Editing Axiom schema of specification (section)

== In Quine's New Foundations ==
{{Unreferenced section|date=June 2024}}
In the [[New Foundations]] approach to set theory pioneered by [[W. V. O. Quine]], the axiom of comprehension for a given predicate takes the unrestricted form, but the predicates that may be used in the schema are themselves restricted. The predicate ({{mvar|C}} is not in {{mvar|C}}) is forbidden, because the same symbol {{mvar|C}} appears on both sides of the membership symbol (and so at different "relative types"); thus, Russell's paradox is avoided. However, by taking {{math|{{var|P}}({{var|C}})}} to be {{math|1=({{var|C}} = {{var|C}})}}, which is allowed, we can form a set of all sets. For details, see [[stratification (mathematics)|stratification]].