sentences:  McTaggart in "The Unreality of Time" identified two descriptions of time, which he called the A-series and the B-series.The A-series identifies positions in time as past, present, or future, and thus assumes that the "present" has some objective reality, as in both presentism and the growing block universe.The B-series defines a given event as earlier or later than another event, but does not assume an objective present, as in four-dimensionalism.