The necessity of contingency
Rereading Althusser on structural causality
Among the concepts proposed by Althusser in the course of his famous symptomatic reading of Marx’s Capital, structural causality plays a central role. Extrapolated from Marx’s writings via a detour through the philosophy of Spinoza, it came to represent the concept in which Althusser summed up ‘Marx’s immense theoretical revolution’.  As is well known, for Althusser, by breaking with the other two models of causality available in Marx’s time (the mechanistic causality derived from Descartes and the ‘expressive’ causality derived from Leibniz and above all Hegel), ‘structural causality’ made it possible for the first time to think of history as a process deprived of any essence and telos, without subject and without end – or, as Althusser puts it in another formulation, as a ‘structure of structures’ without any centre.  It was, therefore, the concept that condensed the anti-humanist reading produced in the 1960s by Althusser and his collaborators, one that soon became famous under the label ‘structural Marxism’.
If the centrality of structural causality to the overall project of recasting Marxism is beyond doubt, the fate of this concept is curious. For one thing, the number of pages devoted to the explicit theoretical elaboration of structural causality in Reading Capital is rather few (fourteen in the French edition). More importantly, the concept will soon disappear from Althusser’s discourse, in his attempt to correct his so-called ‘theoreticism’ and to reject the allegations of ‘structuralism’, to which ‘structural causality’ evidently gave rise through its name. It is well known that structural causality was one of the concepts that led to fierce criticism of Althusser. For his proximity to structuralism, he was accused of denying history; for his reliance on Spinoza, he was accused of endorsing a metaphysical concept of necessity that did not leave any space for freedom or – more importantly for the purposes of this article – for contingency. Famously (to limit ourselves to the anglophone reception), Althusser was attacked by the British Marxist E.P. Thompson, who accused him of endorsing a deterministic philosophy of history that asserted the timeless reproduction of the structure of a certain mode of production.  The same type of critique was put forward, first, by Hindess and Hirst, and then by Laclau and Mouffe, in their Hegemony and Socialist Strategy. There, the latter authors argued that the most vital part of Althusser’s project is to be found in his concept of ‘overdetermination’, but that soon after the essay (dating from 1962) in which that concept was propounded, Althusser retreated towards a hopeless metaphysical rationalism that culminated in the concept of structural causality. In their reading, Althusser’s attempt to pass from Hegel to Spinoza in his reading of Marx only resulted in the substitution of a strictly logico-mathematical necessity for a teleological necessity governing history.  In his now-classical study on Western Marxism, Perry Anderson remarked that Althusser’s Spinozism was so deep that the metaphysical determinism of Spinoza could be found without any modification, in particular in the ‘implacable logic’, as he called it, of ‘structural causality’.  As Peter Thomas has recently noted, Anderson’s study of the relationship between Althusser and Spinoza was seminal: most later interpretations of Althusser’s Marxism merely repeating Anderson’s reading without any modification. 
In this article, I argue that Althusser’s concept of structural causality cannot be reduced to a metaphysical necessitarianism of Spinoza’s kind or a structuralist determinism. My aim is to show that, far from being a strictly determinist concept, structural causality was the concept through which Althusser attempted for the first time to develop a logic capable of including contingency as a structural dimension, and that, far from asserting the timeless reproduction of the structure (i.e. of a certain mode of production), it should be read as the concept through which Althusser tried to propose a non-dialectical theory of structural change.
Now, it is well known today, after the publication of Althusser’s late writings, that he proposed in the 1980s a new philosophy for Marxism that he named materialism of ‘the encounter’ or of ‘the swerve’.