In this paper non-normal worlds semantics is presented as a basic, general, and unifying approach to epistemic logic. The semantical framework of non-normal worlds is compared to the model theories of several logics for knowledge and belief that were recently developed in Artificial Intelligence (AI). It is shown that every model for implicit and explicit belief (Levesque), for awareness, general awareness, and local reasoning (Fagin and Halpern), and for awareness and principles (van der Hoek and Meyer) induces a non-normal worlds (...) model validating precisely the same formulas (of the language in question). (shrink)

A suggestion is made for representing iterated deontic modalities in stit theory, the “seeing-to-it-that” theory of agency. The formalization is such that normative sentences are represented as agentive sentences and therefore have history dependent truth conditions. In contrast to investigations in alethic modal logic, in the construction of systems of deontic logic little attention has been paid to the iteration... of the deontic modalities.

Based on a notion of "companions to stit formulas" applied in other papers dealing with astit logics, we introduce "choice formulas" and "nested choice formulas" to prove the completeness theorems for dstit logics in a language with the dstit operator as the only non-truth-functional operator. The main logic discussed in this paper is the basic logic of dstit with multiple agents, other logics discussed include the basic logic of dstit with a single agent and some logics of dstit with multiple (...) agents each of which corresponds to a semantic condition concerning the number of possible choices for agents. (shrink)

It is widely held that we can obtain beliefs and withhold believing propositions directly by performing an act of will. This thesis is sometimes identified with the view that believing is a basic act, an act which is under our direct control. Descartes holds that the will is limitless in relation to belief acquisition and that we must be directly responsible for our beliefs, especially our false beliefs, for otherwise we could draw the blasphemous conclusion that God is responsible for (...) them. For Descartes and his followers judgment and assent are acts of the will which may be made both when they ought and when they ought not to be made. They are expressions of freedom of the will and as such we are directly responsible for the beliefs we acquire. Other philosophers who seem to espouse volitionalism include Aquinas, Locke, Kierkegaard, Newman, James, Pieper, Chisholm and Meiland. (shrink)

One way to obtain a comprehensive semantics for various systems of modal logic is to use a general notion of non-normal world. In the present article, a general notion of modal system is considered together with a semantic framework provided by such a general notion of non-normal world. Methodologically, the main purpose of this paper is to provide a logical framework for the study of various modalities, notably prepositional attitudes. Some specific systems are studied together with semantics using non-normal worlds (...) of different kinds. (shrink)

Throughout the history of philosophy there has been a sustained interest in the concepts of knowledge, truth and meaning; interest in the concepts of error, falsity and nonsense, on the other hand, has been intermittent and spasmodic. Error, for example, has suffered at the expense of knowledge to such an extent that sometimes its very existence has been denied, or it has been explained away as being merely the absence of or privation of knowledge; many theories of truth are so (...) constructed that no place can be found for falsity, and theories about what constitutes making sense pay, on the whole, little heed to what constitutes nonsense. In this paper I hope to do something to redress the balance so far as error is concerned. My remarks are prompted by the hope that, just as we may best understand health through the study of disease, so a consideration of error or failure may throw light on knowledge or success. It is clearly not very informative to say of error, falsity and nonsense that they are merely the absence of knowledge, truth and sense; indeed it is just as laconic as a proposed medical definition of disease as the absence of health. (shrink)