Science, and in particular the process of theory-change in science, formed the major inspiration for Karl Popper’s whole philosophy. Popper learned about the success of Einstein’s revolutionary new theory in 1919 (the same year in which his discontent with Marxism and Freudianism reached crisis-point), and Einstein ‘became a dominant influence on my thinking—in the long run perhaps the most important influence of all.’ Popper explained why.