Benacerraf and Set-Theoretic Reductionist Realism

The paper is devoted to analysis of P. Benacerraf’s argument against set-theoretic reductionist realism which is a fragment of a broader argument, know as the “identification problem”. The analyzed fragment of P. Benacerraf’s argument concerns the possibility of reducing of mathematical notions to set-theoretic notions. The paper presents a reconstruction of P. Benacerraf’s original argumentation, its analysis and also several possible objections proposed by P. Benacerraf himself about 30 years later after the original publication. Namely, he claimed (1) that a set-theoretic definition of natural numbers in G. Frege’s fashion can serve as a proper and unique set-theoretic definition, (2) that his argument doesn’t undermine eliminative reductionsts’ position, (3) that even if there are no argument possible in favor of some particular set-theoretic definition of natural numbers one may take set-theoretic realism for granted. An analysis of the mentioned possible objections shows their dependence on a number of additional premises. The paper demonstrates that P. Benacerraf’s objections on his own argument against set-theoretic realism either have a pragmatic character themselves or essentially rely on additional arguments that are justified pragmatically or require additional argumentation. For example, his possible objections require that set theory is considered as the only true foundational theory in mathematics, and that it has several important pragmatic virtues, like convenience of use to formalize other mathematical theories. In some cases, P. Benacerraf’s objections on their own, or the indicated additional principles may well be called into question, which demonstrates the insufficiency of P. Benacerraf’s objections against his original argument. Without the mentioned pragmatic arguments P. Benacerraf’s objections become a kind of belief in mysticism. Accordingly, his doubts about his own argument against set-theoretical realism seem insufficient to reject the problem of identification and save the position of set-theoretical realism from collapse.