- Traditionally there have been three competing philosophical views about the ontological status of the future. Each theory gives a different answer to such questions as
Now suppose that we regard Einsteinian Relativity as making plausible claims about the actual structure of physical space-time, and not as a set of fictions or a mere computational device for cranking out predictions. Then we are forced at least to replace the traditional philosophical views with more subtle formulations which take into account the relativity of simultaneity and of "the future."
- whether or not the future is as "real," "actual," or "determinate" as the present and the past;
- whether or not every statement about the future is true unless false; and
- whether or not we can succeed in referring to future particulars.
- But it is not clear that each of the traditional views can be restated in a way that allows it to retain whatever plausibility its defenders thought it had. Some suspect that only one of the traditional views is compatible in spirit with Special and General Relativity and thus survives the restatement. But to be sure of this we should explore in detail the different ways of reformulating the other theories. After describing the traditional philosophical theories in the traditional terms, I would like to see how they can be reformulated to accommodate Relativity, so that their defenders can see for themselves whether or not they still seem acceptable in their new, relativistic clothing.
- The first of the traditional views, the "Empty-future theory," holds that the future is "unreal" or not yet "actual." Unlike the present and the past, it is literally nothing. So logically contingent statements positing specific future events, things, or states of affairs ("particulars" for short) are as yet neither true nor false. Those statements, or their present-tense counterparts, will become true or false when the future events predicted actually occur or fail to occur as predicted. We cannot succeed in referring to future particulars, such as my first great-grandchild, for they do not exist (tenseless), and it is not yet true or false that they will exist. The Empty-future theory is defended by C. D. Broad in chapter II of his Scientific Thought.
- The second traditional view, the "Full-future theory," holds that the future, like the present and the past, is fully real, actual, and determinate. The principle of bivalence is held to apply to all meaningful statements about the future; each such statement is either true or false, unless deprived of truth value because of some independent flaw, such as excessive vagueness, which can mar statements about present and past as well. Future particulars, like present and past ones, can be designated by referring expressions. The theory as such does not state that all future particulars are causally determined by present or past ones, though its opponents sometimes charge — mistakenly, I believe — that it entails universal causal determinism. The Full-future theory is sometimes called the "block-universe theory," though that tag sometimes covers other views, such as the view that time or change are not fully objective but in some sense anthropocentric or subjective. Donald Williams, in "The Sea Fight Tomorrow," gives a classic defense of the Full-future theory. This view has the best prima facie chance of surviving restatement along relativistic lines, since Relativity tends to blur the old hard and fast distinctions between past and future, and this view denies that they are distinguished in ontological status.
- The third traditional position I will call the "Halfway theory," since it is a compromise position between the Full- and Empty-future theories. The Halfway theory holds that the future is real or ontologically determinate only to the extent that it is causally determined by present or past particulars. The categorical version states that in fact the future is not completely determined causally by present and past. The hypothetical version says simply that if it is not so determined, then to that extent it is unreal, but the question of complete determinism is left open. Both versions hold that statements about the future are true now if the future is causally determined to turn out as they predict; false, if it is causally determined that the future will not be what they say; and neither true nor false if the future is not causally determined either way. Halfway theorists generally do not make clear what conditions must hold if referring expressions that purport to designate future particulars are to succeed in referring to them. The Halfway theory has often been attributed to Aristotle on the strength of the famous sea-fight passage in "Aristotle - De Interpretatione, Chapter 9", but alas, the attribution has almost as often been questioned.
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