How to Predict Future Contingencies İlhan İnan

Transcription

1 Abstract How to Predict Future Contingencies İlhan İnan Is it possible to make true predictions about future contingencies in an indeterministic world? This time-honored metaphysical question that goes back to at least Aristotle still perplexes philosophers. In this paper, rather than proposing a solution to the problem, I cast doubt on a recent attempt towards a solution, advocated by J. MacFarlane, that relativizes truth to a context of assessment, as well as a context of utterance. I show that the argument MacFarlane gives to this end equivocates between two senses of what he calls the determinacy intuition ; I argue that when the term is taken in one sense, then MacFarlane s position becomes futile; and when taken in the other sense it refers to an intuition that the indeterminist would normally deny. Furthermore, once we grant the indeterminist the truth of such an intuition, I show that MacFarlane s theory not only relativizes truth, but our notion of contingency as well. I then show that even a further attempt to save the position by adding a future time-index to such predictions ends up in failure. Keywords: future, contingency, truth, Aristotle, indeterminism, relativism If the facts today, together with the laws of nature, do not guarantee that there will be a sea battle tomorrow, then it would seem to follow that saying that there will be a sea battle tomorrow is neither true nor false today. 1 However, if the sea battle does in fact take place tomorrow, then it would appear to be correct to say tomorrow that what we had said turned out to be true. Prima facie this looks problematic. In a recent paper 2, J. MacFarlane argues that by relativizing the truth of a sentence to a context of assessment as well as a context of utterance we can find a reconciliation. Though I am inclined to agree with MacFarlane that a reconciliation can be achieved, his argument to establish this, I believe, is quite unacceptable. Here is how J. MacFarlane poses the problem:

2 Suppose that the world is objectively indeterministic. In some possible futures, there is a sea battle tomorrow. In others, there is not. How should we evaluate an assertion (made now) of the sentence There will be a sea battle tomorrow? The question is difficult to answer because we are torn between two intuitions. On the one hand, there is a strong temptation to say that the assertion is neither true nor false...i shall call this the indeterminacy intuition. On the other hand, there is a strong temptation to say that the assertion does have a definite truth-value, albeit one that must remain unknown until the future unfolds. After all, once the sea battle has happened (or not), it seems quite strange to deny that the assertion was true (or false). I shall call the thought that the assertion does have a definite truth-value the determinacy intuition. (MacFarlane, p.321) Note that the two intuitions that MacFarlane talks about are supposed to be intuitions that an indeterminist has; if the determinacy intuition is what a determinist has, and the indeterminacy intuition is what an indeterminist has, then arguing that there is way to reconcile these intuitions would in effect be to argue that there is way to reconcile determinism with indeterminism. I take it that this is not what MacFarlane attempts to accomplish. So then we should ask: do indeterminists really have the determinacy intuition as MacFarlane seems to take for granted? After all once the sea battle takes place, an indeterminist may not think that it is quite strange to deny that the assertion was true, and simply claim that the asserted proposition was neither true nor false yesterday and true today. If the determinacy intuition is the intuition that a sentence that expresses a future contingency has a definite truth value at the time of utterance, I strongly doubt that we could find a single figure in the history of philosophy who was an indeterminist and had such an intuition, while holding on to the indeterminacy intuition. To be more charitable let us acknowledge that MacFarlane is concerned not with the truth of the sentence that expresses a future contingency, but rather with it s utterance with assertive intent, i.e. an assertion. Let us then distinguish between an assertion (i.e. the

3 speech act of uttering a sentence in a context with assertive intent), the uttered sentence, and the proposition expressed by that sentence. We may then say that our truth predicate applies to assertions in the following way: an assertion is true in a context when the proposition expressed by the asserted sentence is true in that context. So then the determinacy intuition may be taken to be view that the assertion of a future contingency has a definite truth value at the time of utterance. There is, however, another way to interpret the determinacy intuition that would seem to make more sense, which in fact is suggested by another passage in MacFarlane s article, but before we get into that let us see how MacFarlane diagnoses the source of the problem: Are they [the two intuitions] not incompatible? Only in the presence of the orthodox assumption that the truth for utterances is non-relative. I shall call this assumption the absoluteness of utterance-truth...on the orthodox view if we say that an assertion of There will be a sea battle tomorrow is neither true nor false when it is made, then we cannot allow that it might acquire a truth-value later...(p.322) It may appear that by the absoluteness of utterance-truth, MacFarlane refers to the thesis that the proposition expressed by an uttered sentence has an eternal truth value or an eternal truth value gap; a proposition that is true (or false) is eternally true (or false), and one which is neither true nor false is eternally neither true nor false. Taken as such this really is not an orthodox assumption, for there are many indeterminists, starting perhaps from Aristotle himself (at least under the standard interpretation) who hold that a proposition about a future contingency lacks a truth value until a certain moment in time and acquires a truth value thereafter. For instance regarding the sea battle, indeterminists who have the indeterminacy intuition claim that the proposition expressed by

4 (1) There will be sea battle tomorrow is neither true nor false today, but will be either true or false tomorrow, which simply implies the negation of the absoluteness of utterance-truth taken in this way. So this cannot be what MacFarlane has in mind. Given that MacFarlane refrains from talking about the truth value of the proposition, this is not how we should interpret the thesis. Rather, as I understand him, by the absoluteness of utterance-truth he refers to the following general principle: If an utterance is made at time t in context c, then whether that utterance is true, false, or neither true nor false in c will remain the same for any time after t. Interpreted in this way this principle implies that if an utterance of (1) is neither true nor false on the day in which it is uttered, then it will always be the case that it is neither true nor false on the day in which it is uttered. To express this in non-indexical terms, let d 0 be the name of the day in which (1) is uttered, and let d 1 be the name of the next day. Now (1) as uttered on d 0 has the same truth conditions as (2) There is a sea battle on d 1 as uttered on d 0. It seems clear to me that indeterminists who have the indeterminacy intuition deny that an utterance of (2) has an absolute truth value, and therefore this, I take it, is not the orthodox view MacFarlane wishes to deny. However saying that

5 (3) The utterance of there is a sea battle on d 1 is neither true nor false on d 0 expresses an absolute truth, is what perhaps all indeterminists who have the indeterminacy intuition hold. This is what I believe MacFarlane wishes to challenge: we must reject the absoluteness assumption. We must relativize the truth of utterances to a context of assessment, and we must relativize the truth of sentences to both a context of utterance and a context of assessment. (p.322) Given this form of relativizing truth, MacFarlane goes on to argue that if yesterday Jake uttered (1), then what he said was neither true nor false when assessed yesterday, but was true when assessed today (given that the sea battle takes place.) Again we are not supposed to interpret this to mean that the proposition expressed by (1) was neither true nor false yesterday but true today; rather his claim is that the utterance of (1) was neither true nor false yesterday as assessed yesterday, but was true yesterday as assessed today. Such a view implies that (3) is true when assessed on d 0 but false when assessed on d 1. This, no doubt, is a very radical claim. Now, as I pointed out in the beginning, the determinacy intuition may be taken in another way. After uttering (1) yesterday, if Jake observes today that there in fact is a sea battle taking place, he may wish to say, (4) What I said yesterday was true, but he may also wish to say,

6 (5) What I said yesterday turned out to be true. It seems to me that there is an important difference between (4) and (5), for an indeterminist who holds that (1) expressed a future contingency that had no truth value at the time of utterance (yesterday) would not normally hold that (4) expresses a truth today, whereas he could hold that (5) does. 3 However MacFarlane seems to think (4) and (5) amount to the same thing: But now what about someone who is assessing Jake s utterance from some point in the future? Sally is hanging onto the mast, deafened by the roar of the cannon. She turns to Jake and says Your assertion yesterday turned out to be true. Sally s reasoning seems unimpeachable: Jake asserted yesterday that there will be a sea battle today. There is a sea battle today So Jake s assertion was true. (p.325) This certainly does look like an impeachable piece of reasoning by Sally. There may be a sense in which Jake s assertion turned out to be true, though that hardly shows that it was true yesterday. If Sally is an indeterminist who holds that the facts of yesterday did not ensure that a sea battle would take place today, and has the indeterminacy intuition, then I do not see on what grounds she would wish to tell Jake that what he said was true. It is this equivocation that makes what MacFarlane calls the determinacy intuition ambiguous: there is the intuition that (4) is true, and there is the intuition that (5) is true, which are two separate intuitions. I would assume that indeterminists would not normally have the former intuition, whereas they might have the latter one. So if we understand the determinacy intuition in the latter sense, we would hold that what Jake said yesterday is

7 true today not that it was true yesterday: today s sea battle cannot change the fact that what Jake said yesterday was neither true nor false yesterday. Now going back to MacFarlane s basic claim: what does it mean to say that yesterday s utterance was neither true nor false when assessed yesterday but true when assessed today? One possible interpretation would be that the proposition expressed by the uttered sentence of yesterday was neither true nor false at the time of utterance, namely yesterday, but is true today. This, however, is no radical view, and does not in any way imply that the utterance was true at the time when it was uttered. But if we wish to hold on to the determinacy intuition taken in the former sense (which makes (4) true), then we should read the statement as saying that yesterday s utterance was neither true nor false as assessed yesterday, but was true assessed today. Now, to claim that yesterday s utterance was true yesterday, should mean that the proposition expressed by the uttered sentence was true yesterday (as we assess it today). If so, then assuming that Jake subscribes to MacFarlane s thesis, he could have had the following conversation with Sally: Sally: You said yesterday that there would be a sea battle today, and what you said turned out to be true. Jake: Yes, indeed! In fact what I said yesterday not only turned out to be true, but it was true yesterday. Sally: So then, it was already true yesterday that there would be a sea battle today. Jake: Surely!

8 If Jake subscribes to the indeterminacy intuition, I do not see how this dialogue could be considered to be reasonable. What is worse is that Jake could now take a further step and argue that the sea battle was not a contingency. That is because, given MacFarlane s position, it would appear that the contingency of an event would also have to be relativized to a context of assessment. I would think that ones who have the indeterminacy intuition subscribe to the following general principle: IP. If an utterance made at t 0 expresses a proposition about some future event to take place at t 1, and the utterance is true at t 0, then that event is not a future contingency. We can now show that the sea battle taking place is a contingent event when assessed yesterday, but a non-contingent one when assessed today. Being an indeterminist, Jake, yesterday could have said: the sea battle taking place tomorrow is a future contingency. However once he observes the sea battle today, he could correctly say, on MacFarlane s view, that it was already true yesterday that there would be a sea battle today. Therefore, as Jake assesses the event today, by using IP, he could claim that today s sea battle was not a contingency, and then he could conclude that it was already determined yesterday that there would be sea battle today. Now perhaps MacFarlane would want to relativize IP as well to a context of assessment, and claim that when we assess IP at t 0 it would be true, but when we assess it at t 1 it would be false. Or he may wish to modify IP, by inserting the context of assessment into it, so that it suits his thesis. Such attempts, however, will simply be technical ad hoc maneuvers, distorting the intuitive idea that an assertion about a future contingency lacks a truth value antecedently.

9 Now one may suggest that there is a way to overcome this difficulty by slightly modifying our utterances about future contingencies. Suppose that Jake, holding on to the indeterminacy intuition, rather than uttering (1), more cautiously utters: (6) That there will be a sea battle tomorrow will be true tomorrow. It may appear as if the contingency of the sea battle now would not be jeopardized. There are further difficulties however. When the sea battle does in fact take place the next day (on d 1 ), then it would follow that Jake s utterance of (6) was true on the previous day (on d 0 ). Following MacFarlane, this would have the implication that an utterance of (6) is true on d 0 as assessed on d 1. In other words on d 1 we could say that Jake s utterance of (6) was already true on d 0. So then on d 1 we could truthfully utter that it is true today that there is a sea battle was already true yesterday. Intuitively this simply strikes me as being a false claim given that the sea battle was a future contingency. It should be correct say that if an utterance expresses a contingency, then that that utterance is true also expresses a contingency. If so, this time the contingency of it being true that the sea battle takes place would have to be relativized to a context of assessment. As I proposed in the beginning there is a way to reconcile the determinacy and the indeterminacy intuitions. When we make an assertion about a future contingency, the indeterminacy intuition suggests that what we say has no truth value. When the event in question later does in fact take place, then it would be correct to say that what we had said turned out to be true. This simply could be taken to mean that what we had asserted was neither true nor false at the time of utterance, but the very same assertion is now true.

10 If assertions are the right kind of things that our truth predicate applies to, as MacFarlane presupposes, then I see no problem in holding that the truth predicate could correctly apply to an assertion about a future contingency, not at the time of utterance, but at a later moment in time. If so, then it should be correct to say that we can make true-to-be predictions about future contingencies in this qualified sense; our predictions would not be true at the time they are made, but they could become true when the time comes. I do not see why such a reconciliation should not satisfy us. And if it does satisfy us, we shouldn t be forced into saying that a past utterance expressing a future contingency was true, as long as we have the indeterminacy intuition. 1 The debate on future contingencies goes back to Aristotle's De Interpretatione, Chapter IX in which he gives the famous "sea battle" example, which still serves as a paradigmatic case in contemporary literature on the matter. 2 MacFarlane, J. (2003) Future Contingents and Relative Truth, The Philosophical Quarterly, Vol.53, No.212 (pp ). 3 Here is a case that clearly marks the difference: If we were to point to a picture of a young boy and exclaim he turned out to be a criminal!, that certainly does not imply that the he was a criminal as a boy. I would like to thank Stephen Voss for this analogy and other valuable comments he gave on an earlier draft. Selected Bibliography on Future Contingencies Albritton, R., Present Truth and Future Contingency, The Philosophical Review, Vol. 66, No. 1. (Jan., 1957), pp Anscombe, G.E.M., "Aristotle and the Sea Battle", Mind, Vol. 65, No. 257 (Jan., 1956), pp Belnap, N. et.al., Facing the Future, New York: Oxford University Press,

11 Belnap, N., "Branching Space-time", Synthese, 92 (1992), pp Broome, J., Discounting the Future, Philosophy and Public Affairs, Vol. 23, No. 2. (Spring, 1994), pp Cahn, S.C., Statements of Future Contingencies (in Discussions), Mind, New Series, Vol. 83, No.332. (Oct., 1974), p Dewey, J., Events and the Future, The Journal of Philosophy, Vol. 23, No. 10. (May 13, 1926), pp Ducasse, C.J., Truth, Verifiability, and Propositions about the Future, Philosophy of Science, Vol. 8, No. 3. (Jul., 1941), pp Edwards, P., Necessary Propositions and the Future, The Journal of Philosophy, Vol. 46, No. 6. (Mar. 17, 1949), pp Feinberg, G., Lavine S., Albert D., Knowledge of the Past and Future The Journal of Philosophy, Vol. 89, No. 12. (Dec., 1992), pp Fisher, J., Fallibility and Knowledge of the Future, Philosophy and Phenomenological Research, Vol. 36, No. 1. (Sep., 1975), pp Forbes, G., Logic, Logical Form, and the Open Future, Noûs, Vol. 30, Supplement: Philosophical Perspectives, 10, Metaphysics, (1996), pp Gustafson, D.F., Assertions about the Future (in Discussion), Philosophy and Phenomenological Research, Vol. 26, No. 3. (Mar., 1966), pp Hintikka, J., The Once and Future Sea Fight: Aristotle s Discussion of Future Contingents in De Interpretatione IX, The Philosophical Review, Vol. 73, No. 4. (Oct., 1964), pp Ihrig, A.H., Remarks on Logical Necessity and Future Contingencies, Mind, New Series, Vol. 74, No (Apr., 1965), pp Kavka, G. S., The Paradox of Future Individuals, Philosophy and Public Affairs, Vol. 11, No. 2. (Spring, 1982), pp Margolis, J., Statements about the Past and Future (in Discussion), The Philosophical Review, Vol. 72, No. 1. (Jan., 1963), pp Maxwell, N., On Relativity Theory and Openness of the Future (in Discussion), Philosophy of Science, Vol. 60, No. 2. (Jun., 1993), pp Mayo, B., The Open Future, Mind, New Series, Vol. 71, No (Jan., 1962), pp McArthur, R.P., Factuality and Modality in the Future Tense, Noûs, Vol. 8, No. 3. (Sep., 1974), pp Montague, R., Mr. Bradley on the Future (in Discussions), Mind, New Series, Vol. 69, No (Oct., 1960), pp

12 Murray, M.J., Leibniz on Divine Foreknowledge of Future Contingents and Human Freedom, Philosophy and Phenomenological Research, Vol. 55, No. 1. (Mar., 1995), pp Oppy, G., On An Argument About Reference to Future Individuals (in Discussions), Philosophical Quarterly, Vol. 45, No (Jan., 1995), pp Philosophy and Phenomenological Research, Vol. 54, No. 4. (Dec., 1994), pp Prior, A.N., Three-Valued Logic and Future Contingents, Philosophical Quarterly, Vol. 3, No. 13. (Oct., 1953), pp Radden, J., Second Thoughts: Revoking Decisions Over One s Own Future Ranken, N.L., A Note on Past and Future Futures (in Discussion), Philosophy and Phenomenological Research, Vol. 27, No. 4. (Jun., 1967), pp Rankin, K. W., Past and Future, Philosophical Quarterly, Vol. 17, No. 69. (Oct., 1967), pp Scheer, R.K., Knowledge of the Future, Mind, New Series, Vol. 80, No (Apr., 1971), pp Schindler, P., Tense Logic for Discrete Future Time, Journal of Symbolic Logic, Vol. 35, No. 1. (Mar., 1970), pp Sklar, L., Up and Down, Left and Right, Past and Future, Noûs, Vol. 15, No. 2. (May, 1981), pp Stenner, A.J., On Predicting our Future, The Journal of Philosophy, Vol. 61, No. 14. (Jul. 16, 1964), pp Stocker, M., Mayo on the Open Future (in Discussions), Mind, New Series, Vol. 74, No (Apr., 1965), p Taylor, R., The Problem of Future Contingencies, The Philosophical Review, Vol. 66, No. 1. (Jan., 1957), pp Teichmann, R., Future Individuals, Philosophical Quarterly, Vol. 41, No (Apr., 1991), pp Thomason, R.H., "Indeterminist Time and Truth-Value Gaps", Theoria, 36 (1970), pp Will, F.L., Skepticism and the Future, Philosophy of Science, Vol. 17, No. 4. (Oct., 1950), pp Williams, D., Induction and the Future (in Discussions), Mind, New Series, Vol. 57, No (Apr., 1948), pp Williams, G., Freedom of Choice in the Pre-Determined Future (in Discussions), Philosophy and Phenomenological Research, Vol. 12, No. 1. (Sep., 1951), pp