Full Idea
In Set Theory, the primitive name of Being is the void, the empty set. The whole hierarchy takes root in it. In a certain sense, it alone 'is'.
Gist of Idea
The primitive name of Being is the empty set; in a sense, only the empty set 'is'
Source
Alain Badiou (Briefings on Existence [1998], 6)
Book Reference
Badiou,Alain: 'Briefings on Existence', ed/tr. Madarsz,Norman [SUNY 2006], p.98
A Reaction
This is the key to Badiou's view that ontology is mathematics. David Lewis pursued interesting enquiries in this area.