Décio Krause

In this paper we discuss some questions proposed by Prof. Newton da Costa on the foundations of quasi-set theory. His main doubts concern the possibility of a reasonable semantical understanding of the theory, mainly due to the fact that identity and difference do not apply to some entities of the theory’s intended domain of discourse. According to him, the quantifiers employed in the theory, when understood in the usual way, rely on the assumption that identity applies to all entities in the domain of discourse. Inspired by his provocation, we suggest that, using some ideas presented by da Costa himself in his seminars at UFSC and by one of us in some papers, these difficulties can be overcome both on a formal level and on an informal level, showing how quantification over items for which identity does not make sense can be understood without presupposing a semantics based on a ‘classical’ set theory.

Quasi-set theory has been proposed as a means of handling collections of indiscernible objects. Although the most direct application of the theory is quantum physics, it can be seen per se as a non-classical logic (a non-reflexive logic). In this paper we revise and correct some aspects of quasi-set theory as presented in [12], so as to avoid some misunderstandings and possible misinterpretations about the results achieved by the theory. Some further ideas with regard to quantum field theory are also advanced in this paper

A investigação de um domínio amplo da realidade, como a evolução dosseres vivos, pode dar origem a diferentes “teorias”, cada uma consoantecom uma particular perspectiva que se considere. Para que se proceda auma análise detalhada dos pressupostos e conceitos que baseiam umadeterminada visão, o método axiomático parece ser a melhor das opções.Neste artigo, são discutidas algumas teorias da biologia evolutiva de umponto de vista axiomático, mostrando-se de que forma se pode apresentarum “predicado de Suppes” para a teoria sintética da evolução, comodetalhado em outro local . Estaformulação é utilizada, dentre outras coisas, para se discutir a noção deaptidão darwiniana, bem como para explorar as relações entre a teoriadarwiniana da seleção natural e a genética de populações.The investigation of a wide field of knowledge, as evolution of living beings,may originate different “theories”, each one acting as a particularperspective we have about the domain. In order to proceed a philosophicalanalysis of the underlying assumptions of a particular view, it seems thatthe use of the axiomatic method is still the better way. Here, we discuss some theories of evolutionary biology from an axiomatic point of view, bymeans of a Suppes predicate for the synthetic theory of evolution, alreadydetailed in MAGALHÃES and KRAUSE . This formulation is hereused, among other things, to deal with the concept of Darwinian fitness, soas to explore the relationships between Darwinian theory and populationgenetics

Sortal predicates have been associated with a counting process, which acts as a criterion of identity for the individuals they correctly apply to. We discuss in what sense certain types of predicates suggested by quantum physics deserve the title of ‘sortal’ as well, although they do not characterize either a process of counting or a criterion of identity for the entities that fall under them. We call such predicates ‘quantum-sortal predicates’ and, instead of a process of counting, to them is associated a ‘criterion of cardinality’. After their general characterization, it is discussed how these predicates can be formally described.

We discuss some logico-mathematical systems which deviate from classical logic and mathematics with respect to the concept of identity. In the first part of the paper we present very general formulations of the principle of identity and show how they can be ‘relativized’ to objects and to properties. Then, as an application, we study the particular cases of physics and logic . In the last part of the paper, we discuss the alphabar logics, that is, those logical systems which violate a formulation of one of the most fundamental versions of the principle of identity; in these logics, there are formulas which are not deducible from themselves

This paper intends to introduce the three issues of Principia which will appear in a sequel honoring Newton da Costa’s 80th birthday. Instead of presenting the papers one by one, as it is common in presentations such as this one, we have left the papers speak by themselves, and instead we have preferred to present to the Brazilian readers, specialty to our students, some aspects of Newton da Costa’s conception of science and of the scientific activity, grounded on the concept of quasi-truth, which he contributed to develop in a rigorous way. Da Costa is known as one of the founding fathers of paraconsistent logic, but his contributions go also to the foundations of physics, theoretical computation, model theory, algebraic logic, lattice theory, applications of non-classical logics to law and technology, etc. But perhaps his main contribution was to provide a basis for the birth of a school of logic in our country, serving as teacher and inspiring new researchers for generations. It is a pleasure to have had so enthusiastic acceptation from the editors of Principia to organize these volumes. I would like to thank the contributors and the editors of Principia, specially Prof. Cezar Mortari for his help in organizing the issue.