Varieties of propensity

The propensity interpretation of probability was introduced by Popper ([195 7]), but has subsequently been developed in different ways by quite a numbe r of philosophers of science. This paper does not attempt a complete survey , but discusses a number of different versions of the theory, thereby givin g some idea of the varieties of propensity. propensity. Propensity theories are classified into (i) long-run and (ii) single-case. The paper argues Fo r a long-run version of the propensity theory, but this is contrasted with two single-case propensity theories, one due to Miller and the later Popper , and the other to Fetter. The three approaches are compared by examining h ow they deal with a key problem for the propensity approach, namely the rel ationship between propensity and causality and Humphreys' paradox. 1 Introduction 2 Popper's first version of the propensity theory 3 Can there be objective probabilities of single events? 4 A classification of propensity theories 5 The propensity theories of Miller and the later Popper, and of Fetzer 6 Propensity and causality: Humphreys' paradox.