Reprinted from ‘Dialogue’ (Canadian Philosophical Review), vol. , 1962, by permission of the editors

St Augustine said, ‘When you do not ask me what Time is, I know perfectly well; but when you do ask me, I cannot think what to say.’ What, then, was it that he knew perfectly well, and what was it that he did not know? Obviously he knew perfectly well such things as these, that what happened yesterday is more recent than what happened a month ago; that a traveller who walks four miles in an hour goes twice as fast as a traveller who takes two hours over the same journey. He knew how to say things and how to understand things said to him which specified dates, durations and times of day; epochs, seasons and moments. He knew when it was midday and he could use the calendar. He could cope efficiently and easily with concrete chronological and chronometrical tasks. He could use and understand tensed verbs. What he could not do is to give any reply at all to such abstract questions as these: what is it that there is twice as much of in a fortnight as in a week? Why could Time, unlike a battle, never have started, and why can Time, unlike a concert, never come to a stop? Does Time flow on at an uniform or an irregular speed, and, in either case, is its speed measured in a second sort of Time? In short, what is Time-is it a Thing or a Process or a Relation? Is it a sort of cosmic river, only one without any tangible water between its nonexisting banks? One which flows out of no spring and pours out into no ocean?