Décio Krause

We show that using quasi-set theory, or the theory of collections of indistinguishable objects, we can define an algebra that has most of the standard properties of an orthocomplete orthomodular lattice, which is the lattice of all closed subspaces of a Hilbert space. We call the mathematical structure so obtained $\mathfrak{I}$-lattice. After discussing some aspects of such a structure, we indicate the next problem of axiomatizing the corresponding logic, that is, a logic which has $\mathfrak{I}$-lattices as its Lindembaum algebra, which we postpone to a future work. Thus we conclude that the initial intuitions by Birkhoff and von Neumann that the ``logic of quantum mechanics" would be not classical logic, is consonant with the idea of considering indistinguishability right from the start, that is, as a primitive concept. In the first sections, we present the main motivations and a ``classical'' situation which mirrors that one we focus on the last part of the paper. This paper is our first analysis of the algebraic structure of indiscernibility.

The ‘ontic’ form of structural realism , roughly speaking, admits a complete elimination of the objects in the discourse of scientific theories, leaving us with structures only. As put by the defenders of such a claim, the idea is that all there is are structures and, if the relevant structures are to be set-theoretical constructs , as it has also been claimed, then the relations which appear in such structures should be taken to be ‘relations without the relata’. As far as we know, there is not a definition of structure in standard mathematics which fits their intuitions, and even category theory seems not to correspond adequately the OSR claims. Since OSR is also linked with the semantic approach to theories, the structures to be dealt with are taken to be set-theoretical constructs. But these are ‘relational’ structures where the involved relations are built from basic objects , and so no complete elimination of the relata is possible, although it would be adequate for characterizing OSR. In this paper we present a definition of a kind of relation that does not depend on the particular objects being related in the sense that the ‘relation’ continues to hold even if the relata are exchanged by suitable objects. Although there is not a ‘complete’ elimination of relata, our definition might be viewed as an alternative way of finding adequate mathematical ‘set-theoretical’ frameworks for describing at least some of the intuitions regarding OSR within a ‘set-theoretical’ framework

Our aim in this paper is to take quite seriously Heinz Post’s claim that the non-individuality and the indiscernibility of quantum objects should be introduced right at the start, and not made a posteriori by introducing symmetry conditions. Using a different mathematical framework, namely, quasi-set theory, we avoid working within a label-tensor-product-vector-space-formalism, to use Redhead and Teller’s words, and get a more intuitive way of dealing with the formalism of quantum mechanics, although the underlying logic should be modified. We build a vector space with inner product, the Q-space, using the non-classical part of quasi-set theory, to deal with indistinguishable elements. Vectors in Q-space refer only to occupation numbers and permutation operators act as the identity operator on them, reflecting in the formalism the fact of unobservability of permutations. Thus, this paper can be regarded as a tentative to follow and enlarge Heinsenberg’s suggestion that new phenomena require the formation of a new “closed” (that is, axiomatic) theory, coping also with the physical theory’s underlying logic and mathematics

PORTUGUESE: Neste artigo, apresentaremos uma visão particular do desenvolvimento de teorias científicas que denominamos (inspirados em Ortega y Gasset) "perspectivismo". Discutiremos como, através desse enfoque, é possível compatibilizar diversas descrições aparentemente distintas e incompatíveis de uma suposta realidade que se investiga. Fazemos isso distinguindo entre a "realidade" (R) e a "descrição empírica da realidade" (Re). Aceitando que podemos ter diversas descrições empíricas de uma mesma realidade, discutimos o caso particular em que esse esquema é utilizado nos debates atuais acerca da ontologia da física quântica, em especial da mecânica quântica não relativista. Como se sabe, essa teoria é compatível com distintas ontologias (ou metafísicas), em particular, pode ser vista como comprometida com uma ontologia de indivíduos, mas também com uma ontologia de não indivíduos. Ambas as alternativas são plausíveis e merecem ser desenvolvidas. Propomos que o perspectivismo aqui apresentado é neutro com relação à escolha de uma metafísica (ontologia), bem como aos debates entre realistas e antirrealistas em filosofia da ciência. Concluímos que passar do pluralismo aceito pelo perspectivista ao realismo ou antirrealismo envolve comprometimento com teses mais robustas acerca da relação entre realidade e descrição da realidade.ENGLISH: In this article we present a particular view of the development of scientific theories which (following Ortega y Gasset), we term "perspectivism". Making use of this view, we discuss how we can accommodate distinct and apparently incompatible descriptions of a supposed reality under investigation. We distinguish between a "reality" (R) and its "empirical description", (Re). Acknowledging that we can have diverse empirical descriptions of the same reality, we discuss the particular case in which the view is applied to current debates on the ontology of quantum physics, especially of non-relativistic quantum mechanics. As it is well known, this theory is compatible with treating quantum objects either as individuals or as non-individuals. Both ontologies are possible and deserve to be developed. We propose that the perspectivism developed here is neutral not only with respect to the choice of an ontology, but also concerning the debates among realists and anti-realists in the philosophy of science. We conclude that to go beyond the pluralism accepted by perspectivism, and to adopt realism or anti-realism, involves commitment to strong theses about the relation between reality and its descriptions. PORTUGUESE: Neste artigo, apresentaremos uma visão particular do desenvolvimento de teorias científicas que denominamos (inspirados em Ortega y Gasset) "perspectivismo". Discutiremos como, através desse enfoque, é possível compatibilizar diversas descrições aparentemente distintas e incompatíveis de uma suposta realidade que se investiga. Fazemos isso distinguindo entre a "realidade" (R) e a "descrição empírica da realidade" (Re). Aceitando que podemos ter diversas descrições empíricas de uma mesma realidade, discutimos o caso particular em que esse esquema é utilizado nos debates atuais acerca da ontologia da física quântica, em especial da mecânica quântica não relativista. Como se sabe, essa teoria é compatível com distintas ontologias (ou metafísicas), em particular, pode ser vista como comprometida com uma ontologia de indivíduos, mas também com uma ontologia de não indivíduos. Ambas as alternativas são plausíveis e merecem ser desenvolvidas. Propomos que o perspectivismo aqui apresentado é neutro com relação à escolha de uma metafísica (ontologia), bem como aos debates entre realistas e antirrealistas em filosofia da ciência. Concluímos que passar do pluralismo aceito pelo perspectivista ao realismo ou antirrealismo envolve comprometimento com teses mais robustas acerca da relação entre realidade e descrição da realidade.

Schrödinger logics are logical systems in which the principle of identity is not true in general. The intuitive motivation for these logics is both Erwin Schrödinger's thesis that identity lacks sense for elementary particles of modern physics, and the way which physicists deal with this concept; normally, they understand identity as meaning indistinguishability . Observing that these concepts are equivalent in classical logic and mathematics, which underly the usual physical theories, we present a higher-order logical system in which these concepts are systematically separated. A 'classical' semantics for the system is presented and some philosophical related questions are mentioned. One of the main characteristics of our system is that Leibniz' Principle of the Identity of Indiscernibles cannot be derived. This fact is in accordance with some authors who maintain that quantum mechanics violates this principle. Furthermore, our system may be viewed as a way of making sense some of Schrödinger's logical intuitions about the nature of elementary particles

We critically examine the claim that identity is a fundamental concept. According to those putting forward this thesis, there are four related reasons that can be called upon to ground the fundamental character of identity: identity is presupposed in every conceptual system; identity is required to characterize individuality; identity cannot be defined; the intelligibility of quantification requires identity. We address each of these points and argue that none of them advances compelling reasons to hold that identity is fundamental; in fact, most of the tasks that seem to require identity may be performed without identity. So, in the end, identity may not be a fundamental concept after all.

We investigate the higher-order modal logic , which is a variant of the system presented in our previous work. A semantics for that system, founded on the theory of quasi sets, is outlined. We show how such a semantics, motivated by the very intuitive base of Schrödinger logics, provides an alternative way to formalize some intensional concepts and features which have been used in recent discussions on the logical foundations of quantum mechanics; for example, that some terms like 'electron' have no precise reference and that 'identical' particles cannot be named unambiguously. In the last section, we sketch a classical semantics for quasi set theory

Lowe has recently argued that quantum particles offer examples of vague objects. While accepting the premise of the argument that such particles can be regarded as individuals, we point out that there is a lacuna here, to be filled by a detailed analysis of the nature of the entangled states which they enter into. We then elaborate the alternative view, according to which such particles should be regarded as non- individuals' and situate it in the context of recent developments of a logic of non- individuality. Our conclusion is that it is here that one encounters genuine ontic vagueness.

We consider the claim by Dorato and Morganti 591–610) that primitive individuality should be attributed to the entities dealt with by non-relativistic quantum mechanics. There are two central ingredients in the proposal: in the case of non-relativistic quantum mechanics, individuality should be taken as a primitive notion and primitive individuality is naturalistically acceptable. We argue that, strictly understood, naturalism faces difficulties in helping to provide a theory with a unique principle of individuation. We also hold that even when taken in a loose sense, naturalism does not provide any sense in which one could hold that quantum mechanics endorses primitive individuality over non-individuality. Rather, we argue that non-individuality should be preferred based on the grounds that such a view fits better the claims of the theory

In this paper we consider the notions of structure and models within the semantic approach to theories. To highlight the role of the mathematics used to build the structures which will be taken as the models of theories, we review the notion of mathematical structure and of the models of scientific theories. Then, we analyse a case-study and argue that if a certain metaphysical view of quantum objects is adopted, one seeing them as non-individuals, then there would be strong reasons to ask for a different mathematical framework for describing the structures that would be the models of the corresponding theory. In departing from the standard frameworks (those worked on within standard mathematics), we hope to bring to the scene, within the scope of the semantic approach, the importance of paying attention to some fundamental concepts usually only superficially touched by philosophers of science (if touched).

Some of the forerunners of quantum theory regarded the basic entities of such theories as 'non-individuals'. One of the problems is to treat collections of such 'things', for they do not obey the axioms of standard set theories like Zermelo- Fraenkel. In this paper, collections of objects to which the standard concept of identity does not apply are termed 'quasi-sets'. The motivation for such a theory, linked to what we call 'the Manin problem', is presented, so as its specific axioms. At the end, it is shown how quantum statistics can be obtained within quasi-set thbeory.

Is there vagueness in the world? This is the central question that we are concerned with. Focusing on identity statements around which much of the recent debate has centred, we argue that `vague identity' arises in quantum mechanics in one of two ways. First, quantum particles may be described as individuals, with `entangled' states understood in terms of non-supervenient relations. In this case, the vagueness is ontic but exists at the level of these relations which act as a kind of `veil'. Secondly, the particles can be regarded as non-individuals, where this is understood as a lack of self-identity and given formal expression in terms of quasi-set theory. Here we have ontic vagueness at perhaps the most basic metaphysical level. Our conclusion is that there is genuine vagueness `in the world' but how it is understood depends on the metaphysical package adopted.

Paraconsistent logics are logics that can be used to base inconsistent but non-trivial systems. In paraconsistent set theories, we can quan- tify over sets that in standard set theories, if consistent, would lead to contradictions, such as the Russell set, R = fx : x =2 xg. Quasi-set theories are mathematical systems built for dealing with collections of indiscernible elements. The basic motivation for the development of quasi-set theories came from quantum physics, where indiscernible entities need to be considered. Usually, the way of dealing with indiscernible objects within clas- sical logic and mathematics is by restricting them to certain structures, in a way so that the relations and functions of the structure are not sufficient to individuate the objects; in other words, such structures are not rigid. In quantum physics, this idea appears when symmetry conditions are introduced, say by choosing symmetric and anti-symmetric functions in the relevant Hilbert spaces. But in standard mathematics, such as that built in Zermelo-Fraenkel set theory, any structure can be extended to a rigid structure. That means that, although we can deal with certain objects as they were indiscernible, we realize that from out- side of these structures these objects are no more indiscernible, for they can be individualized in the extended rigid structures: ZF is a theory of individuals, distinguishable objects. In quasi-set theory, it seems that there are structures that cannot be extended to rigid ones, so it seems that they provide a natural mathematical framework for expressing quantum facts without certain symmetry suppositions. There may be situations, however, in which we may need to deal with inconsistent bits of infor- mation in a quantum context, even if these informations are concerned with ways of speech. Furthermore, some authors think that superposi- tions may be understood in terms of paraconsistent logics, and even the notion of complementarity was already treated by such a means. This is, apparently, a nice motivation to try to merge these two frameworks. In this work, we develop the technical details, by basing our quasi-set theory in the paraconsistent system C1. We also elaborate a new hierarchy of paraconsistent calculi, the paraconsistent calculi with indiscernibility. For the finalities of this work, some philosophical questions are outlined, but this topic is left to a future work.

This paper is the sequel of a previous one where we have introduced a paraconsistent logic termed paraclassical logic to deal with 'complementary propositions'. Here, we enlarge upon the discussion by considering certain 'meaning principles', which sanction either some restrictions of 'classical' procedures or the utilization of certain 'classical' incompatible schemes in the domain of the physical theories. Here, the term 'classical' refers to classical physics. Some general comments on the logical basis of a scientific theory are also put in between the text, motivated by the discussion of complementarity.