03/12 - Rodolfo Ertola

Adding connectives to non-classical logics

Already in 1919 Skolem studied, from an algebraic point of view, certain operations that appear afterwards from a logical point of view, for example in 1942 in a work by Moisil. This is done in the context of a logic that, more recently, has been called bi-intuitionistic. Some decades afterwards, there also appear many papers by the polish logician Rauszer on the same logic. More recently, in 2009, Priest gave a paraconsistent version of some kind of bi-intuitionistic logic. We have proved that, in fact, using a notion by Urbas, it is strictly paraconsistent. Approximately in the same tradition appears the connective ∆ of fuzzy logic. We have proved that, added to a Heyting algebra, the result is an equational class.

Another tradition was started in Russia by Novikov in the Fifties and corresponds to the notion of intuitionistic connective. These connectives are supposed to give conservative expansions and enjoy the Disjunction Property. Regarding this, we consider some problems that arise in the case of first-order intuitionistic logic for connectives suggested by Smetanich, Kuznetsov, Gabbay, and Humberstone.

Axioms may not be enough for the axiomatization, i.e. in some cases it is necessary to add a rule. From a semantical point of view, the choice is between a truth-preserving or a truth-degree-preserving consequence.

Unicamp - Brazil

19/11 - Esko Turunen, PhD*

A Paraconsistent Version of Pavelka's Fuzzy Logic

In 1979 Jan Pavelka introduced a very general framework to deal with many valued logics. Pavelka's  idea was to process Zadeh's Fuzzy Sets such that theories, rules of inference, proofs as well as  tautologies may be only partial, i.e. fuzzy. Pavelka defined all his concepts in complete residuated lattices. The main issue was to study the circumstances under which the fuzzy semantic consequence operation and fuzzy syntactic operation coincide; such a property is called Pavelka style completeness.  Pavelka solved the problem in the special case that the set of truth values is the Lukasiewicz sturucure, i.e. the real unit interval equipped with standard MV-structure. The present author has recently proved that Pavelka style completeness holds if, and only if the set of truth values is a complete MV-algebra. Thus, if in particular ,the set M of truth values is a certain collection of 2x2-matrices equipped with suitable operations, then M is a complete MV-algebra. In fact, the set M extends Belnap's four valued para consistent logic. Such an approach results a complete many-valued logic that behaves consistently when looking from outside: the structure in related to Lukasiewicz logic which is a consistent logic. However, looking the logic from inside, i.e. a single 2x2-matrix, para consistency steps in. Truth and falsehood are not opposites of each other, and also contradictions and lack of knowledge is involved.

*Tampere University of Technology (Tampere, Finland)

12/11 - Francesc Esteva* & Lluis Godo*

On paraconsistent fuzzy logics

Paraconsistent logics are specially tailored to deal with inconsistency, while fuzzy logics primarily deal with graded truth and vagueness. Aiming at studying logics that can handle inconsistency and graded truth at once, this talk will report about recent investigations on how a notion of paraconsistent fuzzy logic can be cast within the framework of the so-called logics of formal inconsistency (LFIs).

As in classical logic, it is clear that the notion of truth-preserving deduction commonly used in systems of mathematical fuzzy logic is incompatible with any form of paraconsistency. However, in the first part of the seminar we will show that, instead, some degree-preserving fuzzy logics exhibit interesting paraconsistency features. We will also consider expansions of these logics with additional negation connectives and study their paraconsistency properties as LFIs.

In the second part of the seminar, we will address a kind of converse problem, namely how to extend a given fuzzy logic with a new “consistency” operator in the style of the LFIs. We will introduce a set of postulates for this type of operators over the corresponding algebras, leading to the definition and axiomatization of a family of logics, expansions of MTL, whose degree-preserving counterpart are paraconsistent and moreover LFIs.

 

In the third and final part of the seminar, we will talk about some remarks on ongoing work on the study on intermediate paraconsistent fuzzy logics between the truth-preserving and degree-preserving logics.

 

*IIIA - CSIC, Barcelona, Spain

05/11 - Gabriele Pulcini

A Uniform Setting for Classical, Non-Monotonic and Paraconsistent Logic

In this talk, we propose a uniform syntactical framework encompassing classical, non monotonic and paraconsistent logic. Such a uniform framework is obtained by means of the control sets logical device. Control sets leave the underlying syntax unchanged, while affecting the very combinatorial structure of sequents and proofs. Moreover, we prove the cut-elimination theorem for a version of controlled propositional classical logic, i.e. the sequent calculus for classical propositional logic to which a control sets system is applied. Our goals are two-folds: i) to overcome the conceptual gap between classical and non-classical logics; ii) to give, in particular, a new (positive) account of paraconsistency (and non-monotonicity) in terms of concurrency.

22/10 - Rodrigo Freire

Funções de primeira ordem, Parte 2

Esta apresentação é dedicada às funções de primeira ordem, que são uma generalização das funções de verdade. Os conceitos de tabela de verdade e de sistema de funções de verdade, ambos introduzidos na lógica proposicional por Emil Post, são também generalizados e estudados no caso quantificacional. O tema central desta exposição é a relação de definição entre noções expressas por fórmulas da lógica de primeira ordem. Enfatizamos que a lógica não se ocupa apenas da relação de consequência entre noções expressas por fórmulas, em que uma noção é consequência de outras. A lógica também se ocupa da relação de definição entre noções, em que uma noção é definida a partir de outras. Em uma segunda parte, vamos analisar a relação de definição entre noções expressas por fórmulas da lógica de primeira ordem. Nós vemos a lógica de primeira ordem como uma estrutura matemática cujo domínio é o sistema de todas as funções e primeira ordem, munida das operações básicas e da relação de consequência entre funções de primeira ordem. Em particular, os domínios de subestruturas da lógica de primeira ordem são os sistemas de funções de primeira ordem.

01/10 - Rodrigo Freire

Funções de primeira ordem, Parte 1

Esta apresentação é dedicada às funções de primeira ordem, que são uma generalização das funções de verdade. Os conceitos de tabela de verdade e de sistema de funções de verdade, ambos introduzidos na lógica proposicional por Emil Post, são também generalizados e estudados no caso quantificacional. O tema central desta exposição é a relação de definição entre noções expressas por fórmulas da lógica de primeira ordem. Enfatizamos que a lógica não se ocupa apenas da relação de consequência entre noções expressas por fórmulas, em que uma noção é consequência de outras. A lógica também se ocupa da relação de definição entre noções, em que uma noção é definida a partir de outras. Em uma segunda parte, vamos analisar a relação de definição entre noções expressas por fórmulas da lógica de primeira ordem. Nós vemos a lógica de primeira ordem como uma estrutura matemática cujo domínio é o sistema de todas as funções e primeira ordem, munida das operações básicas e da relação de consequência entre funções de primeira ordem. Em particular, os domínios de subestruturas da lógica de primeira ordem são os sistemas de funções de primeira ordem.

24/09 - Mathieu Beirlaen*

Inconsistency-adaptive dialogical logic, or how to dialogue sensibly in the presence of inconsistencies

Even when inconsistencies are present, we can sensibly distinguish between good and bad arguments relying on these premises. Not anything goes: the mere presence of inconsistencies does not warrant the inference to any conclusion whatsoever. In order to separate good and bad inferences in the possible presence of inconsistency, we nowadays have a wide range of paraconsistent logics to our disposal.

Many of these logics, however, lack the inferential power and the dynamics to model how we actually treat information tainted by inconsistency. An exception in this respect is Batens’ inconsistency-adaptive approach, in which all rules of classical logic are applicable to those parts of our premise set which we can safely consider untainted by inconsistency, without having to specify beforehand which parts of our premises behave consistently.

In order to bring this dynamic approach to paraconsistency closer to our actual argumentative practice, we use its machinery to extend the paraconsistent approach to dialogical logic as developed by Rahman and Carnielli. This way, we obtain a very powerful formalism for the systematic study of dialogues in which two parties exchange arguments over a central claim, in the possible presence of inconsistent information.

* Instituto de Investigaciones Filosóficas (IIF) - Universidad National Autonoma de México (UNAM)

Joint work with Matthieu Fontaine (IIF-UNAM)