Studia Logica

, 99:279

Contextual Deduction Theorems

Authors

    • School of Mathematical SciencesUniversity of KwaZulu-Natal (Westville Campus)
Article

DOI: 10.1007/s11225-011-9353-z

Cite this article as:
Raftery, J.G. Stud Logica (2011) 99: 279. doi:10.1007/s11225-011-9353-z

Abstract

Logics that do not have a deduction-detachment theorem (briefly, a DDT) may still possess a contextual DDT—a syntactic notion introduced here for arbitrary deductive systems, along with a local variant. Substructural logics without sentential constants are natural witnesses to these phenomena. In the presence of a contextual DDT, we can still upgrade many weak completeness results to strong ones, e.g., the finite model property implies the strong finite model property. It turns out that a finitary system has a contextual DDT iff it is protoalgebraic and gives rise to a dually Brouwerian semilattice of compact deductive filters in every finitely generated algebra of the corresponding type. Any such system is filter distributive, although it may lack the filter extension property. More generally, filter distributivity and modularity are characterized for all finitary systems with a local contextual DDT, and several examples are discussed. For algebraizable logics, the well-known correspondence between the DDT and the equational definability of principal congruences is adapted to the contextual case.

Keywords

Deductive system deduction-detachment theorem protoalgebraic algebraizable quasivariety EDPC distributive modular substructural logics

Copyright information

© Springer Science+Business Media B.V. 2011