Which is to say that there is another kind of tradition lurking here. And like language, shared traditions make possible shared actions. They can take the tune places it hasn't been before. This is jazz. It is also historical materialism, which far predated postmodernism in understanding that human affairs were matters of cutting, pasting, and recombining.
History is made with materials provided by the past.
Socialism, for Marxists, was not a wish-list detailing every conceivable repair to be made to human society. It was a conjecture about what else might be possible in terms of social organization, given what capitalism had already brought forth. What Marxists and postmodernists ultimately disagree about is just how different a reorganization of the existing building blocks would be. And perhaps they're right. Perhaps whichever way we turn society, it will always come out the same.