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)

Hypercomputation—the hypothesis that Turing-incomputable objects can be computed through infinitary means—is ineffective, as the unsolvability of the halting problem for Turing machines depends just on the absence of a definite value for some paradoxical construction; nature and quantity of computing resources are immaterial. The assumption that the halting problem is solved by oracles of higher Turing degree amounts just to postulation; infinite-time oracles are not actually solving paradoxes, but simply assigning them conventional values. Special values for non-terminating processes are likewise (...) irrelevant, since diagonalization can cover any amount of value assignments. This should not be construed as a restriction of computing power: Turing’s uncomputability is not a ‘barrier’ to be broken, but simply an effect of the expressive power of consistent programming systems. (shrink)

At the heart of my pragmatic theory of truth and ontology is a view of the relation between language and reality which I term internal justification: a way of explaining how sentences may have truth-values which we cannot discover without invoking the need for the mystery of a correspondence relation. The epistemology upon which the theory depend~ is fallibilist and holistic ; places heavy reliance on modal idioms ; and leads to the conclusion that current versions of realism and anti-realism (...) are deficient. Just as my theory avoids the need for an epistemic 'given', it avoids the need for a metaphysical 'given' or 'joints'. I offer a view of the nature of philosophy and what it can properly achieve with respect to ontological questions ; since those views lead me to believe that philosophical discussion about what exists should be restricted to 'entities' discussed in non-philosophical contexts, my views on how we should understand claims made about the existence of middle-sized physical objects, theoretical entities in science, and abstract entities in mathematics, give the thesis a schematic completeness. My theory leads me to a conception of inquiry which defends the cognitive status of moral statements whilst being critical of Kantian and utilitarian approaches to morality. Chapter 1 explores the views of my closest philosophical allies: William James and Nelson Goodman. (shrink)

The liar paradox, attributed to Eubulides, a fifth century BC Greek philosopher, has been debated over two millennia. In the history of philosophy, various attempts have been made to resolve and dissolve the paradox. Nevertheless, the paradox remains as a live area of exploration in logic and philosophy. The present paper is an analytical exploration into the validity of the strengthened liar sentence, which is considered as an acid test for all versions of liar paradoxes. The main method used in (...) this analysis is the Fregean distinction between sign, sense and reference. The Fregean approach towards attributing the truth value as the predicate of the sentence is also used in this analysis. The analysis shows that the liar sentence is essentially meaningless and in a strict sense, it does not qualify as a sentence at all. Considering the liar sentence as meaningful, further analysis of the formal representation of liar sentence again proves it to be necessarily an inconsistent one. The formal analysis brings out the implicit contradiction within the liar sentence. (shrink)

In this paper I discuss Ernst Zermelo’s ideas concerning the possibility of developing a system of infinitary logic that, in his opinion, should be suitable for mathematical inferences. The presentation of Zermelo’s ideas is accompanied with some remarks concerning the development of infinitary logic. I also stress the fact that the second axiomatization of set theory provided by Zermelo in 1930 involved the use of extremal axioms of a very specific sort.1.

Jan Łukasiewicz’s analysis of Aristotle’s syllogism drew attention to the nature of syllogisms as conditionals rather than premise-conclusion arguments. His further idea that syllogisms should be understood as theorems of an axiom system seems a step too far for many logicians. But there is evidence to suggest that Aristotle’s syllogism was to regularise some of the steps made in ‘dialogue games.’ This way of seeing the syllogism is explored in the framework of modern formal dialogue systems. A modern formal syllogistic (...) game, DLSyll, is set out and analysed in use. (shrink)