14 research outputs found
Complexity Classifications via Algebraic Logic
Complexity and decidability of logics is an active research area involving a wide range of different logical systems. We introduce an algebraic approach to complexity classifications of computational logics. Our base system GRA, or general relation algebra, is equiexpressive with first-order logic FO. It resembles cylindric algebra but employs a finite signature with only seven different operators, thus also giving a very succinct characterization of the expressive capacities of first-order logic. We provide a comprehensive classification of the decidability and complexity of the systems obtained by limiting the allowed sets of operators of GRA. We also discuss variants and extensions of GRA, and we provide algebraic characterizations of a range of well-known decidable logics
Algebraic classifications for fragments of first-order logic and beyond
Complexity and decidability of logics is a major research area involving a
huge range of different logical systems. This calls for a unified and
systematic approach for the field. We introduce a research program based on an
algebraic approach to complexity classifications of fragments of first-order
logic (FO) and beyond. Our base system GRA, or general relation algebra, is
equiexpressive with FO. It resembles cylindric algebra but employs a finite
signature with only seven different operators. We provide a comprehensive
classification of the decidability and complexity of the systems obtained by
limiting the allowed sets of operators. We also give algebraic
characterizations of the best known decidable fragments of FO. Furthermore, to
move beyond FO, we introduce the notion of a generalized operator and briefly
study related systems.Comment: Significantly updates the first version. The principal set of
operations change
Property Theories
Revised and reprinted; originally in Dov Gabbay & Franz Guenthner (eds.), Handbook of Philosophical Logic, Volume IV. Kluwer 133-251. -- Two sorts of property theory are distinguished, those dealing with intensional contexts property abstracts (infinitive and gerundive phrases) and proposition abstracts (âthatâ-clauses) and those dealing with predication (or instantiation) relations. The first is deemed to be epistemologically more primary, for âthe argument from intensional logicâ is perhaps the best argument for the existence of properties. This argument is presented in the course of discussing generality, quantifying-in, learnability, referential semantics, nominalism, conceptualism, realism, type-freedom, the first-order/higher-order controversy, names, indexicals, descriptions, Matesâ puzzle, and the paradox of analysis. Two first-order intensional logics are then formulated. Finally, fixed-point type-free theories of predication are discussed, especially their relation to the question whether properties may be identified with propositional functions