What is time? Who can easily and briefly explain this? Who can comprehend this, even in thought, so as to express it in a word? Yet what do we discuss more familiarly and knowingly in conversation than time? Surely, we understand it when we talk about it, and also understand it when we hear others talk about it. What, then, is time? If no one asks me, I know; if I want to explain it to someone who asks me, I do not know.