series

In philosophy, A series and B series are two different descriptions of the temporal ordering relation among events. The two series differ principally in their use of tense to describe the temporal relation between events. The terms were introduced by the Scottish idealist philosopher John McTaggart in 1908 as part of his argument for the unreality of time, but since then they have become widely used terms of reference in modern discussions of the philosophy of time.
Metaphysical issues that divide theorists concern the reality of the past, the reality of the future, and the ontological status of the present.

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