A lógica das entidades intencionais

Abstract

A feature of the distinction between extensionalism and intensionalism, which has been widely taken as a criterion to separate the two positions, is that within an extensionalist logic, substitution is possible salva veritate (that is, without thereby changing the truth-value of the statement concerned) with respect to identical instances of some basic logical form – and in an intensionalist logic it is not. The different logical forms with respect to which such substitution might take place accounts for some of the variety of different extensionalisms on offer in the current philosophical landscape. So our starting-point is Frege’s puzzle. This question is frequently accepted as one of the foundations of modern semantics. To explain why a true sentence of the form “a = b” can be informative, unlike a sentence of the form “a = a”, Frege introduced an entity standing between an expression and the object denoted (bezeichnet) by the expression. He named this entity Sinn (sense) and explained the informative character of the true “a=b”-shaped sentences by saying that ‘a’ and ‘b’ denote one and the same object but differ in expressing (ausdrücken) distinct senses. The problem, though, is that Frege never defined sense. The conception of senses as procedures that is developed here has much in common with a number of other accounts that represent meanings, also, as structured objects of various kinds, though not necessarily as procedures. In the modern literature, this idea goes back to Rudolph Carnap’s (1947) notion of intensional isomorphism. Church in (1954) constructs an example of expressions that are intensionally isomorphic according to Carnap’s definition (i.e., expressions that share the same structure and whose parts are necessarily equivalent), but which fail to satisfy the principle of substitutability. The problem Church tackled is made possible by Carnap’s principle of tolerance (which itself is plausible). We are free to introduce into a language syntactically simple expressions which denote the same intension in different ways and thus fail to be synonymous. Tichý’s objectualist take on ‘operation-processes’ may be seen in part as linguistic structures transposed into an objectual key; operations, procedures, structures are not fundamentally and inherently syntactic items, but fully-fledged, non-linguistic entities, namely, constructions.