I have described François Laruelle’s non-philosophy as a particular variant of post-Althusserian thought maintaining intact key Althusserian notions such as the distinction between the real object and the theoretical object, and determination in the last instance.
Graham Harman’s OOO is similarly a de-scientised and de-Marxed variant of the post-Althusserian problematic: https://terenceblake.wordpress.com/2012/07/22/withdrawal-is-abstraction-harmans-ooo-althusser-unmarxed/
One is entitled to ask: what corresponds to the Althusserian notion of “determination in the last instance” in the OOO problematic? The answer is “withdrawal”.
OOO’s doctrine of the real object corresponds to what Zizek in DISPARITIES calls “full objectivization”. For Harman what really exists in the last instance is the real object, the rest is “sensual”, mere sham, illusion.
Zizek deploys the notion of “overdetermination” to resist the homogenization imposed by doctrines of withdrawal or of determination in the last instance (the last instance never comes). A fully withdrawn object can never be subject, it is brute substance, a pure posit of the non-dialectical imagination.
It would be a mistake to suppose that Harman’s incoherent system could be saved by the introduction of a more or less robust notion of causality. Harman’s strict OOP perspective rules out the unification of the real that the category of causation would impose.
On Harman’s view objects withdraw from each other, objects withdraw from all relation including the causal relation. Other variants of OOO, such as Levi Bryant’s naturalised construal of objects, tried valiantly but incoherently to re-inject causality and capacity into the OOO system. However, Bryant ultimately saw the futility and the impossibility of such a hybrid and gave up the title of OOO altogether.
Note: I am indebted to a discussion with David Morey for helping me to clarify this last point.