Abstract

In recent literature there has been increased interest in the so-called “paradox of predictability” (PoP) which purportedly shows that a deterministic universe is fundamentally unpredictable, even if its initial state and governing laws are known perfectly. This ostensible conclusion has been used to support compatibilism, the thesis that determinism is compatible with free will: supposedly, the PoP reveals that the nature of determinism is misunderstood and actually allows freedom, hence also free will. The present paper aims to disprove this conclusion and show that the PoP has absolutely no implication concerning the predictability of deterministic systems and the nature of determinism. Its paradoxy arises from a confusion between mental and physical notions in its formulation (the PoP tacitly premises a mental arbiter with respect to whom notions such as prediction and signification have meaning) and disappears once it is expressed in purely physical language. Ultimately, the PoP demonstrates not that prediction is impossible under determinism, but merely the obvious fact that it is impossible to predict while simultaneously acting so as to disprove one’s own prediction. The related issue of the impossibility of self-prediction is also discussed.