In what does the sense of a sentential connective consist? Like many others, I hold that its sense lies in rules that govern deductions. In the present paper, however, I argue that a classical logician should take the relevant deductions to be arguments involving affirmative or negative answers to yes-or-no questions that contain the connective. An intuitionistic logician will differ in concentrating exclusively upon affirmative answers. I conclude by arguing that a well known intuitionistic criticism of classical logic fails if (...) the answer "No" is accorded parity with the answer "Yes". (shrink)

The main result of this paper is a normalizing system of natural deduction for the full language of intuitionistic linear logic. No explicit weakening or contraction rules for -formulas are needed. By the systematic use of general elimination rules a correspondence between normal derivations and cut-free derivations in sequent calculus is obtained. Normalization and the subformula property for normal derivations follow through translation to sequent calculus and cut-elimination.

Extensions of Natural Deduction to Substructural Logics of Intuitionistic Logic are shown: Fragments of Intuitionistic Linear, Relevant and BCK Logic. Rules for implication, conjunction, disjunction and falsum are defined, where conjunction and disjunction respect contexts of assumptions. So, conjunction and disjunction are additive in the terminology of linear logic. Explicit contraction and weakening rules are given. It is shown that conversions and permutations can be adapted to all these rules, and that weak normalisation and subformula property holds. The results generalise (...) to quantification. (shrink)

We give two proofs of strong normalisation for second order classical natural deduction. The first one is an adaptation of the method of reducibility candidates introduced in [9] for second order intuitionistic natural deduction; the extension to the classical case requires in particular a simplification of the notion of reducibility candidate. The second one is a reduction to the intuitionistic case, using a Kolmogorov translation.