13).” In this paper, I’ll explain the relation between the two mysteries. Our Rosetta Stone is Locke’s argument that we understand body and spirit equally well since we are ignorant of their underlying substances but we “have distinct clear Ideas of two primary Qualities, or Properties” (2.23.30) of each. I’ll show that he is working with a restricted notion of primary quality in this passage, but one that demonstrably falls under the kind defined in his chapter on primary and secondary qualities. According to Locke, the fundamental primary qualities of bodies flow from corporeal substances and the determinations of these fundamental qualities constitute real essences. Locke’s discussion can’t be understood without understanding the relevant scholastic background. In the first half of my paper, I’ll explain his argument as an idiosyncratic application of doctrines he learned and taught at Oxford. In the second half, I’ll use lessons from my interpretation of the argument to explain the relation that Locke believes obtains between a substance and its fundamental primary qualities, and then I’ll build upon that explanation to elucidate his general account (insofar as he has a general account) of the inherence of qualities in corporeal substances

Locke’s porphyry argument at 2.8.19 of the Essay has not been properly appreciated. On my reconstruction, Locke argues from the premise that porphyry undergoes a mere Cambridge change of color in different lighting conditions to the conclusion that porphyry’s colors do not belong to it as it is in itself. I argue that his argument is not quite sound, but it would be if Locke chose a different stone, alexandrite. Examining his argument teaches us something about the relation between explanatory qualities and real alterations and something about the ways that colors inhere in bodies