In what precise ways is philosophy instrumental in illuminating the genesis of the conceptual innovations wrought by a particular physical theory? In the first edition (1963) of this book and in some still earlier papers, I have used the unraveling of the history of the special theory of relativity to argue concretely that philosophy does have far-reaching relevance to the attainment of the following cardinal objectives of the historian of science: (i) the very posing of well-conceived, searching historical questions and (ii) the avoidance of serious historical blunders of certain kinds, and their discernment as such when they have been committed by those lacking the requisite philosophical mastery ([1], chap. 12; [2]). Specifically, I maintained in the context of the special theory of relativity that there is a symbiosis of the philosophy and the history of science as follows: no historically correct, let alone illuminating account of the development of that theory can be furnished without a prior rigorous comprehension of the philosophical conceptions underlying it and distinguishing it from its ancestors. At the same time, I recognized that the history of the theory, in its turn, may indeed contribute to the philosophical analysis of the theory by disclosing the vicissitudes in Einstein's own philosophical outlook.