 The answer is correct, but it carries the counter-intuitive implication that motion is not something that happens at any instant, but rather only over finite periods of time. Think about it this way: time, as we said, is composed only of instants. No distance is traveled during any instant. So when does the arrow actually move? How does it get from one place to another at a later moment? There’s only one answer: the arrow gets from point \(X\) at time 1 to point \(Y\) at time 2 simply in virtue of being at successive intermediate points at successive intermediate times—the arrow never changes its position during an instant but only over intervals composed of instants, by the occupation of different positions at different times. In Bergson’s memorable words—which he thought expressed an absurdity—‘movement is composed of immobilities’ (1911, 308): getting from \(X\) to \(Y\) is a matter of occupying exactly one place in between at each instant (in the right order of course). For further discussion of this ‘at-at’ conception of time see Arntzenius (2000) and Salmon (2001, 23-4).