The title of my paper may look odd. If one is questioned "What is a dog?", everyone could give a more or less valid answer. But to the question "What is not a dog?", there can be innumerable answers which may be correct, but mostly quite unhelpful. Provisionally, what I intend to do under this title is to consider what we should not hold time to be. Through the history of ideas we meet various opinions and theories concerning what time is. But it seems to me that most of them are not adequate enough, though each has its reason and often profound import as well. So I would like here to make a proposal for reconsidering how time appears in our life and thinking.