The Review of Metaphysics

An extreme version of the view that the past is necessary while the future is not is held by Arthur Prior (1914–1969), whose claim is that in the case of the future there may be no present fact of the matter about whether a proposition is going to be true or false. In particular, future contingents—statements still open to human choice or mere chance— are neither true nor false. The view that future contingents do not have exactly one of two truth values played an important part in the development of Prior’s tense logic. We find it in Formal Logic, Time and Modality, Past, Present and Future, and in many of the articles collected in Papers on Time and Tense and Papers in Logic and Ethics.¹ While Prior’s views on many things certainly changed over the years, his work on determinism can easily be seen as presenting a unified doctrine. Prior takes it as obvious that future contingents lack a truth value, and that it is the job of tense logic to provide an articulation of this position. It is convenient to address his reasons by looking at two claims, both of which he endorses. The first is that the future truth or falsity of such statements is incompatible with a world in which humans are capable of free action; and the second is that it compromises God’s omniscience.

Prior is not alone in his assumption that free will is incompatible with future truth or falsity. Many scholars have taken chapter 9 of Aristotle’s On Interpretation in this way.² This chapter is known to philosophers because of Aristotle’s example of tomorrow’s sea battle: [End Page 309]

Moreover, if it is true to say that something is white and large, both have to hold of it, and if true that they will hold tomorrow, they will have to hold tomorrow; and if it neither will be nor will not be the case tomorrow, then there is no ‘as chance has it’. Take a sea-battle: it would have neither to happen nor not to happen. ³

Not everyone took Prior’s view of Aristotle, and this is where Boethius becomes significant. In his second commentary on On Interpretation Boethius considers Aristotle’s argument: “For Aristotle does not say that both are neither true nor false, but, of course, that each of them is either true or false—not, however, definitely, as with those having to do with past matters or those having to do with present matters.”⁴ The passage undoubtedly causes problems of interpretation. Boethius probably means that Aristotle is saying that from the necessity of the fact that any statement must be either true or false it does not follow that it must be true, or that it must be false. This of course does not yet provide an argument against the claim that truth values for future contingents lead to determinism. For that we need to move to The Consolation of Philosophy:

For we see many things with our eyes while they are in doing, as those things which the coachmen do while they drive and turn their coaches and in like manner other things. Now doth necessity compel any of these things to be done in this sort? No. For in vain should art labour if all things were moved by compulsion. Wherefore, as these things are without necessity when they are in doing, so likewise they are to come without necessity before they be done. And consequently there are some things to come whose event is free from all necessity. For I suppose no man will say that those things which are done now were not to come before they were done. Wherefore these things even being foreseen come freely to effect. For as the [End Page 310] knowledge of things present causeth no necessity in things which are in doing, so neither the foreknowledge in things to come. ⁵

What Boethius is telling us is that whether or not an action is free does not depend...