 While Popper (1957) is often credited as being the pioneer of propensity interpretations, we already find the key idea in the writings of Peirce (1910, 79–80): “I am, then, to define the meaning of the statement that the probability, that if a die be thrown from a dice box it will turn up a number divisible by three, is one-third. The statement means that the die has a certain ‘would-be’; and to say that the die has a ‘would-be’ is to say that it has a property, quite analogous to any habit that a man might have.” A man’s habit is a paradigmatic example of a disposition; according to Peirce the die’s probability of landing 3 or 6 is an analogous disposition. We might think of various habits coming in different degrees, measuring their various strengths. Analogously, the die’s propensities to land various ways measure the strength of its dispositions to do so. 