Two caveats are appropriate here. First, it is important to emphasize that these scholars differed in crucial ways about the philosophy of science. Barbour’s point here is to stress what is shared by them and to represent it in a simplified but instructive model (Figure 1C). Secondly, it is also important to recognize that many of these ideas had been discussed previously. Hempel, for example, had underscored the influence of theory on observation. Still neither he, nor Popper for that matter, incorporated it in the fundamental ways that Kuhn and Lakatos did.