‘Abduction’ was the term Charles Sanders Peirce used in his later writings for a type of inference that he had earlier called ‘hypothesis’ and that is now commonly called ‘inference to the best explanation’. According to Peirce, abduction constituted, alongside induction, a distinct second form of nondemonstrative or probabilistic inference. Especially in his later work, Peirce conceived of abd...

This paper adds comparative adjectives to the known systems of syllogistic logic. The comparatives are interpreted by transitive and irreflexive relations. The main point is to obtain sound and complete axiomatizations of the logics.

Previous research has demonstrated working memory and executive deficits in recreational users of MDMA (3,4-methylenedioxymethamphetamine; Ecstasy). In turn, both of these constructs have been implicated in syllogistic reasoning performance. Twenty-two MDMA users (mean age = 21.36) and 26 MDMA nonuser controls (mean age = 21.31) were tested on syllogisms of varying difficulty and on measures of...

For a cognitive account of reasoning it is useful to factor out the syntactic aspect — the aspect that has to do with pattern matching and simple substitution — from the rest. The calculus of monotonicity, alias the calculus of natural logic, does precisely this, for it is a calculus of appropriate substitutions at marked positions in syntactic structures. We first introduce the semantic and th...

A key question for cognitive theories of reasoning is whether logical reasoning is inherently a sentential linguistic process or a process requiring spatial manipulation and search. We addressed this question in an event-related fMRI study of syllogistic reasoning, using sentences with and without semantic content. Our findings indicate involvement of two dissociable networks in deductive reaso...