The present paper offers the rule of existential generalization (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.
Pavel Materna proposed valuable explications of concept and conceptual system. After their introduction, we contrast conceptual systems with (a novel notion of) derivation systems. Derivation systems differ from conceptual systems especially in including derivation rules. This enables us to show close connections among the realms of objects, their concepts, and reasoning with concepts.
It is sometimes assumed that logico-semantical analysis of natural language consists in translation of natural language expressions into formal language ones. A moment reflection reveals that this translational thesis has unacceptable consequences. Firstly, to explain the meaning of the formal expression which is a translation of a natural language expression, one has to translate it into another language, thus an infinite regress of translations arises. Secondly, the translation does not disclose the meaning (it indicates only the sameness of meanings), which is a serious drawback because the semanticist's aim is to explicate meanings. In addition to a criticism of that translational thesis, I offer an alternative explanation of typical findings of semanticists (written juxtapositions of natural and formal expressions) which fits the idea that logico-semantical analysis of natural language should provide expression, meaning pairs.
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