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Published online by Cambridge University Press: 14 March 2022
This paper draws its title from the recent symposium of which it was part; it attempts to respond to the question raised by that title, taking current work in set theory into account. To this end the paper contrasts set theory with number theory, examines a severe brand of set-theoretic realism that is suggested by a passage from Gödel, and sketches a first-order way of looking at the results about competing extensions of Zermelo-Fraenkel set theory. A formalistic sentiment may be detectable in some portions of the paper.
This is the text of a paper read at a joint symposium of the Association for Symbolic Logic and the American Philosophical Association on 27 December, 1967, in Boston. The paper bears the symposium's title; the other symposiasts were Donald A. Martin and Saul Kripke. I am very greatly indebted to B. S. Dreben, H. Putnam, and W. V. Quine, each of whom was a rich and generous source of insight and stimulation for me. But this is not to accuse any of them of sympathy with my position.