  Confusion and disagreement around the notion of time is due to the fact that
we often fail to recognize that we call 'time' a variety of distinct notions,
only partially related to one another. Many apparently obvious properties of
time are results of different kinds of approximations, idealizations, or
special contexts. I illustrate a number of distinct notions of time, their
differences and relations; they are all relevant for describing the real world.
To understand time, we have to break it apart.
