In his magnum opus Being and Event, Alain Badiou identifies ontology with mathematics and uses a mathematical formalization of ontological discourse to generate an account of extra-ontological 'truth-events'. Informed by deconstructive critiques of the metaphysical ontologies of presence, Badiou establishes an anti-phenomenological conception of ontological presentation. Presentation's internal structure is that of an anti-phenomenon: presence's necessarily empty and insubstantial contrary. But the result is that Being and Event is riven by a fundamental methodological idealism. Badiou cannot secure the connection he wishes to establish between the formal discursive structure of mathematical ontology and extra-discursive reality. The decisive link between being and event, i.e. between Badiou's purely formal conception of ontological presentation and the extra-ontological reality of the event, is precluded by the very structure of the concept of presentation which is central to Badiou's argument.