Formulações da validade dedutiva clássica costumam recorrer explicitamente a modalidades: por exemplo, um argumento é classicamente dedutivamente válido se, e somente se, necessariamente se as premissas forem verdadeiras, a conclusão também é verdadeira. Não é possível abolir completamente esse apelo ao discurso modal, porque a lógica clássica é o domínio das possibilidades. Não obstante, pode-se, por intermédio de uma semântica informacional, evitar que o usuário da lógica clássica tenha de manipular modalidades, ainda que elas estejam, de algum modo, imbricadas nos (...) infons – unidades mínimas de informação. A partir do trabalho pioneiro de Carnap e de Bar-Hillel, apresentarei duas semânticas informacionais: uma delas diretamente relacionada a mundos possíveis, e a outra relacionada aos duais de mundos possíveis. (shrink)

In 1958, to refute the argument known as the theoretician's dilemma, Hempel suggested that theoretical terms might be logically indispensable for inductive systematization of observational statements. This thesis, in some form or another, has later been supported by Scheffler, Lehrer, and Tuomela, and opposed by Bohnert, Hooker, Stegmüller, and Cornman. In this paper, a critical survey of this discussion is given. Several different putative definitions of the crucial notion inductive systematization achieved by a theory are discussed by reference to the (...) properties of inductive inference. The consequences of the following differences between deductive and inductive inference are emphasized: the lack of simple transitivity properties (even in a modified sense) of inductive inference, and the failure of the inductive analogue of the converse of The Deduction Theorem. The main conclusions are: (i) Hempel's original thesis may very well be right but his argument for it is unsatisfactory, (ii) theoretical terms can be logically indispensable for a non-Hempelian kind of inductive systematization, relative to both Craigian and Ramseyan elimination, (iii) Lehrer's attempt to prove the indispensability of theoretical terms for inductive-probabilistic systematization is, as a modification of Hempelian kind of inductive-deterministic systematization, unsatisfactory, and (iv) there does not seem to be much hope of escaping the conclusion (ii), if it is true, by extending the Craigian replacement programme along the lines suggested by Cornman. (shrink)

Quine's reasons for recommending naturalist epistemology are: (1) knowledge, Mind and meaning are part of the world they have to do with, (2) since the cartesian quest for certainty and reductionism of carnap's 'aufbau' type have failed, Rational reconstruction has no more any advantage over psychology, (3) since phenomenalist validation of science is no longer our concern, It is not circular to appeal to psychology. Against this it is argued that (a) no definite methodological policy can be based on (1) (...) alone; (b) certainty and phenomenalist reduction are not the only purposes of rational reconstruction; (c) it would be circular to appeal to psychology in developing a theory of rational method of acquiring knowledge: (d) logic and psychology of science are complementary not mutually exclusive. (shrink)