Is there an axiomatisation of some kind of category theory and a definition of sets in this framework such that the axioms of ZF resp. ZFC are theorems?

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    $\begingroup$ If you formulate everything correctly, ECTS + separation is equivalent to ZFC. There is a translation you need to do because ECTS is two-sorted. See Tom Leinster's nice summary article: arxiv.org/abs/1212.6543 $\endgroup$ Jan 20, 2019 at 12:33
  • $\begingroup$ Thanks for the reference. $\endgroup$ Jan 20, 2019 at 12:48
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    $\begingroup$ I think I meant replacement, not separation. It's whatever Leinster calls axiom 11. $\endgroup$ Jan 20, 2019 at 13:19

1 Answer 1


Yes, this is a well-known fact that goes back to Cole, Mitchell, and Osius in the 70's. The relevant kind of category is, as Harry says in the comments, a well-pointed topos with extra properties; Lawvere's Elementary Theory of the Category of Sets is an axiomatization of such a category. To define ZF-sets in such a category you build them along with their hereditary membership structure as well-founded graphs; there is a good introduction in Chapter VI of Mac Lane & Moerdijk's book Sheaves in Geometry and Logic. If you want a very detailed treatment that includes analogous results for a wide variety of set theories including both ZF and ZFC and also weaker and constructive versions, there is my own paper Comparing material and structural set theories.

  • $\begingroup$ You linked the v2 not the v3 of your paper. Was that intentional $\endgroup$ Jan 20, 2019 at 15:35
  • $\begingroup$ Thanks, i will use the references. $\endgroup$ Jan 20, 2019 at 16:47
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    $\begingroup$ @HarryGindi Yes, the two versions are identical, but v2 has the more permissive license. (-:O $\endgroup$ Jan 20, 2019 at 16:53

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