Taken as a whole, this constitutes the Idea of Spinoza, and it is just what pure being was to the Eleatics (Vol. 1. pp. 244, 252). This Idea of Spino… - Benedictus de Spinoza

[Jérome Skalski's question: Wasn't Spinoza also a thinker of radical democracy? Philosophically, was Althusserian Marxism also a return to Spinoza?] Althusser admired the Spinoza of the Theological-Political Treatise, but that was not the aspect that interested him the most. You are absolutely right to say that Spinoza's thought is a radically democratic thought. This is a dimension that has come to the forefront for a while now, and which has been appropriated by a broad variety of philosophers some of whom effectively come from a Marxist background. However, this was not the aspect or dimension that interested Althusser. Not because he was hostile towards it, but because he fundamentally thought that radical democracy was a transition, an intermediary stage towards the dictatorship of the proletariat. From this point of view, he was a very orthodox Marxist. The dimension that he emphasized in Spinoza concerned the theory of ideology. With Spinoza, there is the first great materialist critique of ideology. Althusser defended a paradoxical thesis. I understand that it forcefully shocked many Marxists at the time but, on the other hand, it was very attractive to certain people among us. This idea was that the concept of ideology was the fundamental aspect of Marx's theoretical revolution: not only the critique of bourgeois ideology, but the critique of ideology in general. To Althusser, this also appeared to be an important point within the debates internal to Communism at the time, in that it was dominated by the ideological complex he called humanism and economism. He thought that the Marxist tradition was weak on the question of ideology and that Marx, even if he possessed the genius to invent the concept, had had a very bad analysis of it. In Spinoza, he found the elements for a materialist theory of ideology that was neither Feuerbachian or Hegelian, and was not attached to a philosophy of history or to the concept of an alienation of man or a human essence. All of this paired very well with what was called Althusser’s scientism, such as it was expressed in the idea of the epistemological break and led to his proximity with structuralism. Althusser quickly criticized these positions in his Elements of Self-Criticism.

Spinoza remained throughout his life, and well into the eighteenth century, a thinker whom one could admire only in secret, hiding one's sympathy just as his Marrano antecedents had concealed their wayward Jewishness. Open admiration could destroy even the most established of reputations, well into the eighteenth century's so-called Age of Reason. In the 1780s, for example, Friedrich Heinrich Jacobi launched a generalized attack on Enlightenment thought by claiming that the late poet Lessing had been a closet Spinozist, a charge sufficient to compromise the entire movement for which Lessing had been a leading spokesman. Jacobi even went after Immanuel Kant and his successors, arguing that "consistent philosophy is Spinozist, hence pantheist, fatalist, and atheist."

Every philosophy of philosophy that excludes Spinoza must be spurious. [Original in German: Jede Philosophie der Philosophie, nach der Spinosa kein Philosoph ist muß verdächtig scheinen.]