In this thesis I will test Yagisawa´s Extended Modal Theory of modality against two issues: the problem of accidental intrinsic properties and the problem of transworld identification. Both are part of the recurring criticism of theories supporting transworld individuals, such as the Extended Modal Theory. The first is based on Lewis criticism that argues that if a theory claims that individuals exist in more than one possible world, then transworld individuals do not possess intrinsic properties, only external ones. The second follows the rational of Quine, that argues that because anything can become anything by follow a chain of possible worlds, it becomes problematic in some cases to “discover” the modal stage of a transworld individual in another possible world. The discussion concludes that despite of the criticism above, Yagisawa provides convincing arguments to support transworld identity and EMR does a better job than the Counterpart theory in explaning modality.

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Made available in DSpace on 2014-07-29T15:06:24Z (GMT). No. of bitstreams: 1 RENATO MENDES ROCHA.pdf: 735741 bytes, checksum: 6559707c78ce13d85086e58b691dd7f3 (MD5) Previous issue date: 2010-08-30 / In this dissertation we will defend Lewis Modal Realism (LMR), i.e., the metaphysical hypothesis about the real existence of a plurality of worlds. We will try to show the pragmatic character of Lewis arguments in support of this metaphysics of possible worlds. In this sense, we approximate Lewis (1986) and Quine (1960) and we aim to show that Lewis uses criteria for taking ontological decisions similar to those defended by Quine. These criteria are: simplicity of formulation, theoretical economy and distrust in purely intuitive criteria as only guide for Philosophy. To accomplish our intention, we divided the text in three chapters. In the first we present the philosophical benefits of LMR that demonstrate the theoretical utility of possible-worlds talk. These benefits are related to important concepts in Philosophy of Language and Epistemology, such as, Modality, Counterfactuals and a uniform treatment to Properties and Propositions. The second chapter is divided into two parts. At first we present the philosophical background we believe is related to Lewis philosophy. A neo-humean scenario and the resumption of metaphysics discussion in contemporary analytic philosophy compose this background. In the second part we present three fundamental thesis formulate by Lewis the consistence of his Modal Realism: concreteness, isolation and plenitude. In the third and latter chapter we discuss two criticism of LMR: (a) David Armstrong & Peter Forrest (1984) and (b) Susan Haack (1977). Each of these papers present criticism from distinct points of view. The first aims to identify a paradox in the metaphysics of possible worlds, and the latter focuses on semantics aspects of LMR. Finally, we show Lewis reply to objection (a) and that argument (b) could be inserted as an incredulous stare on LMR, and that it consists on a petition principi. / Nessa dissertação defenderemos o Realismo Modal de David Lewis (RML), ou seja, a hipótese metafísica acerca da existência real de uma pluralidade de mundos. A defesa que apresentaremos procura evidenciar o caráter pragmático dos argumentos a favor dessa metafísica dos mundos possíveis. Nesse sentido, aproximaremos a filosofia de David Lewis (1986) a de W. V. O. Quine (1960) e procuraremos mostrar que Lewis utiliza critérios para tomada de decisões ontológicas semelhantes aos defendidos por Quine. Esses critérios são: a simplicidade de formulação, a economia teórica e a desconfiança de critérios meramente intuitivos como guias para a Filosofia. Para cumprir nosso objetivo, estruturamos a dissertação em três capítulos. No primeiro apresentamos benefícios filosóficos do RML que demonstram a utilidade teórica do idioma dos mundos possíveis. Esses benefícios estão relacionados a noções importantes para a Filosofia da Linguagem e a Teoria do Conhecimento tais como: Modalidades, Contrafatuais, e um tratamento uniforme para Propriedades e Proposições. O segundo capítulo divide-se em duas partes. Na primeira traçamos um pano de fundo filosófico que acreditamos estar relacionado à filosofia de Lewis. Compõem esse pano de fundo: um cenário que identificamos como neo-humeano e a retomada de discussões metafísicas na Filosofia Analítica Contemporânea. Na segunda parte apresentamos três teses formuladas por Lewis para garantir a consistência e a coerência de seu Realismo Modal: a Concretude, o Isolamento e a Plenitude. No terceiro capítulo discutimos duas críticas ao RML: (a) David Armstrong & Peter Forrest (1984) e (b) Susan Haack (1977). Cada um desses artigos apresenta uma crítica diferente. A primeira procura identificar um paradoxo na metafísica dos mundos possíveis e a segunda concentra-se em aspectos semânticos do RML. Por fim, mostramos como a objeção em (a) é refutada por Lewis e como o argumento em (b) poderia se inserir no grupo de críticas que Lewis classifica como um olhar incrédulo sobre o RML. Por isso, concluímos que esse olhar consiste em uma petição de princípio.

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Lewisian Genuine Realism (GR) about possible worlds is often deemed unable to accommodate impossible worlds and reap the benefits that these bestow to rival theories. This thesis explores two alternative extensions of GR into the terrain of impossible worlds. It is divided in six chapters. Chapter I outlines Lewis’ theory, the motivations for impossible worlds, and the central problem that such worlds present for GR: How can GR even understand the notion of an impossible world, given Lewis’ reductive theoretical framework? Since the desideratum is to incorporate impossible worlds into GR without compromising Lewis’ reductive analysis of modality, Chapter II defends that analysis against (old and new) objections. The rest of the thesis is devoted to incorporating impossible worlds into GR. Chapter III explores GR-friendly impossible worlds in the form of set-theoretic constructions out of genuine possibilia. Then, Chapters IV-VI venture into concrete impossible worlds. Chapter IV addresses Lewis’ objection against such worlds, to the effect that contradictions true at impossible worlds amount to true contradictions tout court. I argue that even if so, the relevant contradictions are only ever about the non-actual, and that Lewis’ argument relies on a premise that cannot be nonquestion- beggingly upheld in the face of genuine impossible worlds in any case. Chapter V proposes that Lewis’ reductive analysis can be preserved, even in the face of genuine impossibilia, if we differentiate the impossible from the possible by means of accessibility relations, understood non-modally in terms of similarity. Finally, Chapter VI counters objections to the effect that there are certain impossibilities, formulated in Lewis’ theoretical language, which genuine impossibilia should, but cannot, represent. I conclude that Genuine Realism is still very much in the running when the discussion turns to impossible worlds.