### Single Idea 15507

#### [catalogued under 4. Formal Logic / F. Set Theory ST / 4. Axioms for Sets / a. Axioms for sets]

Full Idea

Set theory has its unofficial axioms, traditional remarks about the nature of classes. They are never argued, but are passed heedlessly from one author to another. One of these says that the classes are nowhere: they are outside space and time.

Gist of Idea

Set theory has some unofficial axioms, generalisations about how to understand it

Source

David Lewis (Parts of Classes [1991], 2.1)

Book Reference

Lewis,David: 'Parts of Classes' [Blackwell 1991], p.31

A Reaction

Why don't the people who write formal books on set theory ever say things like this?