Full Idea
Time has parts, some of which have been, others of which are going to be, but no part of it is. The now is not a part, because a part is a measure of the whole, which must be composed of parts. Time, however, does not seem to be composed of nows.
Gist of Idea
Time has parts, but the now is not one of them, and time is not composed of nows
Source
Aristotle (Physics [c.337 BCE], 218a05), quoted by Robert Pasnau - Metaphysical Themes 1274-1671 18.1
Book Reference
Pasnau,Robert: 'Metaphysical Themes 1274-1671' [OUP 2011], p.378
A Reaction
As good an expression as you will ever find of the baffling nature of time. Only the past and the future seem substantial enough to exist. Only the now can be real, and yet it seems to be a nothing. In Phys IV.14 time is mind-dependent.
Related Idea
Idea 22956 How can time exist, when it is composed of what has ceased to be and is yet to be? [Aristotle]