What is the relation between time and change? Does time depend on the mind? Is the present always the same or is it always different? Aristotle tackles these questions in the Physics, and Time for Aristotle is the first book in English devoted to this discussion. Aristotle claims that time is not a kind of change, but that it is something dependent on change; he defines it as a kind of “number of change.” Ursula Coope argues that what this means is that time is a kind of order (not, as is commonly supposed, a kind of measure). It is universal order within which all changes are related to each other. This interpretation enables Coope to explain two puzzling claims that Aristotle makes: that the now is like a moving thing, and that time depends for its existence on the mind. Brilliantly lucid in its explanation of this challenging section of the Physics, Time for Aristotle shows his discussion to be of enduring philosophical interest.