In his 1965 farewell lecture at Brandeis University, Herbert Marcuse read a long passage from the Grundrisse's "fragment on machines" and then observed: “But Marx himself has repressed this vision, which now appears as his most realistic, his most amazing insight!"
In Time, Labor and Social Domination, published 28 years later, Moishe Postone addressed the same section from the Grundrisse and commented:
These passages do not represent utopian visions that later were excluded from Marx's more "sober" analysis in Capital but are a key to understanding that analysis; they provide the point of departure for a reinterpretation of the basic categories of Marx' s mature critique that can overcome the limits of the traditional Marxist paradigm.
Who was right? Did Marx repress his most amazing insight or is that insight from the Grundrisse a key to interpreting Marx's analysis in Capital? I would argue that both Marcuse and Postone are partly right and partly wrong. Marx didn't so much repress his realistic, amazing insight from the Grundrisse in Capital as hide it under bushels of supplementary illustrative material. You can find it there if you are patient and know what to look for.
In that respect, passages from the Grundrisse are indeed a key to understanding and reinterpreting Capital. But what is the key to understanding and reinterpreting the Grundrisse? It is the 1821 pamphlet, The Source and Remedy of the Natural Difficulties, that Marx cited and quoted from repeatedly in the Grundrisse, that Engels claimed Marx had "rescued from its oblivion," that Marx was fascinated by in the notebooks published as Theories of Surplus Value, and that Postone, Marcuse and almost every other interpreter of Marx's thought has ignored.
I discussed this peculiar omission in an article published last year, "The Ambivalence of Disposable Time: The Source and Remedy of the National Difficulties at two hundred." In the last few weeks, I have completed a 21,000 word manuscript, "A shadow of things to come" that probes further into the backstory of the pamphlet and forward into the fate of disposable time in today's world. I'm sure it's not the sort of thing academic publishers would be interested in and thus am uncertain about how I will present my arguments to the public.