 Salmon’s hope to have solved the problem left open by Reichenbach’s argument for the justification of inductive methods was soon disappointed, especially after the criticism raised by Ian Hacking (1965 and 1968). Hacking showed that the three conditions of consistency, symmetry and invariance taken together are necessary and sufficient to select the rule of induction among the class of asymptotic rules. Hacking’s consistency and invariant conditions are stronger versions of Salmon’s requirements of regularity and linguistic invariance, while the symmetry condition (corresponding to the property usually called exchangeability) requires that for any given value of the relative frequency observed in a sample, the posited value of the limiting frequency must be insensitive to the order in which the items of the sample were observed to occur. This requirement is commonly accepted by the upholders of the subjective interpretation of probability, but for a frequentist like Salmon, who held that the evaluation of probability must be entirely based on empirical data, symmetry (exchangeability) can only mean a factual assumption on the nature of the population under study. This clashes with a justification in tune with Reichenbach’s perspective. As Salmon observed, Reichenbach’s rule of induction