On the one hand they can be characterized as past, present or future, normally indicated in natural languages such as English by the verbal inflection of tenses or auxiliary adverbial modifiers.
Philosophers are divided as to whether the tensed or tenseless mode of expressing temporal fact is fundamental.
[4] Some philosophers have criticised hybrid theories, where one holds a tenseless view of time but asserts that the present has special properties, as falling foul of McTaggart's paradox.
[6] The debate between A-theorists and B-theorists is a continuation of a metaphysical dispute reaching back to the ancient Greek philosophers Heraclitus and Parmenides.
[13][6] B-theorists such as D. H. Mellor[14] and J. J. C. Smart[15] wish to eliminate all talk of past, present and future in favour of a tenseless ordering of events, believing the past, present, and future to be equally real, opposing the idea that they are irreducible foundations of temporality.
[21] The B-theorist could argue that "now" is reducible to a token-reflexive phrase such as "simultaneous with this utterance", yet Smith states that even such an argument fails to eliminate tense.
[24] Logician and philosopher Arthur Prior has also drawn a distinction between what he calls A-facts and B-facts.
[26][27] Hales and Johnson explain endurantism as follows: "something is an enduring object only if it is wholly present at each time in which it exists.
[26] The spacetime (Minkowskian) interpretation of relativity adds an additional problem for endurantism under B-theory.
For example, the rotating discs argument asks the reader to imagine a world containing nothing more than a homogeneous spinning disk.
The perdurantist supposedly has a difficult time explaining what it means for such a disc to have a determinate state of rotation.
[32] Peter van Inwagen asks the reader to consider Descartes as a four-dimensional object that extends from 1596 to 1650.
If Descartes had lived a much shorter life, he would have had a radically different set of temporal parts.
This diminished Descartes, he argues, could not have been the same person on perdurantism, since their temporal extents and parts are so different.