But the two times, past and future, how can they be, since the past is no more and the future is not yet? On the other hand, if the present were always present and never flowed away into the past, it would not be time at all, but eternity. But if the present is only time, because it flows away into the past, how can we say that it is? For it is, only because it will cease to be.

St. Augustine, quoted in Giorgio Agamben, Infancy and History (Verso, 2007) p. 104