Since one of my complaints will be that I find it difficult to give a meaning to the position that I am attacking, it would perhaps be unfair for me to try to summarize it. I will therefore let William Lane Craig, who advocates the view, explain it:
Sharp-sighted critics of McTaggart...have insisted almost from the beginning that a dynamic or tensed theory of time implies a commitment to presentism, the doctrine that the only temporal entities that exist are present entities. According to presentism, past and future entities do not exist. Thus, there really are no past or future events, except in the sense that there have been certain events and there will be certain others; the only real events are present events...Temporal becoming is not the exchange of tense on the part of tenselessly existing events but the coming into and going out of existence of the entities themselves. (Time and Eternity, p. 148)For reasons that mostly elude me, quite a few great Christian philosophy graduate students I hang out with (cheers, gentlemen!), both in person and on-line, find this position in the philosophy of time intuitively plausible. I find it utterly unattractive--in fact, almost self-evidently false. But it would be more useful for me to spell out some of the problems that occur to me. I make no claim that this is an exhaustive list. In fact, one reason I'm writing this post is because more kept occurring to me, and I didn't want to clutter the paper with too many endnotes mentioning them.
The first question I have about this position is simply: What does it mean? Let me be clear. I have some idea of what people mean (they are sometimes called "openists" or "open futurists") who say that future entities do not exist. What they mean is that statements about the future have no truth value. The statement that it will rain tomorrow, or even a tenseless version of this ("It [tenselessly] rains on April 11, 2014") simply is neither true nor false when uttered before April 11, 2014. Often one motive for openism is related to human freedom, the idea being that it blocks human free will if statements about what I will do tomorrow are already true today. However, I've never heard of an openist about the past! On the contrary, the whole concern regarding freedom is to make the future unlike the past, to assert a strong asymmetry between them; the past, on openism, is fixed and unchangeable, but the future is still unmade.
But that can't be what the presentist means, and especially not what Craig means, by saying that past and future entities do not exist. The presentist is asserting that both past and future entities are strictly non-existent. On this point, he is asserting a symmetry rather than an asymmetry between the past and the future. Moreover, Craig isn't an openist! He has written at length against open theism, the position in the philosophy of religion that goes hand in hand with openism in the philosophy of time and that postulates limitations on the concept of divine foreknowledge.
Craig clearly believes that statements about the past and the future are true. But if the tenseless proposition "Socrates exists in 405 B.C." is true, then what does it mean to say that Socrates doesn't exist in any sense? Can we not say that Socrates exists just in the sense that to assert his existence relative to 405 B.C. is to make a true statement? Similarly, to assert my existence relative to A.D. 2014 is also to make a true statement. Thus we can explain a fairly simple and straightforward sense in which both Socrates and I exist in the grand scheme of things, each of us existing relative to particular points in time. We can explain this in terms of the truth of propositions about the existence of me and Socrates.
At this point I can hear all the frustrated temporal A theorists jumping up and down and telling me why there has to be a Real Now and why the B theory of time, which denies the existence of an objective and Real Now, must be wrong.
But just at this point in the post I am objecting to presentism, not to all A theories of time. (I'll get later to some considerations that tell against all A theories of time.) According to the B theory of time (to give a wildly and irresponsibly brief version), all points in time have an equal claim to be "now," except relative to the experiences of conscious beings. There is no objective or Real Now that lies in 2014 rather than in 405 B.C. Relative to some of Lydia's conscious experiences, 2014 is now. Relative to some of Socrates' conscious experiences, 405 B.C. can be thought of as now, but neither of these perspectives is "more right" than the other. There is no Real Now that has kept moving and has now "gotten" to 2014. But I am asking what presentism means, specifically. I am asking about presentism as opposed not only to the B theory of time but also as opposed to what is known as a "growing block" view, according to which past entities and events are real but future ones are not. Or an "illuminated present" view according to which past and future events are real but only one slice of time is "now." Both of these, along with presentism, have a Real Now, but not all of them are presentism. What does presentism mean, especially in denying the existence of past entities?
There is one way that I can think of to give presentism meaning, but it involves paying a pretty steep price, and it is not a position that Craig argues for anywhere that I have seen: One could deny that there are any tenseless propositions. All A theorists are committed to arguing that there are irreducible tensed facts, such as "It is now 3 p.m." I disagree with them, and I discuss how a B theorist can reduce such facts to tenseless truths in the paper. But my point here is this: While an A theorist like Craig will argue, and Craig does argue, that there are irreducible tensed facts, it is a much stronger position that there are no tenseless facts. Craig argues that a proposition like "The meeting is [tenseless] at 3 p.m. on April 14, 2014" does not fully give the content of a belief like, "The meeting is now" or "The meeting is today." But he never denies the possibility of tenseless propositions. If he did do so, this could give "cash value" to his denial of the existence of any past or future entities. In that case, "Socrates exists in 405 B.C." would simply be false if uttered now, because it is not now 405 B.C. and because there literally is no way to use verbs tenselessly.
Such a view would not be ipso facto openist, because one could still say that "I will mow the lawn tomorrow" has a truth value. But such a view would deny that there is any tenseless proposition, "Lydia mows the lawn on April 12, 2014" that is true or false. Everything has to be tensed.
Tenseless propositions are pretty standard fare for philosophers. They explain the way in which two people at different times, or the same person at different times, can believe the same content. There is some sense in which, if my historical beliefs are correct, I believe the same thing about Napoleon's losing the Battle of Waterloo as someone living twenty-five years ago or even someone living at the time of the battle. It is generally considered quite useful, philosophically, to be able to translate "Napoleon lost the Battle of Waterloo in 1815" into a tenseless proposition that can be the same proposition and be believed at different times. I think it would be a big mistake for presentists to reject tenseless propositions just in order to give their presentism meaning. It would be better for them to cease to be presentists and become, at least, growing block theorists. (I am not denying that growing block theories can be criticized as well--from both the presentist perspective and the B theory perspective.)
Craig would have even more difficulty accepting into his system the view that there are no tenseless propositions, or that tenseless propositions are meaningless, or anything of that kind, because he holds that God is "outside of time sans creation." So what would God know sans creation? Presumably, for God to be omniscient about Napoleon at the "stage" (for want of a better word) of God's life in which God "was" (for want of a better word) not in time, God would have to know tenseless facts about Napoleon and the Battle of Waterloo. So a further epicycle would have to be added to the effect that tenseless propositions became meaningless at the first moment of creation.
I doubt that this is a direction that most presentists will want to go, and I stress again that Craig never attacks tenseless propositions uberhaupt. I bring it up only as a possible way to give meaning to the presentist's denial of existence to past and future entities and events.
Consider, too, the fact that what Craig is saying in advocating presentism gives the distinct impression that past entities are unreal. After all, he says that they don't exist, apparently not in any sense at all. But past entities, including ourselves at past moments, leave causal traces. The "me" of an hour ago must have some place in the schema of reality, taken as a whole, because there are bar cookies sitting on the counter right now that were made by the "me" of an hour ago! To say that the past is strictly unreal makes no sense of the causal relationship between present entities and past entities.
Another consideration: Craig alleges that there are special theological problems with the B theory of time. One of the most common of these, and the kind of thing that seems to resonate with those influenced by Craig's view, is the "Jesus is still on the cross" accusation. Craig says that, on a B theory of time, God can never be victorious over sin, because the B theorist refuses to postulate a Real Now and the strict and absolute nonexistence of past entities and events. Craig says that it follows from this that "Christ hangs permanently on the cross" on a B theory of time and God never triumphs over evil. (Time and Eternity, p. 214)
First of all, this is not true, because the word "still" is a tensed term as is the word "permanently." The B theorist can give a perfectly good account of the sense in which Jesus is not still on the cross now, which is to say, simultaneous with Lydia's existence in history, with Lydia's mental experience, and with April 11, 2014. Once we are dealing with tensed terms like "still" and "permanently," the B theorist has no problem explaining that some events have already happened on the B series line and are over prior to such-and-such a moment (which is the moment of a certain experience of mine) on the B timeline, the moment at which I am speaking. So, no, Jesus is not still on the cross.
Beyond that, if we are just going to try to use ordinary language and toss around alleged theological problems, two can play at that game: If there is no timeless truth that Jesus dies, tenseless, on the cross for our sins, how does God save us? If the past is nonexistent, then Jesus' death on the cross is nonexistent. So on what basis are our sins forgiven?
And then there's that pesky verse (Revelation 13:8) about the "Lamb slain from the foundation of the world." To put it mildly, such a statement is far more consonant with a view on which there really are tenseless truths that are always true and that these include truths about Jesus' death.
Probably it would be better for neither side to try to allege such theological problems, though I think the biblical reference to Revelation 13:8 is a prima facie conundrum for either the presentist or the openist. In general, though, it would be better for the presentist to acknowledge that the B theorist does not hold that "Jesus is permanently on the cross" or that "I am both five years old and my present age forever" or anything else of the kind, and for the B theorist to grant that the presentist can have God forgiving us on the grounds that Jesus did die for our sins, even though the past is, according to the presentist, nonexistent. My point here is that, once we get going, there are as many things that the B theorist can say with some plausibility about alleged "theological problems" with presentism as vice versa.
One other point about the "Jesus is still on the cross" allegation, or, as one philosophy student put it to me, criticizing the B theory, "According to your view, I'm still five years old": In bringing that criticism, the presentist attacks the growing block theorist and the illuminated block theorist as well as the B theorist. This is because, even though both of those theories do hold that there is an absolute Now, they do not say, like the presentist, that the past is strictly and absolutely non-existent. Hence, perhaps the presentist should ask other A theorists why they don't think that "Jesus is still on the cross," since they do hold that the past is part of reality.
More problems for presentism: This one is a problem for all A theories, including openism. All theories with an Absolute Now are forced to take a view of the meaning of physics and relativity theory that is anti-Einsteinian. If you have one Absolute Now, you must deny relativity theory as usually construed and hold that there is absolute time which yields a preferred frame of reference. Now, I'm not going to press this as an insuperable problem. I myself am a realist in the face of quantum mechanics and hence deny the standard interpretation of quantum mechanics as meaning that reality is merely probabilistic at bottom, so I'm in no position to throw stones about non-standard metaphysical interpretations of physics. But is it really a bullet that the A theorist or openist wants to bite to say that there is one absolute, preferred, inertial frame of reference?
Craig does bite this bullet. He has quite a few pages on the subject. He actually accepts that measuring instruments extend and contract in the direction of motion relative to the absolute frame of reference. (Time and Eternity, p. 54.) Craig implies repeatedly that the only reason for rejecting this Lorenzian perspective is verificationism, because the Lorenz solution is empirically equivalent to the Einsteinian interpretation. But it is by no means true in the philosophy of science that only verificationism can lead us to prefer what seems to be the simpler explanation to save the phenomena! Whether the long-standing interpretation of relativity theory as meaning that there is no preferred space-time frame of reference is indeed simpler than the idea that measuring instruments lengthen and contract relative to a preferred frame of reference is not a question on which I am going to make dogmatic pronouncements. I merely point out that saying "verificationism" does not settle the matter. Indeed, if scientists always got stuck as between empirically equivalent theories, science could not proceed at all. The use of simplicity considerations, leading a scientist to accept only such entities as he has empirical evidence for, should not be taken to be equivalent to verificationist philosophy.
Another drawback both to presentism and to the growing block view is that they unreasonably limit our options in responding to the problem of induction by limiting reality either to the present only or to the past and present only. Readers will find my husband's and my response to the problem of induction in Chapter 7 of our book on metaepistemology. The connection to the philosophy of time, briefly, is this: We can apply certain mathematical theorems about sampling and representativeness to solve the problem of induction, but only if we take ourselves to be sampling out of a set of entities with particular statistical properties. So, for example, if I have eaten watermelon many times and found it sweet, this can be rationally connected to the proposition that the next piece of watermelon I eat will be sweet. But the connection runs through a proposition about the proportion of sweet watermelons to all the watermelons. This set should be thought of as existing not only across space but also across time. In fact, if this set could not include either past or future entities, the whole notion of sampling from a set (of watermelons) as part of making a rational induction about what will happen in the future based on the past becomes meaningless. Even if we restrict the set just to "watermelons sold at such-and-such a store" rather than all watermelons throughout the history of the universe, the set still must include both past and future watermelons, or else I cannot relate watermelons I have eaten in the past to the watermelon I will eat tomorrow. The B theory, which denies that reality literally "grows" as a Real Now moves along, has no problem at all with the idea of sampling reality across time. The B theorist takes me to be sampling from a set of watermelons that are part of reality taken as a whole, and this includes both past and future watermelons. As seen above, this does not mean that watermelons that will grow in 2015 "exist now," simultaneous on the timeline with April, 2014. They are 2015 watermelons. But the B theory denies that either the past or the future (or both, per presentism) are literally not part of reality in any sense whatsoever. The presentist position would seem to mean that past and future watermelons cannot in any sense be thought of as part of the same set which I am sampling when I eat a watermelon.
Last but not least, I want to hit what seems to me a gigantic problem for presentism: What is the duration of the Real Now? It should be clear right away that this question is a vital one for the presentist, because his entire ontology depends on the present moment. The presentist's entire theory of time depends on the insistence that there really is a Real Now. And only what exists in that present moment is real at all!
Craig admits quite candidly that this is a difficult issue for presentism. He considers and rejects two views: First, he rejects the view that the present moment has zero measure, that it is durationless. He points out that it seems quite impossible to "make up" temporal duration out of strictly durationless moments--the temporal equivalent of geometric points (which take up no space). And on presentism, that is exactly what the present moment has to do: The Now has to be the constituent entity from which all of time is made, because only what is real in the present is real at all. Second, he rejects the view that time can be quantized into smallest possible units--temporal atoms known in the philosophy of time as chronons. Craig explains that the chronon view has hugely problematic consequences. One such consequence would be that motion itself would be discontinuous! The idea that things move in a smooth and continuous fashion through space would have to be an illusion. Everything would have to jump. Your blood would jump jerkily through your veins, cars would really be jumping down the road in discontinuous spatial frames. Here, too (though Craig does not bring it up), I want to mention that the chronon idea would seem to revive the famous Zeno's paradox that it is impossible ever to cross a room. The solution to that paradox depends on there being no smallest unit of time. So Craig rightly rejects the idea that the Real Now has a duration of a single smallest "time atom." But what is left? Any larger, technically divisible, unit of time chosen for the Real Now would be chosen arbitrarily. Why make it a second when it could be a half-second?
What Craig decides, in the face of these difficulties, is that the duration of the present moment is not an objective matter but is relative to the universe of discourse!
On this view, to ask, "What is the extent of the present?" is a malformed question. In order for the question to be meaningful, one must stipulate what it is we are talking about: the present vibration of an atomic clock, the present session of Congress, the present war, or what have you? There is no such metric interval as "the present," period; we must speak of "the present _____," where the blank is filled by a reference to some event or thing....Such a view is admittedly strange because it implies that there is no such thing as the present time. Rather what is present depends on the the universe of discourse: Are we talking about seconds, or minutes, or hours, or what? (Time and Eternity, pp. 159-160)This easy-going view of the meaning of "the present" would be all very well for a B theorist. In fact, it seems quite sensible to me. It is a kind of nominalism about the phrase "the present." What Craig is saying here implies that there is no essence of "the present" but that we can use the phrase in various ways depending on what we want to talk about. Well and good, but it seems to me flatly impossible for a presentist to accept this view. To quote, again, from Craig's summary, presentism is
the doctrine that the only temporal entities that exist are present entities. According to presentism, past and future entities do not exist. Thus, there really are no past or future events, except in the sense that there have been certain events and there will be certain others; the only real events are present events.Craig's nominalist view about the duration of the present would imply that, if I choose to make "sessions of Congress" or "wars" my universe of discourse, the entirety of a session of Congress or of a war, with all the events that entails, over a period of years, can be in existence (for me?), can be the Real Now. Then again, someone else (e.g., a presentist insisting staunchly in philosophical conversation that entities of two years ago do not exist) may make his universe of discourse range only over individual seconds. For him, most of the events of the present session of Congress are excluded from the Now, and therefore the vast majority of those entities and events are non-existent.
This makes no sense whatsoever. This view could not be right if presentism were true. If one is a presentist, one cannot simply punt like this on the duration of the Real Now. Unless, perhaps, one wants to be a postmodernist, which I am quite sure Craig does not want to be!
The trouble for the presentist is that there is really no good solution to the question of the duration of the Real Now. It has been invested with enormous metaphysical importance but left undefined. Craig does a good and careful job surveying the options for defining it, and my conclusion is that his discussion shows the problem to be insoluble, though of course that is not the conclusion he draws.
I think that presentism is simply untenable as a position in the philosophy of time. To some degree, this should make people more friendly to the B theory, depending on what one thinks of the objections (which I don't have time to go into) to other A theories. Moreover, it should clear away certain obstacles to accepting God's timelessness. Craig himself places an enormous amount of weight in the case for putting God in time on the philosophy of time itself and, specifically, on the alleged superiority of presentism as a theory in the philosophy of time. In fact, he seems to imply that divine timelessness would be an attractive position if it were not for the fact that (he holds) the B theory is wrong and presentism is right. (Time and Eternity, pp. 111-112.) By that reckoning, if presentism is wrong, perhaps it isn't such a great idea to regard God as in time after all.
That, however, is a subject for another day.