Spatio-temporal coincidence and the grounding problem

A lot of people believe that distinct objects can occupy precisely the same place for the entire time during which they exist. Such people have to provide an answer to the 'grounding problem' – they have to explain how such things, alike in so many ways, nonetheless manage to fall under different sortals, or have different modal properties. I argue in detail that they cannot say that there is anything in virtue of which spatio-temporally coincident things have those properties. However, I also argue that this may not be as bad as it looks, and that there is a way to make sense of the claim that such properties are primitive.