The "Theory" section misrepresents Sohn-Rethel's engagement with Kant, which, in
Intellectual and Manual Labour, at least, is a deeply critical one which employs Marxist historical materialism to dismantle and critique Kantian idelaism as rooted in exchange abstraction and a division between manual and intellectual labor. Sohn-Rethel doesn't fuse Marx and Kant as if both are on equal footing, but uses the former to critique and expose the latter
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