Originally Posted by

**Hartlw** Start to list all sets starting with A,B,C,

you cant get past A:

A, {A},{{A}}, {{{A}}},
..

Let alone A, B:

A, B, {A,B}, {A,{A,B}}, {B,{A,B}}, {A, {A,{A,B}}}, {A, {B,{A,B}}},

{B,{A,{A,B}}}, {B,{B,{A,B}}},
..

True, the fact that you cant list them all doesnt mean they dont exist. However, it appears to me this construction renders the notion of all sets meaningless, especially if you start with A any object or concept in the universe. It's not mathematics anymore, its just words and combinations of words- philosophy (in my opinion).

And each one of these sets has a different definiton that have to be combined.