Full Idea
The Axiom of Foundation (Zermelo 1930) says 'Every (descending) chain in which each element is a member of the previous one is of finite length'. ..This forbids circles of membership, or ungrounded sets. ..The iterative conception gives this centre stage.
Gist of Idea
Foundation says descending chains are of finite length, blocking circularity, or ungrounded sets
Source
Shaughan Lavine (Understanding the Infinite [1994], V.4)
Book Reference
Lavine,Shaughan: 'Understanding the Infinite' [Harvard 1994], p.135