Adorno coined the term ‘identitarianism’ in Negative Dialectics (1966), prompted by critique of Kantian and Hegelian philosophies.
The argument, very briefly, goes something like this. Like Hegel, Adorno rejected the manner of Kant’s distinction between noumenal and phenomenal forms. Put simply, Adorno granted Hegel’s claim concerning the historically- and conceptually-generative qualities of non-correspondence, but wanted to press Marx’s critique of philosophical idealism further against Hegelian Marxism. Adorno remains a dialectician. But, unlike Hegel and more like Marx, he eschewed the affirmative, synthetic moves of consciousness (ie., philosophical idealism) and accorded epistemological-historical priority to the object (matter, materialism) rather than the subject (idealism) in explaining the course of this generative, non-correspondence (or non-identity). Identitarianism and the idealist philosophies of Kant and Hegel are thereby contrasted to a materialist philosophy of non-correspondence, or what Adorno calls “negative dialectics.”
How it happened that ‘identitarianism’ came to be plausibly used as a synonym for ‘identity politics’—or, more accurately, co-opted by arch-identitarian Hegelian Marxists against any emphasis on race, gender and/or sexuality, and in their defense of more or less explicit arguments that class is the a priori or primary categorical division of substance—is a mystery to me.
There are a lot of criticisms to be made of Adorno. But I’m not sure what or who it serves to pretend he didn’t launch a massive assault on the elementary logical reasoning of Hegelian Marxism and Leninism.