“Those who suppose they are producing a materialist theory of knowledge when they make knowledge a passive recording and abandon the “active aspect” of knowledge to idealism, as Marx complains in the theses on Feuerbach, forget that all knowledge, and in particular all knowledge of the social world, is an act of construction implementing schemes of thought and expression, and that between conditions of existence and practices or representations there intervenes the structuring activity of the agents, who, far from reacting mechanically to mechanical stimulations, respond to the invitations or threats of a world whose meaning they have helped to produce.”