Locke thought that it was impossible for there to be two things of the same kind in the same place at the same time. I offer (what looks to me like) a counterexample to that principle, involving two ships in the same place at the same time. I then consider two ways of explaining away, and one way of denying, the apparent counterexample of Locke's principle, and I argue that none is successful. I conclude that, although the case under discussion (...) does not refute Locke's principle, it constitutes a serious challenge to it. (shrink)