  Thinking first of time and its various puzzles, or aporiai, we saw that Aristotle poses a simple question: does time exist?  He answers this question in the affirmative, but only because in the end he treats it as a categorically circumscribed question.   He claims that ‘time is the measure of motion with respect to the before and after’ (Phys. 219b1–2).   By offering this definition, Aristotle is able to advance the judgment that time does exist, because it is an entity in the category of quantity: time is to motion or change as length is to a line.  Time thus exists, but like all items in any non-substance category, it exists in a dependent sort of way. Just as if there were no lines there would be no length, so if there were no change there would be no time. Now, this feature of Aristotle’s theory of time has occasioned both critical and favorable  reactions.[16]   In the present context, however, it is important only that it serves to demonstrate how Aristotle handles questions of existence: they are, at root, questions about category membership. A question as to whether, e.g., universals or places or relations exist, is ultimately, for Aristotle, also a question concerning their category of being, if any.