According to Aristotle, time is the number of change with respect to before (proteron) and after (hysteron). This can sound odd to our ears, because we often tend to think of time as our paradigmatic case of before-and-after, and therefore it could sound to us like he's simply saying that time is the number of change that has to do with time.
But it's interesting that Aristotle does not think time is the paradigmatic case of before-and-after; he is very clear that the most obvious case of before-and-after is place or relative position. This is one reason Aristotle seems to give change of place an especially important role for understanding time: it gives us a clear way to think of the numbers we give to time as having a before-and-after, by giving us a change that has a clear link with relative position and its before-and-after; and since time is a numeration of change, it inherits the before-and-after relation. The before-and-after of time is primarily reached by mapping, in a change, time to place, where the latter is conceived in a way relative to a particular reference point. As he says at one point, the change goes with the distance and the time with the change.
Thus on this view (1) time is not the most basic form of before-and-after ordering, but a derivative one; (2) it is not even the form of before-and-after ordering that we know first; and (3) it is not even the form of before-and-after ordering that we know best.
