In one sense, everyone knows what the present is, and tends to understand by it what psychologists call "the specious present" and everyone who speaks a natural language knows some terminology and and grammatical and logical rules for them that express time and tense; in another sense it is difficult to define clearly, and comes with problems.

One problem is when it is now - yes, now: but also one millionth of one millionth of a second ago, or not? - and whether time is infinitely divisible, and what are the differences between a physical sense of "now" and a psychological sense of the same.