June 22, 2018:
It's difficult to draw conclusions about Althusser's final works. In part because we're still coming to understand them — and finding, to our surprise, that their results were present all along, a "subterranean current", as Althusser would say, within his own writings. I'll highlight the implications which seem most urgent to me.
First, Althusser demonstrated that in his maturity Marx held two incompatible conceptions of history simultaneously, without being aware of that fact or of their incompatibility. On the one hand, the simple binary dialectic of the contradiction of the productive forces with the relations of production; on the other hand class struggle. Of course, we actually knew this all along in a somewhat unconscious or anyway unformulated way: Althusser was clearly hostile from the beginning to the Hegelianism of the Preface to A Contribution to the Critique of Political Economy. When he says out loud that Marx never resolved this conflict, it's like a slap in the head: this explains the right wing and left wing interpretations of Marxism from the Second International onward.
His demonstration that Marxism lacks a comprehensive theory of the state — elements, but no theory ‐ is more detailed and better elaborated in On the Reproduction of Capitalism. This seems to me to be crucial from an activist perspective. I don't think we can have fully coherent movement strategies without it: there will always be lacunae which distort our practice. And, I think, we can probably now explain some of our own history.
But of course, Althusser's most radical move was the demotion of the idea of necessity in history, with its concomitant emphasis on chance. At first blush, this seems so alien to any of the Marxisms we've inherited, which all try in one way or another not only to explain what's happened but very importantly to predict what will happen based on rigorous analyses. Is this possible within an aleatory materialism?