A Series and B Series (by J.M.E. McTaggart)

J.M.E. McTaggart's A Series and B Series are ways to understand time. The B Series frames time as a fixed, unchanging timeline—events are either past, present, or future, but their position doesn’t change. The A Series, however, sees time as fluid; events are constantly moving from future to present to past. Think of the B Series as a stationary timeline, and the A Series as the dynamic experience of time passing. McTaggart argued that only the A Series captures the true nature of time, emphasizing its flowing, changeable quality.