Full Idea
In conjunction with Extensionality, Pairing entails that given a single non-set, infinitely many sets exist.
Gist of Idea
Pairing (with Extensionality) guarantees an infinity of sets, just from a single element
Source
Gideon Rosen (The Limits of Contingency [2006], 04)
Book Reference
'Identity and Modality', ed/tr. MacBride,Fraser [OUP 2006], p.18