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MODAL QUANTIFIERS, POTENTIAL INFINITY, AND YABLO SEQUENCES

Published online by Cambridge University Press:  17 March 2022

MICHAŁ TOMASZ GODZISZEWSKI*
Affiliation:
UNIVERSITY OF LODZ POLAND
RAFAŁ URBANIAK
Affiliation:
UNIVERSITY OF GDAŃSK POLAND E-mail: rfl.urbaniak@gmail.com

Abstract

When properly arithmetized, Yablo’s paradox results in a set of formulas which (with local disquotation in the background) turns out to be consistent, but $\omega $-inconsistent. Adding either uniform disquotation or the $\omega $-rule results in inconsistency. Since the paradox involves an infinite sequence of sentences, one might think that it doesn’t arise in finitary contexts. We study whether it does. It turns out that the issue depends on how the finitistic approach is formalized. On one of them, proposed by M. Mostowski, all the paradoxical sentences simply fail to hold. This happens at a price: the underlying finitistic arithmetic itself is $\omega $-inconsistent. Finally, when studied in the context of a finitistic approach which preserves the truth of standard arithmetic (developed by one of the authors), the paradox strikes back—it does so with double force, for now the inconsistency can be obtained without the use of uniform disquotation or the $\omega $-rule.

Information

Type
Research Article
Copyright
© The Author(s), 2022. Published by Cambridge University Press on behalf of The Association for Symbolic Logic

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