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Angel's Symmetry Thesis

In a recent discussion article [1], R. B. Angel argues against a purported "irrational" trend in a current philosophy of science. Specifically he argues for the symmetry of the logic of explanation and prediction, the "symmetry thesis," and contends that the arguments of Hanson, Scriven et al. against this thesis represent a "retrograde" movement. Angel attempts to meet these arguments by replying first to Hanson's article, [2], and second to a persistent counterexample to the symmetry thesis. I shall argue that Angel's reply to the latter is unsatisfactory. Proponents of the counterexample claim that accidental, inductive generalizations serve as predictive bases (i.e. when complimented by appropriate antecedent conditions a predictive base yields a prediction). However given the antecedent conditions, no inductive generalization which is merely accidental explains a particular fact. E.g. 'All ravens are black' and 'Jones is a raven' warrant the prediction that 'Jones is black'; but, if the generalization is merely accidental, they do not explain 'Jones is black.' Clearly the counterexample presupposes two views: