Bachelard regarded the scientific changes that took place in the early twentieth century as the beginning of a new era, not only for science, but also for philosophy. For him, the theory of relativity and quantum mechanics had shown that a new philosophical ontology and a new epistemology were required. I show that the type of philosophy with which he was more closely associated, in particular that of Léon Brunschvicg, offered to him a crucial starting point. Brunschvicg never considered scientific objects as independent of the mind, and as a consequence questions such as the existence of particles independently of the mind, theory or apparatus, were absent from his philosophy, which was rather aimed at analyzing the mind critically, and above all historically. Bachelard accepted the fundamental ideas of Brunschvicg’s philosophy; however, his own reading of contemporary science enabled him to go beyond it, as shown by his emphasis on the social production of knowledge, and by his removal of the distinction between ideas and technologically produced objects of knowledge. For him, modern science teaches philosophy that knowledge is not a phenomenology but rather a ‘phenomenotechnique’. I argue that Bachelard’s view that philosophy ‘should follow science’ stems from moral considerations.