Abstract: The concept of “effectivity” traverses the texts of Louis Althusser. It has the strict and precise theoretical function that generally a concept should have,and it expresses the materialist implication of Althusser's philosophy. In the Marxist context,the emphasis of effectivity means that we should not only admit the economic base as a determinant factor,but also recognize the relatively independent effectivity of superstructures. In Althusser's opinion,the distinction between “overdetermination” and Hegelian simple contradiction resides exactly in the fact that the former should be considered as a complex system of effectivity. It is only from the perspective of effectivity that we can understand how ideology functions as ideas in the process of regeneration,and in what sense ideology is of materiality:not “that which is material is effective”,but “that which is effective is material”. With the help of Spinozism,Althusser has affirmed the materiality of ideology based on the conception of efficacy,which thus can be seen as deepening and development of historical materialism.

Key words: Althusser, effectivity, materialism, ideology, Spinoza