A decision on the scope of the philosophy of science is a precondition for writing about its history. Unfortunately, philosophers and scientists are not in agreement on the nature of the philosophy of science. Even practising philosophers of science often disagree about the proper subject-matter of their discipline. An example of this lack of agreement is the exchange between Stephen Toulmin and Ernest Nagel on whether philosophy of science should be a study of scientific achievement in vivo, or a study of problems of explanation and confirmation as reformulated in the terms of deductive logic.1 To establish a basis for the subsequent historical survey, it will be helpful to sketch four viewpoints on the philosophy of science.