MA Thesis Defense: Jason Rosencrantz

‘Locke on substance kinds and human minds’
Jason Rosencrantz (Cal State Long Beach)
24 Mar 2026 •  11:30am–1:30pm  •  MHB–915

Abstract: Locke was explicitly agnostic about the substantial basis of human minds, and famously claimed that there was no contradiction in it that God should have given matter fitly disposed some degree of thought. This ‘thinking matter’ hypothesis, insofar as it admits of degrees of mentality that can accommodate non-human animal minds, stands in sharp contrast to the stark Cartesian dualism according to which human animals are possessed of immaterial minds and all non-human animals are mindless material machines. For Locke, Descartes’ metaphysical division between the substantial basis of human beings and all other animals runs counter to the manifest continuity among species one encounters in nature, a continuity that Locke supposed runs by gentle degrees up a hierarchy of perfection from senseless matter to an eternal omnipotent being that cannot be matter.
     Despite Locke’s explicit agnosticism, many scholars have wondered just where along this continuous hierarchy Locke would locate an ontological jump from a material to an immaterial substance, and have interpreted him as implicitly inclined to judge it more probable either that human minds are material or that human minds are immaterial. Jolley and Downing, for example, both argue that Locke is best read as an implicit-materialist about human minds: Jolley argues by elimination from an array of metaphysical possibilities and Downing argues from continuity with the minds of beasts. By contrast, Duncan and Rickless both argue that Locke is best read as an implicit-immaterialist about human minds: Rickless argues from Locke’s comments on the relative speed of mental operations and Duncan argues from continuity with God’s mind.
     Taking inspiration from Kim’s reading of Locke as a ‘consistent nominalist’ who applied a nominal essence thesis not only to ordinary substance kinds such as gold and horse, but also to the more general substance kinds such as mind and matter, I aim to show that Locke’s substance nominalism runs deeper than any of his apparent metaphysical inclinations. I argue that Locke’s fundamental ontological and idea-theoretical commitments motivate a principled neutrality regarding the substantial basis of things we categorize as ‘thinking’ or as ‘material’.
     According to Locke, the sortal terms ‘mind’ and ‘matter’, which figure so prominently in the competing propositions that human minds are material or that human minds are immaterial, stand for complex ideas of substance kinds. But such ideas, on Locke’s analysis, are strictly limited in their aptitude to positively bear certain representational values: they are always to some degree obscure, always inadequate to the task of perfectly representing their archetypes, and always false when tacitly supposed to conform to the real essence of any sort of really existing being. I evaluate the competing arguments for Locke’s metaphysical inclinations in light of the strict representational limits and capacities that Locke’s genetic theory imposes on complex ideas of substances, and argue that all four arguments are premised on a conflation between real and nominal essences.

Oral defenses are open to the public.

For a draft copy of the thesis in advance, please contact Jason <jason.rosencrantz01@student.csulb.edu> directly.