Einstein was much engaged with philosophy. His publications on epistemological issues are numerous and some have proven to be important on their own account. Like many of the leading physicists that were his contemporaries – men such as Erwin Schrödinger and Max Planck – he saw engagement with the philosophy of science as part of the intellectual project of physics. Einstein was deeply involved with questions concerning, for example, how scientific creativity works and how abstract thought relates to the actual world.

In Einstein's case it is impossible to disentangle the philosopher from the physicist. Throughout his work there is an evident overlap of the two, as well as a clear interaction between them. As already suggested in the previous chapter, Einstein's physics determined his philosophical outlook, and his philosophy inspired the directions he took in physics. Thus, in striving for a coherent understanding of Einstein's later oeuvre, one needs to address the exchanges between his practices in theoretical physics and his expressed philosophical beliefs – even if the latter were not intended to constitute an elaborated and consistent system.

In this chapter we turn in more detail to Einstein's declared methodological positions. The most important source for these is his 10 June 1933 Herbert Spencer lecture at the University of Oxford, “On the Method of Theoretical Physics.” We will study the various ideas laid out in that lecture and try to see how they developed gradually in the years following the discovery of general relativity.