 Church’s published remarks on set theory are scattered, relatively brief and stop short of full endorsement. However, his overall attitude towards set theory was accepting and conciliatory, although he was skeptical of some of its axioms, including separation and choice. His doctoral dissertation (under Veblen) was on “Alternatives to Zermelo’s Assumption” (1927)—namely, the axiom of choice. He viewed Zermelo’s axiomatization of set theory as “transferring” the concepts of class and class membership from the “(unformalized) logical level” to the “(formalized) mathematical level”, but viewed the improvements due to von Neumann, Fraenkel and Skolem as bringing it continually closer to (formalized) logic, so that