Irreducibility of tense Earlier B-theorists argued that one could paraphrase tensed sentences (such as "the sun is now shining", uttered on September 28) into tenseless sentences (such as "on September 28, the sun shines") without loss of meaning. Later B-theorists argued that tenseless sentences could give the truth conditions of tensed sentences or their tokens.
Quentin Smith argues that "now" cannot be reduced to descriptions of dates and times, because all date and time descriptions, and therefore truth conditionals, are relative to certain events. Tensed sentences, on the other hand, do not have such truth conditionals. 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. One can think the statement "I am not uttering anything now", and such a statement would be true. The statement "I am not uttering anything simultaneous with this utterance" is self-contradictory, and cannot be true even when one thinks the statement. Finally, while tensed statements can express token-independent truth values, no token-reflexive statement can do so (by definition of the term "token-reflexive"). Smith claims that proponents of the B-theory argue that the inability to translate tensed sentences into tenseless sentences does not prove A-theory. Logician and philosopher
Arthur Prior has also drawn a distinction between what he calls A-facts and B-facts. The latter are facts about tenseless relations, such as the fact that the year 2025 is 25 years later than the year 2000. The former are tensed facts, such as that the Jurassic age is in the past, or that the end of the universe is in the future. Prior asks the reader to imagine having a headache, and after the headache subsides, saying "thank goodness that's over." Prior argues that the B-theory cannot make sense of this sentence. It seems bizarre to be thankful that a headache is earlier than one's utterance, anymore than being thankful that the headache is later than one's utterance. Indeed, most people who say "thank goodness that's over" are not even thinking of their own utterance. Therefore, when people say "thank goodness that's over," they are thankful for an A-fact, and not a B-fact. Yet, A-facts are only possible on the A-theory of time. (See also:
Further facts.)
Endurantism and perdurantism Opponents also charge the B-theory with being unable to explain persistence of objects. The two leading explanations for this phenomenon are
endurantism and
perdurantism. According to the former, an object is wholly present at every moment of its existence. According to the latter, objects are extended in time and therefore have
temporal parts. 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. An object is wholly present at a time if all of its parts co-exist at that time." Under endurantism, all objects must exist as wholes at each point in time, but an object such as a rotting fruit will have the property of being not rotten one day and being rotten on another. On eternalism, and hence the B-theory, it seems that one is committed to two conflicting states for the same object. Opponents will then charge perdurantism with numerous difficulties of its own. First, it is controversial whether perdurantism can be formulated coherently. An object is defined as a collection of spatiotemporal parts, defined as pieces of a perduring object. If objects have temporal parts, this leads to difficulties. For example, the rotating discs argument asks the reader to imagine a world containing nothing more than a homogeneous spinning disk. Under endurantism, the same disc endures despite its rotations. The perdurantist supposedly has a difficult time explaining what it means for such a disc to have a determinate state of rotation. Temporal parts also seem to act unlike physical parts. A piece of chalk can be broken into two physical halves, but it seems nonsensical to talk about breaking it into two temporal halves. American epistemologist
Roderick Chisholm argued that someone who hears the bird call "Bob White" knows "that his experience of hearing 'Bob' and his experience of hearing 'White' were not also had by two other things, each distinct from himself and from each other. The endurantist can explain the experience as "There exists an x such that x hears 'Bob' and then x hears 'White'" but the perdurantist cannot give such an account.
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.
First-person perspectives Vincent Conitzer has argued against B-theory due to the existence of first-person perspectives and Benj Hellie's
vertiginous question. He argues that arguments in favor of the A-theory of time are more effective as arguments for the combined position that A-theory is true and the "I" is metaphysically privileged from other perspectives. Caspar Hare has discussed similar ideas with the theories of
egocentric presentism and
perspectival realism. ==Notes==