The harmony of the unexpected

This study of the epistemological thought of Henri Poincar (1854-1912) has a dual aim: firstly, to identify and analyze the main sources of inspiration for his epistemological reflections on physics; secondly, to analyze the content of these reflections as they relate to the method, evolution and structure of physical theories. They reveal thematic commitments favoring theoretical pluralism, criticism of ontological assumptions and the role of regulating principles and analogies. They are particularly illuminating for the stage in the history of physics that corresponds to what Poincar calls the physics of principles.