J.M.E. McTaggart

British idealist philosopher who made the most influential contribution to the philosophy of time: the distinction between the A-series (past/present/future) and B-series (earlier/later-than), and the argument that time is ultimately unreal.

A-series / B-series distinction: the most basic distinction in the metaphysics of time. The A-series is tensed (past, present, future); the B-series is tenseless (earlier-than, simultaneous-with, later-than). Argument for the unreality of time: the A-series is essential to time (change requires tense) but also paradoxical (every event is past, present, and future), so time is unreal. The Nature of Existence: systematic idealist metaphysics.