Is it simple to be a Spinozist in philosophy?
Althusser and Deleuze
At strategic points in Reading Capital, Louis Althusser introduces Spinoza’s idea of an immanent cause as the decisive concept that is absent from Marx’s discourse.  For the Althusser of 1965, Spinoza’s model of causality is the great missing link in Marx’s thought, a philosophical omission and lacuna of symptomatic force. It explains the whole detour that Marx was forced to take through Hegel’s system of thought. Because Marx was neither aware of the concept of immanent causality in Spinoza nor produced it himself, the idea of the effectivity of structure is found only in practical state in the complexity with which Marx depicts the social reproduction of economic relations in Capital. According to Althusser, however, it appears there in false conceptual clothing, in borrowed language: in Hegelian terms of essence and appearance. This language belongs to a spiritual monism in which all differences are reduced, in a teleological circle, to transitional moments of the self-mediation of spirit.
With unexpected pathos, Althusser describes Spinoza as a marginal figure in the history of philosophy, a misunderstood, ‘repressed’, ‘subterranean’  voice in seventeenth-century metaphysics representing the sole witness not only to Marx’s immense scientific revolution in Capital, but also to Althusser’s own epistemological undertaking of removing from Marx’s philosophy all evolutionist, teleological and humanist elements in order to instigate a repoliticization of Marxism. Althusser finds in the anti-finalism of Spinoza’s philosophy the ‘greatest lesson in heresy that the world has seen’.  His philosophy allows him to conceptually specify Marx’s epistemological break and ascertain in the medium of this rupture how a dialectics that does not carry within itself the promise of its resolution can be linked to the renewal of communist politics in non-Stalinist orientation. Through the rejection of the beginning and the end, through the destruction of the onto-teleological ‘alliance between subject and goal’  and through an epistemology that includes imagination and error in the production of thought, Spinoza serves Althusser as a singular point of reference in order to uncover beneath Marx’s Hegelian terminology the scheme of a complex over- and underdetermination of social instances. In a paradoxical temporality that contracts centuries, Althusser finds in Spinoza the ‘only direct ancestor’  of Marx and his attempt to define society as complex structured whole, in which different instances of both base and superstructure interact with one another in their unequal relations and plural temporalities. 
With this forced interpretation, this epistemological act of violence, in which Marx is equipped with a non-Hegelian genealogy and, in an unnoticedly ideal way, reconciled with himself, Althusser stages in the mid-1960s a double overture. First, he introduces Spinoza into structural Marxism, to separate Marx’s economico-critical thought from Hegel’s speculative concept of totality and Feuerbach’s anthropological concept of alienation. He gives structuralism a causality model, in which the genesis of the real is no longer reduced to a mere recursion effect or a ‘combinatory’  of arbitrary elements (phonemes, kinship relations, etc.), but comprises politically significant moments of condensation and displacement. Second, Reading Capital forms the prelude to a wave of Spinoza receptions, in which seventeenth-century metaphysics is shifted far beyond Marxism into the radiant presence of structuralist philosophy. While after Husserl’s Paris lectures on the Meditations and Sartre’s publication of The Transcendence of the Ego, France experienced a phenomenological Descartes revival, Spinoza research remained, until the mid-1960s, a largely underdeveloped field.  In the course of a fulminant boost in reception in 1968 and 1969, in almost a single year, the studies of Martial Gueroult, Alexandre Matheron, Gilles Deleuze and Bernard Rousset were published.  Under the influence of Gueroult’s structural-genetic reading, they displayed an unprecedented systematic precision to position Spinoza’s thought against Descartes – particularly, against the doctrine of two substances, the depotentialization of nature, the use of the medieval concept of contingency and the idea of the incomprehensibility of a God of arbitrary decree implicated in the doctrine of the creation of the eternal truths. In comparison Althusser’s reading of Spinoza …