It's natural to think that the principles expressed by the statements "Promises ought to be kept" and "We ought to help those in need" are defeasible. But how are we to make sense of this defeasibility? On one proposal, moral principles have hedges or built-in unless clauses specifying the conditions under which the principle doesn't apply. On another, such principles are contributory and, thus, do not specify which actions ought to be carried out, but only what counts in favor or (...) against them. Drawing on a defeasible logic framework, this paper sets up three models: one model for each proposal, as well as a third model capturing a mixed view on principles that combines them. It then explores the structural connections between the three models and establishes some equivalence results, suggesting that the seemingly different views captured by the models are closer than standardly thought. (shrink)

Um dos principais resultados da analítica existencial de Ser e Tempo é a prioridade dopossível sobre o efetivo no modo de ser da existência humana. A possibilidade tem um significadofundacional na estruturação modal da existência. Neste artigo, apresento o esboçode uma noção existencial de necessidade. Seguindo um caminho aberto por Oskar Becker,identifico o existencialmente necessário nos limites da projeção em possibilidades existenciais,isto é, na historicidade autêntica do Dasein. Concentrando-me na noção de destino,apresento um conceito de necessidade existencial baseado na simplicidade (...) e na obrigaçãode uma existência condicionada por finitude e liberdade finita. (shrink)

A Leibnizian semantics proposed by Becker in 1952 for the modal operators has recently been reviewed in Copeland’s paper The Genesis of Possible World Semantics (Copeland in J Philos Logic 31:99–137, 2002 ), with a remark that “neither the binary relation nor the idea of proving completeness was present in Becker’s work”. In light of Frege’s celebrated Sense-Determines-Reference principle, we find, however, that it is Becker’s semantics, rather than Kripke’s semantics, that has captured the true spirit of Frege’s semantic program. (...) Furthermore, for Kripke’s possible world semantics to fit in Frege’s framework of senses , worlds and referents , it will have to be thoroughly reformulated. By introducing the notion of a hi-world into the picture, we manage to keep the key ingredients of Becker’s semantics intact, while at the same time solve a fatal problem that used to shadow Becker’s original semantics—it had not been able to make sense of inhomogeneous modality. The resulting generalized Beckerian semantics provides, in effect, a Beckerian analysis of the Kripkean possible worlds. It reveals the subtle hierarchical internal structure of a Kripkean world that has not been discovered before. (shrink)

Both Lowe and Tsai have presented their own versions of the theory that both indicative and subjunctive conditionals are strict conditionals. We critically discuss both versions and we find each version wanting.

It is generally believed that, for a one-off Prisoner’s Dilemma game, it is logical to defect. However, both players cooperating is apparently a better choice than both defecting, hence the dilemma. In this paper, by resorting to Ramsey’s Test, Kripke’s possible world semantics, and Stalnaker/Lewis-style account of conditionals, I show that the first horn of the Prisoner’s Dilemma is an unsound argument. It originates from failing to differentiate between a possible world and a possible set of possible worlds and failing (...) to observe that the set of accessible possible worlds associated with a possible world in general varies from conditional to conditional. This phenomenon can also be illustrated in terms of the recently developed hi-world semantics. Moreover, a meta-argument is constructed to establish the non-existence of a logical argument for defection. (shrink)

This article traces the development of possible worlds semantics through the work of: Wittgenstein, 1913-1921; Feys, 1924; McKinsey, 1945; Carnap, 1945-1947; McKinsey, Tarski and Jónsson, 1947-1952; von Wright, 1951; Becker, 1952; Prior, 1953-1954; Montague, 1955; Meredith and Prior, 1956; Geach, 1960; Smiley, 1955-1957; Kanger, 1957; Hintikka, 1957; Guillaume, 1958; Binkley, 1958; Bayart, 1958-1959; Drake, 1959-1961; Kripke, 1958-1965.

Abstract.The starting point of deontic logic is the distinction between non‐normative necessity and normative necessity. The first part of the paper shows that the distinction between normative necessity and non‐normative necessity occurs already in Aristotle's Orgunon. The second part of the paper makes a further distinction within normative deon itself: The distinction between deontic deon and anankastic deon. Anankastic deon behaves differently from deontic deon in a very important respect: Deontic indifference has no anankastic counterpart.

Abstract.The paper offers a critical survey of two main sorts of problems hindering the possibility of conceiving deontic logic as a suitable account of the logical behaviour of (sentences expressing) legal norms. The notion of “legal norm” is viewed as the main source of the first sort of problems: (a) the typological variety of legal norms requires an account both of the differing logical behaviour of (sentences expressing) differing legal norms, and of the relations which might hold amon them; (b) (...) the ontologic, semantic, and epistemic features of legal norms shed doubt on the very attempt to figure out a logical analysis of (sentences expressing) legal norms. The notion of “systemic legal validity” is viewed as the main source of the second sort of problems: Deontic logic does not provide suitable logical tools to account for legal phenomena like enactment, derogation, and conflicts between legal norms which rely on systemic legal validity. (shrink)