E.J. Lowe on the Unity Problem

Some properties are connected in a perspicuous and unproblematic way. For instance, the possession of shape clearly entails the possession of size (and vice versa). In other cases the connection is not so perspicuous. For instance, assuming that the precise rest mass and negative charge of an electron are both among its fundamental intrinsic properties, what links them, given that those properties are inherently separable? (Their separability is apparent from the fact that other kinds of particle have the same mass as an electron but a different charge, or the same charge but a different mass.) Given the inherent separability of those properties, what explains their conjunction in this case? Oderberg (2007, 2011) calls this the "unity problem", and attempts to solve it have issued from assorted schools of thought within both substance ontology and the metaphysics of natural kinds. One of the more significant of these solutions is proffered by E.J. Lowe as part of his four-category ontology. Here I explicate his solution, raise a possible objection, and suggest a reply.