 Locke goes on to distinguish between real essences, which are mostly hidden from us and determined by nature, and nominal essences, which we (somewhat) arbitrarily construct, but doesn’t say which he means to pick out by the expression “sortal” It is ironic that in discussion of the history of the term Locke and Aristotle are cited as the two historical sources, when a main point of Locke’s Essay was to argue against Aristotelian essentialism (see the entry on Locke).