Imperatives cannot be true or false, so they are shunned by logicians. And yet imperatives can be combined by logical connectives: "kiss me and hug me" is the conjunction of "kiss me" with "hug me". This example may suggest that declarative and imperative logic are isomorphic: just as the conjunction of two declaratives is true exactly if both conjuncts are true, the conjunction of two imperatives is satisfied exactly if both conjuncts are satisfied—what more is there to say? Much more, (...) I argue. "If you love me, kiss me", a conditional imperative, mixes a declarative antecedent ("you love me") with an imperative consequent ("kiss me"); it is satisfied if you love and kiss me, violated if you love but don't kiss me, and avoided if you don't love me. So we need a logic of three -valued imperatives which mixes declaratives with imperatives. I develop such a logic. (shrink)

It is not uncommon in the history of science and philosophy to encounter crucial experiments or crucial objections the truth-value of which we are ignorant, that is, about which we suspend judgment. Should we ignore such objections? Contrary to widespread practice, I show that in and only in some circumstances they should not be ignored, for the epistemically rational doxastic attitude is to suspend judgment also about the hypothesis that the objection targets. In other words, suspension of judgment “propagates” from (...) the crucial objection to the hypothesis. In this paper I study under which conditions this phenomenon occurs, and discuss its significance for the topics of skepticism, scientific realism, and peer disagreement. (shrink)

The book provides a historical and systematic exposition of the semantic theory of truth formulated by Alfred Tarski in the 1930s. This theory became famous very soon and inspired logicians and philosophers. It has two different, but interconnected aspects: formal-logical and philosophical. The book deals with both, but it is intended mostly as a philosophical monograph. It explains Tarski’s motivation and presents discussions about his ideas as well as points out various applications of the semantic theory of truth to philosophical (...) problems. (shrink)

Este livro se propõe a ser uma introdução fácil e acessível, porém rigorosa e tecnicamente precisa, à lógica. Prioridade é dada à clareza e lucidez na explicação das definições e teoremas, bem como à aplicação prática da lógica na análise de argumentos. O livro foi concebido de forma a permitir sua utilização por qualquer pessoa interessada em aprender lógica, independentemente de sua área de atuação ou bagagem teórica prévia. Em especial, ele deve ser útil a estudantes e professores de filosofia, (...) computação e matemática. (shrink)

I propose a comprehensive account of negation as a modal operator, vindicating a moderate logical pluralism. Negation is taken as a quantifier on worlds, restricted by an accessibility relation encoding the basic concept of compatibility. This latter captures the core meaning of the operator. While some candidate negations are then ruled out as violating plausible constraints on compatibility, different specifications of the notion of world support different logical conducts for negations. The approach unifies in a philosophically motivated picture the following (...) results: nothing can be called a negation properly if it does not satisfy Contraposition and Double Negation Introduction; the pair consisting of two split or Galois negations encodes a distinction without a difference; some paraconsistent negations also fail to count as real negations, but others may; intuitionistic negation qualifies as real negation, and classical Boolean negation does as well, to the extent that constructivist and paraconsistent doubts on it do not turn on the basic concept of compatibility but rather on the interpretation of worlds. (shrink)

This article argues that existing systems on the Web cannot approach human-level intelligence, as envisioned by Descartes, without being able to achieve genuine problem solving on unseen problems. The article argues that this entails committing to a strong intensional logic. In addition to revising extant arguments in favor of intensional systems, it presents a novel mathematical argument to show why extensional systems can never hope to capture the inherent complexity of natural language. The argument makes its case by focusing on (...) representing, with increasing degrees of complexity, knowledge in a first-order language. Nevertheless, the attempts at representation fail to achieve consistency, making the case for an intensional representation system for natural language clear. (shrink)

In this paper, after clarifying certain features of Gideon Rosen’s Modal Fictionalism, I raise two problems for that view and argue that these problems strongly suggest that advocates of a “Deflationist Strategy” ought not to endorse, or adopt Rosen-style Modal Fictionalism.

After a number of general considerations, without meaning in any sense a reductionist approach, this paper argues in favour of the mathematics of discrete systems and of the non-classical logics, and claims that a complex thinking both entails and crosses through those domains. Such a proposal, it is argued, has not been a general concern until to-date among the communities of complexologists. At the end, several consequences are withdrawn at understanding what truly thinking about complexity is all about. Luego de (...) varias consideraciones de orden general, y sin que se asuma en absoluto una postura reduccionista, este texto argumenta a favor de la tesis según la cual pensar la complejidad con la ciencia de punta implica considerar los modos y grados como las matemáticas de sistemas discretos y las lógicas no-clásicas contribuyen a la dilucidación de lo que es un pensar la complejidad. Estas consideraciones no han sido incorporadas en general por parte de la comunidad de complejólogos. Al final se extraen algunas de las consecuencias de lo que, consiguientemente, sea pensar la complejidad. (shrink)

In this paper, I provide a novel approach to the issue of religious diversity: I reject classical pluralist approaches to the issue, such as John Hick’s, and argue that their attempts to construe commonalities between the religions are contrived. The reason that they attempt to find commonalities at all costs is that they presuppose a bivalent notion of truth according to which that which is different is false. I suggest that, in order to get a robust theory on religious diversity (...) off the ground, we should rely on the notion of justification rather than that of bivalent truth. Justification is pluralizable, dependent upon the circumstances, whereas bivalent truth is not. Armed with a pluralizable notion of justification, we can acknowledge that other religious beliefs are genuinely different without necessarily being false: They can be justified, given the circumstances a believer of a different religion is in. Perceiving religious differences in this way allows to liberate the interreligious dialogue from the pressure to find commonalities between religions at all costs, to respect the religious Other in her Otherness, and to ‘mirror’ one’s own religion in light of other religions. (shrink)

The rich body of physical theories defines the foundation of our understanding of the world. Its mathematical formulation is based on classical Aristotelian logic. In the philosophy of science the ambiguities, paradoxes, and the possibility of subjective interpretations of facts have challenged binary logic, leading, among other developments, to Gotthard Günther’s theory of polycontexturality. Günther’s theory explains how observers with subjective perception can become aware of their own subjectivity and provides means to describe contradicting or even paradox observations in a (...) logically sound formalism. Here we summarize the formalism behind Günther’s theory and apply it to two well-known examples from physics where different observers operate in distinct and only locally valid logical systems. Using polycontextural logic we show how the emerging awareness of these limitations of logical systems entails the design of mathematical transformations, which then become an integral part of the theory. In our view, this approach offers a novel perspective on the structure of physical theories and, at the same time, emphasizes the relevance of the theory of polycontexturality in modern sciences. (shrink)