Because of Marx's belief that the individual is a product of society, Althusser believes that it is pointless to try to build a social theory on a prior conception of the individual. The subject of observation is not individual human elements, but rather "structure". As he sees it, Marx does not explain society by appealing to the properties of individual persons—their beliefs, desires, preferences, and judgements. Rather, Marx defines society as a set of fixed "levels"^[37] and "practices".^[38] He uses this analysis to defend Marx's historical materialism against the charge that it crudely posits a base (economic level) and superstructure (culture/politics) "rising upon it" and then attempts to explain all aspects of the superstructure by appealing to features of the (economic) base (the well known architectural metaphor). For Althusser, it is a mistake to attribute this economic determinist view to Marx. In much the same way that he criticises the idea of a social theory founded on an historical conception of human needs, so does Althusser critique the idea thateconomic practice can be used in isolation to explain other aspects of society.^[39] Althusser believes that both the base and the superstructure are interdependent, although he keeps to the classic Marxist materialist understanding of the determination of the base "in the last instance" (albeit with some extension and revision). The advantage of levels and practices over individuals as a starting point is that although each practice is only a part of a complex whole of society, a practice is a whole in itself in that it consists of a number of different kinds of parts. Economic practice, for example, contains raw materials, tools, individual persons, etc., all united in a process of production.^[40]

Althusser conceives of society as an interconnected collection of these wholes: economic practice, ideological practice, and politico-legal practice. Although each practice has a degree of relative autonomy, together they make up one complex, structured whole (social formation).^[41] In his view, all levels and practices are dependent on each other. For example, amongst the relations of production of capitalist societies are the buying and selling of labour powerby capitalists and workers. These relations are part of economic practice, but can only exist within the context of a legal system which establishes individual agents as buyers and sellers; furthermore, the arrangement must be maintained by political and ideological means.^[42] From this it can be seen that aspects of economic practice depend on the superstructure and vice versa.^[43] For him this was the moment of reproduction and constituted the important role of the superstructure.