Full Idea
Axiomatising set theory leads to a relativity of set-theoretic notions, and this relativity is inseparably bound up with every thoroughgoing axiomatisation.
Gist of Idea
Axiomatising set theory makes it all relative
Source
Thoralf Skolem (Remarks on axiomatised set theory [1922], p.296)
Book Reference
'From Frege to Gödel 1879-1931', ed/tr. Heijenoort,Jean van [Harvard 1967], p.296