Abstract

In response to the growing number of paradoxes relating to the hypothesis of universal predictability, Sellars has written: … conceptual difficulties do arise about universal predictability if we fail to distinguish between what I shall call epistemic predictability and logical predictability. By epistemic predictability, I mean predictability by a predictor in the system. The concept of universal epistemic predictability does seem to be bound up with difficulties of the type explored by Gödel. By logical predictability, on the other hand, is meant that property of the process laws governing a physical system which involves the derivability of a description of the state of the system at a later time from a description of its state at an earlier time, without stipulating that the latter description be obtained by operations within the system. It can be argued, I believe, with considerable force that the latter is a misuse of the term ‘predictability’, but it does seem to me that this is what philosophers concerned with the free will and determinism issue have had in mind, and it simply muddies up the waters to harass these philosophers with Gödel problems about epistemic predictability.