Publication details

The Rule of Existential Generalisation and Explicit Substitution

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Authors

RACLAVSKÝ Jiří

Year of publication 2022
Type Article in Periodical
Magazine / Source Logic and logical philosophy
MU Faculty or unit

Faculty of Arts

Citation
Web https://apcz.umk.pl/LLP/article/view/31855/30016
Doi http://dx.doi.org/10.12775/LLP.2021.011
Keywords existential generalisation; quantifying in; explicit substitution; hyperintensional logic; natural deduction
Description The present paper offers the rule of existential generalisation (EG) that is uniformly applicable within extensional, intensional and hyperintensional contexts. In contradistinction to Quine and his followers, quantification into various modal contexts and some belief attitudes is possible without obstacles. The hyperintensional logic deployed in this paper incorporates explicit substitution and so the rule (EG) is fully specified inside the logic. The logic is equipped with a natural deduction system within which (EG) is derived from its rules for the existential quantifier, substitution and functional application. This shows that (EG) is not primitive, as often assumed even in advanced writings on natural deduction. Arguments involving existential generalisation are shown to be valid if the sequents containing their premises and conclusions are derivable using the rule (EG). The invalidity of arguments seemingly employing (EG) is explained with recourse to the definition of substitution.
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