One can get a very useful overview of the difference between Alain Badiou’s and Graham Harman’s philosophies by comparing the diagrammes of their philosophies (cf. Badiou’s diagramme and Harman’s diagramme).
There is a radical incompatibility between the two philosophies on a number of fundamental points
1) the object: there is a radical rupture in Harman’s scheme between the appearing sensual object and the withdrawn real object. For Badiou there is no such rupture, the appearing object is a multiple inside a world and the ontological object is a pure multiple. There is no barrier between them, both are real.
2) the subject: the subject for Badiou involves the whole diagramme. It exists in the emergence of a relation (of fidelity) to an emergence (of a Truth). As we saw in the last post, for Badiou emergence does not define a one-way movement as there is retroaction (both by directly and by indirect looping) of Truths on Being. Harman’s diagramme cuts the subject from the object via the veil of withdrawal, which is one-way only.
3) emergence vs withdrawal: Harman’s problem is that he cannot explain in the terms of his system how a withdrawn object can « de-withdraw ». The movement or trajectory of Badiou’s diagramme is horizontal, including thresholds of emergence. Objects, truths, and subjects are all immanent. The movement of Harman’s diagramme is vertical, including an epistemological and ontological barrier: the veil of unknowing/veil of withdrawal.
4) phenomenology: the place of phenomenological experience in Harman’s system is purely formal. Experience offers us sensual analoga of real objects, in particular it provides us with the basis for the intuition that the real is composed of objects (and relations). However, the veil of withdrawal voids all particular sensual objects, qualities, and relations of any ontological pertinence. There is no trajectory that can rise from sensual objects to real ones and no path, whether causal or deductive, leading from real objects to sensual ones.
The popularity (where it exists, as it is a very regional phenomenon) of Harman’s system is due to the intuition that OOO can be « flipped » into immanence, but that would involve subtracting some of Harman’s central assumptions (something that other OOO partisans have not hesitated to do).
Badiou claims that there are two modes of entry into his thought: (1) systematic, by means of the major treatises (including THEORY OF THE SUBJECT) and (2) phenomenological, by means of the manifestos and the trajectory embodied in the seminars. It would seem that the principle of « immanence » implies that the phenomenological trajectory has heuristic primacy, and includes multiple possible paths.
Note: I am indebted to a discussion with Chris Bateman for helping me to clarify these points.