POINCARÉ and Einstein based their conception of scientific discovery and invention as creative process on the "free choice" by thought of theoretical concepts and ideas. This "logical freedom" with respect to factual data is settled on the human critique of induction, on a refusal of pure empiricism, and on a conception of rational intelligibility indebted to Kant but combined at the same time with a critique of kantian apriorism. We emphasize the proximity of their convictions in this respect, despite differences in their philosophical ideas in other matters (Poincaré's conventionalism, Einstein's critical realism), and we compare this central feature of the two scientists-philosophers' epistemologies with others conceptions taken from thinkers of the past as well as contemporary to them. We consider also how this common interest and epistemological attitude had been made possible by the evolution of mathematics and physics in the immediately preceding period. We try to put these in connection with the processes of scientific invention as experienced by themselves in their creative innovations.
