Against an established but substantially mistaken consensus, this intellectual biography suggests that a contextually informed reading of Sorel's work invalidates both the supposedly 'irrationalist' character of his theoretical elaboration and the interpretation of his syndicalism as a theory of insurrection for insurrections' sake.This is done by showing that Sorel's understanding of historical materialism was decisively shaped by epistemological questions on science, determinism, and freedom that characterized the French philosophical debate in the 1880s and 1890s. The inability of the dominant understanding of science to make room for human agency in history brought Sorel to remove both historical and economic determinism from his revision of Marxism and led him, through his readings of Vico and Labriola, to understand the social world in terms of collective agency embedded in changing institutions rather than as a set of phenomena connected by deterministic causal relations. This resulted in an understanding of the socialist transformation as a longue durée process of proletarian institutional evolution and led Sorel to see in existing proletarian institutions, most notably unions, the seeds of the society of tomorrow.As Sorel, after 1900, focussed on the more empirical question of how to ensure the progress of existing working class institutions, he became aware of living in an era characterized by a process of assimilation of European working classes into national frameworks. He understood, like Bernstein, that the increasing interdependency between national states and capital hampered the revolutionary potential of proletarian institutions. Unlike Bernstein, however, he refused to abandon the revolutionary ambitions that he thought were essential to Marxism. Thus, he dedicated his most important works, most notably the Reflections on violence, to the questions of class identity and class formation.Instead of the 'pessimist moaning for blood' described by G.D.H. Cole, Sorel emerges, philosophically, as an epistemologist concerned with human agency and with its essential historicity, and historically, as a Marxist who perceptively understood the challenges that a changing capitalism posed to the revolutionary perspective outlined by Marx.