In order to illuminate a French musical identity of the 1920s achieved via foreign influence, my article examines two subtle transformations: on the one hand between Ravel’s ‘theory’ of early jazz-blues and the actualities of early jazz, already partially Gallicized and classicized; and on the other between Ravel’s theory (of transformation) and his practice in the Violin Sonata. His ‘Blues’ gives as much as it takes, catalyzing his late music, yet also anticipating popular developments of the 1930s, in France and abroad.