  First, the claim that ‘evidence is prior to theory’ might suggest a simple model of scientific method that is often associated (whether fairly or unfairly) with Francis Bacon. According to the model in question, the collection of evidence is temporally prior to the formulation of any theory or theories of the relevant domain. That is, the first stage in any properly-conducted scientific inquiry consists in gathering and classifying a large amount of data; crucially, this process is in no way guided or aided by considerations of theory. Only after a large amount of data has been gathered and classified does the scientist first attempt to formulate some theory or theories of the domain in question. On this model, then, evidence is prior to theory within the context of discovery. This model—which Hempel (1966) dubbed ‘the narrow inductivist account of scientific inquiry’—is now universally rejected by philosophers. For it is now appreciated that, at any given time, which theories are accepted—or more weakly, which theories are taken to be plausible hypotheses—typically plays a crucial role in guiding the subsequent search for evidence which bears on those theories. Thus, a crucial experiment might be performed to decide between two rival theories T1 and T2; once performed, the outcome of that experiment constitutes an expansion in the total evidence which is subsequently available to the relevant scientific community. If, however, the two leading contenders had been theories T1 and T3, a different crucial experiment would have been performed, which would have (typically) resulted in a different expansion in the total evidence. The point that the formulation of hypotheses is often temporally prior to the collection of evidence which bears on their truth (and that this priority is no accident) is perhaps most immediately apparent on Popper's falsificationist model of science (1959), according to which exemplary scientific practice consists in repeatedly attempting to falsify whichever theory is presently most favored by the relevant scientific community. But it is no less true on other, less radical models of science, which (unlike Popper's) allow a role for confirming evidence as well as disconfirming evidence. As Hempel puts the point,