- There is a strong intuition, shared by many, that, whatever other meanings 'probability' has, there is at least one sense of that word in which it expresses an objective property of "the world"; that is, a property of things or of states of affairs which is present and determinate irrespective of human descriptions of the nature of things and of human knowledge of the actual state of affairs. Attempting to state just exactly what this property is, however, is a task of notorious difficulty. Numerous extended attempts have time and time again fallen to rather devastating criticisms from proponents of other views on probability.
- There is one "objectivist" view, expressed in one version by Peirce, and perhaps by Fisher, at least implicitly, which has recently been re-expressed. This is that probability is a dispositional property of "the world," a property that can be fully analyzed by reference to objective properties of things or of states of affairs, but only if the analysis makes use of the subjunctive mood. There are, at least, two quite different theories of probability that come under this general heading. In one, the suggestion is made, at least implicitly, that the subjunctive analysis needed is straightforward, probability being analyzed in terms of what would be the limits of relative frequencies of outcomes in possible sequences of experiments. This is, I believe, Popper's view. The other position, that of Hacking, superadds to the "dispositional" approach a theme derived from Braithwaite: that the meaning of a probability assertion is to be found, at least in part, in the rules adopted for the acceptance or rejection of attributions of particular degrees of probability to particular outcomes.
- I propose to examine the metaphysics of the dispositional view in some detail. I shall, however, devote my attention to only the former of the two positions I have just outlined. I believe that the results obtained are relevant to a critique of theories of the second kind, but I shall not attempt to establish this.
- Popper has claimed that the dispositional approach is a significant advance on earlier objectivist theories. He has claimed for it two distinct advantages: first, that it eliminates residual subjectivistic elements from the objectivist account; second, that it provides us with a theory of objective probability which clarifies the peculiar status of probability attributions in quantum theory1.
- I shall argue that the dispositional theory, far from being an improvement upon the older objectivist theories, is, on the contrary, worse off from the point of view of containing "latent" subjectivistic elements. I also believe that the theory does very little to clear up the mysteries of the interpretation of quantum mechanics2, but I shall not argue for this. I shall argue, however, that quantum theory3 does provide a context in which it is at least arguable that some of the difficulties with the objectivist, dispositional approach which I bring forward appear less intimidating. That is, although the dispositional theory may not help us much at all in understanding quantum mechanics4, quantum mechanics might be held, with at least some plausibility, to provide a context in which the dispositional theory appears more acceptable.
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