Single Idea 15511

[catalogued under 4. Formal Logic / F. Set Theory ST / 3. Types of Set / c. Unit (Singleton) Sets]

Full Idea

Suppose the relation of member to singleton is external. Why must Possum be a member of one singleton rather than another? Why isn't it contingent which singleton is his?


Possum was David Lewis's cat

Gist of Idea

If singleton membership is external, why is an object a member of one rather than another?


David Lewis (Parts of Classes [1991], 2.2)

Book Reference

Lewis,David: 'Parts of Classes' [Blackwell 1991], p.37

A Reaction

He cites Van Inwagen for raising this question, and answers it in terms of counterparts. So is the relation internal or external? I think of sets as pairs of curly brackets, not existing entities, so the question doesn't bother me.