My thesis is simple, Graham Harman’s metaphysics is incoherent. It does not survive even the simplest examination. In fact Harman has several different metaphysics confounded together in his presentations. The prime metaphysics is based on real withdrawn objects. “Objects withdraw from relation”, declares Harman’s SR/OOO Tutorial. There is no room for the “fourfold” in such a metaphysics, and in fact the fourfold constitutes a second metaphysics blithely conflated with the first. Next, various epicycles are needed to get round various rather evident problems, and “vicarious causation” is one such epicycle, having no motivation other than to resolve the initial incoherence.
“Objects withdraw from relation” is often conflated with a quite different thesis “objects withdraw from each other”. The notion of absolute withdrawal is deeply incoherent, but even when approached superficially it is too inflexible. Worries arise that “withdrawal” itself is a relation, and that objects should then be said to withdraw from withdrawal. A related problem is the conclusion that an object withdraws from itself, which seems to imply not only the absence of self-accessibility but also of self-identity. To put a stop to such vicious circles the notion of weak or partial withdrawal needed to be developped.This is in effect the position advocated by Levi Bryant, and also by Jon Cogburn.
Note: I have written quite a lot on these incoherences, much of which is collected here.