structure for 'Formal Logic'    |     alphabetical list of themes    |     expand these ideas

4. Formal Logic / F. Set Theory ST / 7. Natural Sets

[which sets are natural, rather than conventional]

9 ideas
What physical facts could underlie 0 or 1, or very large numbers? [Frege on Mill]
Russell's proposal was that only meaningful predicates have sets as their extensions [Orenstein on Russell]
A class is natural when everybody can spot further members of it [Quinton]
We can have a series with identical members [Tait]
Zermelo allows ur-elements, to enable the widespread application of set-theory [Hallett,M]
Maddy replaces pure sets with just objects and perceived sets of objects [Shapiro on Maddy]
The master science is physical objects divided into sets [Maddy]
ZFU refers to the physical world, when it talks of 'urelements' [Chihara]
A flock of birds is not a set, because a set cannot go anywhere [Brown,JR]