Truth, logic and explanation

Consider the following two very plausible explanatory intuitions:

1. Roses are flowers or violets are yellow because roses are flowers.
2. "Roses are flowers or violets are yellow" is true because "Roses are flowers" is true or "Violets are yellow" is true.

Now, the intuition in (1), when generalized to the general principle that if p and not q, then p or q because p, yields:

3. "Roses are flowers" is true or "Violets are yellow" is true because "Roses are flowers" is true.

Explanation may or may not be transitive in general, but it seems correct in the case at hand to move from (2) and (3) to:

4. "Roses are flowers or violets are yellow" is true because "Roses are flowers" is true.

Observe that (1) and (4) are parallel. Now suppose we agree with the deflationist about truth that:

5. "Roses are flowers or violets are yellow" is true because roses are flowers or violets are yellow.

We now have two paths to explaining why "Roses are flowers or violets are yellow" is true. One explanation is (4) and the other is (5). Unless one of these two explanatory paths subsumes the other, it seems that we have a case of explanatory overdetermination. But neither path subsumes the other. First, the explanans in (4) does not explain the explanans in (5), since that "Roses are flowers" is true does not explain why it is that roses are flowers or violets are yellow, as the former is a fact about a sentence (we can also make the argument go with utterances, statements or propositions) while the latter is a fact about flowers. Second, the explanans in (5) does not explain the explanans in (4)—for that "Roses are flowers" is true may be explained by roses being flowers, but is surely not explained by roses being flowers or violets being yellow.

Thus, the deflationist who accepts (1) and (2) is pressed to accept that (4) and (5) are an overdetermining pair of explanations. But that is unappealing. Probably the deflationist will have to deny the Tarskian intuition in (2). I don't know how great the cost of that is.

So what should we say if we accept (1)-(4), and we are inflationists? We still have a bit of a puzzle, even if we deny (5). The problem is that the explanations in (1) and (4) are exactly parallel. But, we ask, what explains this parallelism? It seems too much to separately explain the truth of the disjunction by the the truth of the true disjunct, and to explain the disjunction by the true disjunct. There should be a way of unifying this. One way would be:

6. (a) Roses are flowers or violets are yellow because "Roses are flowers or violets are yellow" is true; (b) "Roses are flowers or violets are yellow" is true because "Roses are flowers" is true; and, finally, (c) "Roses are flowers" is true because roses are flowers.

(Or we can give a propositional variant. That would probably be better, but I'll stick to the linguistic here so I don't have to keep on saying "the proposition that...". And maybe to explain "Roses are flowers" being true we need a few more steps on the linguistic side—but maybe not, since it may be a logically simple claim about the natural kinds rose and flower rather than a quantified claim.) On this perhaps weird approach, the explanation in Tarski's Schema (T) sometimes goes in one direction and sometimes in the other. I don't fully like this weird approach, though, because step (b) is troubling. The obvious way to justify the explanation in step (b) seems to be: (bi) "Roses are flowers or violets are yellow" is true because "Roses are flowers" is true or "Violets are yellow" is true; and (bii) "Roses are flowers" is true or "Violets are yellow" is true because "Roses are flowers" is true. However, if (bii) has no further intermediate steps, then, by the same token, (1) shouldn't have any further intermediate steps, and (6) is wrongheaded. And if (bii) has further intermediate steps, then these steps will need to be expanded in the fashion of (6), which will result in circularity.

Maybe, though, we can get away with just making (6b) be immediate in the case where "Roses are flowers" is true. In that case, what makes certain complex apparently worldly facts true is stuff on the linguistic side, finally combined with something more basic on the worldly side. I suppose this is basically what Tarski was up to. A lesson of this approach would be that logically complex facts, like the fact that roses are flowers or violets are yellow, are very different from simpler ones.

Of course, if it can be shown that "explains" is used equivocally in (1)-(4), or that the instances of transitivity that I employed are unjustified, all of this goes out the window. But I do think that this may give some reason to be an inflationist about truth.

Telekinesis and the unreality of artefacts

Telekinesis is not within our power. How can we formulate this fact? Well, it's a bit tricky. The natural way of formulating is to say that no human thought has a physical effect outside the body except through an extra-mental bodily movement (this formulation leaves open the possibility that the mind is a part of the body). However, we can, just by thinking about it, change the positions of needles on gauges on a neural scanner. And if Christians are right, it is possible to pray mentally for a physical effect, and have the physical effect occur by a divine intervention. Moreover, we want to insist that just as one person can't do telekinesis by herself, so too a dozen can't do it together.

One way to handle the neural scanner concern and to extend to the case of multiple agents is to say that whenever human thoughts have a physical effect in virtue of their content, they do so through causing at least one an extra-mental bodily movement. The case of miracles can be handled, perhaps, by adding a qualifier "except for miracles".

Now, suppose that tables, chairs and other artefacts exist. Then, I think, the existence of an artefact depends crucially on what people think: it depends on the intentions of the artificer and what other people plan to use it for. We could imagine a physical object just like a chair but which can survive the loss of all of its legs, because its purpose is quite different from the purposes of a chair. Whether that object exists or whether a chair exists in its place depends on what people made the object for, and/or what they plan to use it for. Likewise, whether one is making a palisade—a single object—or a series of upright pointed sticks tied together depends on one's intentions for the project. If, for instance, one is planning to untie all the sticks and use them as spears as soon as the enemy approaches, then what one has made is a bunch of spears tied together for ease of storage, and one has not made a palisade. Thus, the number of artefacts depends on the contents of our thoughts.

Facts about what artefacts exist depend crucially on the content of what people think. Since many artefacts, including the ones in the above examples, are physical objects outside of human bodies, it follows from the above, that if there really are artefacts, then the contents of thoughts can affect what kinds of and how many physical objects exist outside of human bodies. Moreover, this happens without any miracles, in the ordinary course of things. Hence, if there really are artefacts, there is something very much like telekinesis.

Of course, nobody really thinks there is some miraculous multiplication or aggregation, respectively, of objects when a bunch of spears tied together or a palisade, respective, is made. The reason for that is that we realize, perhaps inconsistently, that artefacts are not real things.

There is a way out of this argument, and this is to assume compositional universalism. But that faces at least one serious problem, as an earlier post has shown.

Presentism

On one of the best presentist accounts we have, namely that of Trenton Merricks, statements that some proposition p was or will be true are to be understood as embeddings of p in the context of a was or will modal operator, which modal operators are analogous to modal operators like M (possibly) or L (necessarily) or in a work of fiction or ought to be the case. Moreover, even if p is the sort of proposition to normally have a truthmaker, was(p) and will(p) do not have a truthmaker. Call this "modalist presentism."

Here is a problem for modalist presentism. There are a number of contexts in which we stand in the same kind of relation to a proposition about the past or the future as to an analogous proposition about the present. One kind of case I've already discussed in another post, the case of induction: we treat claims about past, present and future on par with respect to induction. A different set of cases are provided by certain non-first-person attitudes (this idea comes from Parfit). If my child is to undergo a painful medical procedure this afternoon, I will be pained at his undergoing the painful experience. Suppose that I am today out of causal contact with my child. I do not think it should matter much to my attitude right now towards the child's experience whether the experience has just occurred, or is now occurring, or is about to occur. And even if there is a difference, there is a common core of compassion in all three cases. Similarly, if I have heard that a friend will today receive a teaching award, I will be glad for his sake. Supposing I am unable to attend the ceremony, it will not matter vis-à-vis my gladness whether he has received the award five minutes ago, or is receiving it now, or will received it in five minutes.

The non-presentist has a way of explaining and justifying the common core of the inductive and emotional attitudes: in all cases, the attitude is a response to the reality of some situation. The feeling I have towards my child's actual pain, whether past, present or future, is different in kind from the feeling that I have towards facts of the form Q(my child is in pain) where Q is some modal operator like M or in a work of fiction. (The case of L is different, but that is because Lp entails p.) Likewise, I treat past, present and future occurrences on par for inductive purposes, and recognize the difference between these and possible or fictional occurrences. In fact, we might even say that a good test for whether I take a situation to be real is whether the situation enters into my inductive and emotional attitudes in these kinds of ways.

But for the modalist presentist, my child's having suffered pain is related to my child's presently suffering pain in somewhat way that my child's possibly suffering pain is related to my child's actually suffering pain. So now we have a problem for the presentist: to explain why it is that there is a pattern of attitudes that are equally appropriate towards situations within the scope of was and will operators as towards present situations, without adverting to the reality of these situations.

Here's a different way of formulating the worry, one that will affect even non-modalist presentists. It seems that what makes it appropriate to have the same attitude of grief or joy at various true propositions, and to engage in inductive reasoning about such propositions, is that these propositions have a truthmaker homogeneity: they are all made true by similar kinds of things. But the presentist denies truthmaker homogeneity between reports of past, present and future pains, as well as between reports of past, present and future raven blackness. The present-tense reports have ordinary sorts of truthmakers, like black ravens or people suffering. The past and future tense ones either have no truthmakers (Merricks) or have truthmakers of a significantly different sort (Bigelow, Crisp) from the present tense ones.

It might be thought that while the presentist has trouble explaining and justifying the lack of difference in these kinds of attitudes, the eternalist has trouble explaining and justifying the difference in first-person attitudes. I care a lot about whether a painful experience is past, present or future. But this is not a problem for the eternalist. For the justification of an attitude often lies not just in the objective features of the situation towards which one has the attitude, but also in a relation to the situation. That a situation is earlier than, simultaneous with or later than an attitude can affect whether the attitude is appropriate or not. And this indexical difference seems to matter a lot more in the case of situations that involve one oneself.