Asymmetric temporal attitudes and time travel

Philosophers sometimes use thought experiments concerning the asymmetry of attitudes towards future and past events as arguments for a metaphysical asymmetry between past and future. For instance, the fact that I would prefer a much larger pain in my past to a smaller pain in the future is puzzling if the past and future are metaphysically on par.

Here’s a thesis I want to offer and briefly defend:

• It is not rationally consistent to give use thought experiments in this way and to accept the possibility of backwards time travel.

The reason is quite simple: if backwards time travel is possible, our asymmetric attitudes track personal time, not objective time. If I am going to travel 100 million years back in six minutes, I will prefer a smaller pain in five minutes to a much larger pain 100 million years ago, since both of these pains will be in my personal future and only a minute of personal time apart. But the metaphysical asymmetry between past and future tracks external time, not personal time.

"Now" and other indexicals (Language, Part IV)

In English, the pitch and rate at which one speaks typically do not affect the types of the tokens that one is using. Whether you say "home" quickly or slowly, with a low or a high pitch, your utterance is a token of one and the same type. But this need not be a universal truth. One can easily imagine a language where an utterance of "home" means one thing when spoken quickly and another when spoken slowly. In that case, there are two word types here, and which type one's token falls under will be partly determined by the sequence of phonemes and partly by the rate at which one speaks. (We might represent the two word types in writing as "home" and "h-o-m-e" if we wish.)

A language provides a mechanism for classifying linguistic tokens under linguistic types. There are very few restrictions on how the classification scheme can work, except contingent ones derived from our recognitional abilities. Imperceptible differences between tokens will not do the job.

It is quite possible, then, to have a language where the classification system is time-dependent. Thus, "home" at odd-numbered hours of the day means a tank, and at even-numbered hours it means an F-16. There are, thus, two word-types with the same phonemes, and to distinguish between them you have to check what time it is. Such a language might well be useful for confusing an evesdropping enemy.[note 1]

Imagine now a language L1 where the sound "chow" when uttered at a time t denotes the time equal to t+7minutes, when t is during an even-numbered hour, and denotes the time equal to t-7minutes, when t is during an odd-numbered hour, and where the type of the word is identified by both the sound "chow" and the time of utterance. This language can be understood as containing continuum many word-types, identified partly by the time at which the word-type is tokened and partly by the phonemes. This is a very odd language, but a possible one.

Observe that in L1 no utterance of "chow" is the utterance of an indexical. What an indexical refers to depends on both the token's type and on the context of utterance. But what "chow" refers to does not depend on the context of utterance, but only on the token's type. The token's type depends on the time of utterance, but that is a different matter.

Consider now a language L2 where the sound "fow" when uttered at a time t denotes the time t, and where the type of the word is identified by both the sound "fow" and the time of utterance. Just as no utterance of "chow" in L1 was an indexical, so no utterance of "fow" in L2 is an indexical. Rather, it is the utterance of a fine, upstanding, context-free referring term.

But now a question: How do we know that utterances of "now" in English are utterances of an indexical? Why not analyze utterances of "now" in English precisely the way utterances of "fow" are to be analyzed in L2? There are, I submit, no facts of linguistic practice (normative or not) that allow us to distinguish between English's "now" and L2's "fow". If linguistic facts supervene on facts of linguistic practice, there is no fact of the matter whether an utterance of "now" should be read as an indexical whose type is identified by the phonemes or as a non-indexical whose type is partly identified by the phonemes and partly by the time of utterance.

If we understand "now" along the lines of "fow", then any argument for the A-Theory of time based on our use of "now" is likely going to fail. For "fow" is perfectly at home in the eternalist world of the B-Theory. And what I said about "now" goes for tenses as well.

This strategy is closely parallel to the old failed B-theoretic attempt to translate "now" into the time of utterance. That attempt failed because when one translated "It is now 11:56 am", it translated into "It is 11:56 am at 11:55 am", and hence a sentence that one could reasonably be wrong about got translated into one that no one could be reasonably wrong about, which is absurd. On the present strategy, an utterance of "now" at 11:56 am does refer to the 11:56 am, indeed is rather like a proper name for it. In a sense "It is now 11:56 am" may be a tautology, but it is not a trivial tautology. Rather, it is like "Cicero is Tully" or "London is Londres."

If all this is right, then no deep facts about language hang on the distinction between indexicals and non-indexicals. There may be more than one way of classifying bits of utterances into types, and for any way of classifying that makes a bit of utterance into a token of an indexical, there is a way of classifying that makes that bit of utterance into a token of a non-indexical identified in some non-phonemic way. Each classification should give rise to the same proposition as expressed by the utterance as a whole.

A partial fix to Lewis's account of counterfactuals

A serious problem with Lewis's account of counterfactuals is that as Elga and Pruss have shown, Lewis's similarity account licenses errant counterfactuals of the form "Were B to occur at t₁, A would have occurred at t₀", where t₀ < t₁. A quick argument for this conclusion is as follows. We have good reason to think the universe's future is longer than the past. On the grounds of divine revelation this is clear: the future is forever but the world was created a finite amount of time ago. On the grounds of science this is also likely: the universe is expanding, and either it will extend forever, or it will eventually reverse and collapse, but even in the latter case we're not yet at the half-way point. Therefore, it seems, a world that exactly matches our world in all of the future but in very little of the past will always be more like our world than a world that matches our world in all of the past but in very little of the future. Hence, if we look at worlds close to ours in which the antecedent of a subjunctive holds, we will do better to look at worlds whose future matches the future of our world, and then retrodict to the past from the antecedent of the subjunctive.

But here is an interesting partial solution to this problem. Suppose we abandon Lewis's counterpart theory. Suppose, further, that we assume that all of the causal history of an event is essential to the event's identity. (It is plausible that some of the causal history is essential, but the possibility of drawing a line as to what is and what is not essential is implausible.) Now if exact match of spatiotemporal regions of worlds requires the numerical identity of the events in these regions, it is impossible for two worlds in which causation goes orthodoxly from past to future to match in the future but not in the past. The asymmetry in causation together with the essentiality of origins of events thus induces an asymmetry in counterfactuals, ruling out most backtracking counterfactuals. Of course Lewis wouldn't have liked this, since it means that causation is prior to counterfactuals.

Of course, other problems for Lewis remain.

Excluded Middle and an Open Future

Some people deny the Law of Excluded Middle (LEM--for all p, p or not-p) because they are convinced it leads to fatalism. But they really shouldn't deny LEM.

Suppose Helga is convinced that utilitarianism is true. You offer Helga a reductio argument against utilitarianism on the assumption that the hedonistic theory of happiness holds and another reductio argument against utilitarianism on the assumption that the hedonistic theory of happiness does not hold. Helga accepts both reductios and comes to deny hedonistic utilitarianism and non-hedonistic utilitarianism, but continues to accept utilitarianism. Pressed on how Helga's new position squares with logic, Helga asserts that based on her belief that utilitarianism holds, and her new beliefs that if hedonism holds, utilitarianism is not true, and if hedonism doesn't hold, utilitarianism is not true, she has concluded that LEM does not hold. There seems to be something irrational about this. Surely, she should either find fault with at least one of the reductios or abandon her belief in utilitarianism. It is hard to imagine premsies whose plausibility should trump LEM.

Arguments the depend on LEM are not, I think, uncommon in philosophy. If Molinism is true, evil and the existence of God are compatible (by Plantinga's free will defense). If Molinism is not true, evil and the existence of God are compatible (by Adams' free will defense). Hence, evil and the existence of God are compatible. It is pretty likely that Helga uses LEM-based arguments in other contexts, and it is pretty likely that the defender of the Open Future who denies LEM also uses LEM in other contexts.

Could they both say that LEM applies in some contexts (e.g., non-normative ones in Helga's case, or in ones that do not involve the future in the freedom case) but not others? Yes. But once we denied the plausible view that LEM follows from the meaning of the words "or" and "not", and denied the general intuition that between p and not-p tertium non datur, it seems that we have undercut the grounds we could have for thinking LEM holds even in those contexts in which it is supposed to hold in. Besides, the defender of the Open Future who denies LEM presumably does so on the basis of something like a temporalized modal logic according to which if p already holds, then not-p is no longer possible. But surely the principles of classical non-temporal non-modal logic are more plausible and more deeply embedded in our thinking than those of temporalized modal logic.

Anyway, it seems much better to hold on to LEM, and just deny the principle that if not(will(p)), then will(not-p), where "will(p)" means p will hold. The principle that if not(will(p)), then will(not-p) is a dubious one if we see "will" as a modal-type operator, maybe akin to "would" except for being a one-place operator, and that is precisely how we will see "will" if we have presentist or growing-block intuitions. Moreover, it is a principle that is less central to our thinking than LEM, particularly because it applies only to our thinking about the future, while LEM applies to all our thinking. It seems clear to me that this is what the person impressed by the argument for logical fatalism should say, boldly holding that there is a fact of the matter whether Jones will mow the lawn tomorrow: it is false that Jones will mow the lawn tomorrow, just as it is false that he will fail to mow the lawn tomorrow. And God's omniscience will be unrestricted: he knows that it is false that Jones will mow the lawn and that it is false that he will not mow the lawn.

Of course, it's best to hold on to both LEM and if not(will(p)), then will(not-p).