The needs of a real-time reasoner situated in an environment may make it appropriate to view error-correction and non-monotonicity as much the same thing. This has led us to formulate situated (or step) logic, an approach to reasoning in which the formalism has a kind of real-time self-reference that affects the course of deduction itself. Here we seek to motivate this as a useful vehicle for exploring certain issues in commonsensereasoning. In particular, a chief drawback of more traditional logics is avoided: from a contradiction we do not have all wffs swamping the (growing) conclusion set. Rather, we seek potentially inconsistent, but nevertheless useful, logics where the real-time self-referential feature allows a direct contradiction to be spotted and corrective action taken, as part of the same system of reasoning. Some specific inference mechanisms for real-time default reasoning are suggested, notably a form of introspection relevant to default reasoning. Special treatment of ...

The kind of resource limitation that is most evident in commonsense reasoners is the passage of time while the reasoner reasons. There is not necessarily any fixed and final set of consequences with which such a reasoning agent ends up. In formalizing commonsense reasoners, then, one must be able to take into account that time is passing as the reasoner is reasoning. The reasoner can then make use of such information in subsequent deductions. Step-logic is such a formalism. It was developed in [Elgot-Drapkin, 1988] to model the ongoing process of deduction. Conclusions are drawn step-by-step. There is no "final" state of reasoning; the emphasis is on intermediate conclusions. In this paper we use step-logic to model the Three-wise-men Problem. Although others have formalized this problem, they have ignored the time aspect that is inherent in the problem: a correct assessment of the situation is made by recognizing that the reasoning process takes time and determining that the other wis...

The true belief components of Plato's tripartite definition of knowledge as justified true belief are represented in formal epistemology by modal logic and its possible worlds semantics. At the same time, the justification component of Plato's definition did not have a formal representation. This

: In this survey, I attempt to identify and describe some of the common threads that tie together work in reasoning about knowledge in such diverse fields as philosophy, economics, linguistics, artificial intelligence, and theoretical computer science, with particular emphasis on work of the past five years, particularly in computer science. This articule is essentially the same as one that appears in Handbook of of Logic in Artificial Intelligence and Logic Programming, Vol. 4, D. Gabbay, C. J. Hogger, and J. A. Robinson, eds., Oxford University Press, 1995, pp. 1--34. It is a revised and updated version of a paper entitled "Reasoning about knowledge: a survey circa 1991", which appears in the Encyclopedia of Computer Science and Technology, Vol. 27, Supplement 12 (ed. A. Kent and J. G. Williams), Marcel Dekker, 1993, pp. 275--296. That article, in turn is a revision of an article entitled "Reasoning About Knowledge: An Overview" that appears in Theoretical Aspects of Reasoning Abou...

1. What are called ‘intuitions ’ in philosophy are just applications of our ordinary capacities for judgement. We think of them as intuitions when a special kind of scepticism about those capacities is salient. 2. Like scepticism about perception, scepticism about judgement pressures us into conceiving our evidence as facts about our internal psychological states: here, facts about our conscious inclinations to make judgements about some topic rather than facts about the topic itself. But the pressure should be resisted, for it rests on bad epistemology: specifically, on an impossible ideal of unproblematically identifiable evidence. 3. Our resistance to scepticism about judgement is not simply epistemic conservativism, for we resist it on behalf of others as well as ourselves. A reason is needed for thinking that beliefs tend to be true. 4. Evolutionary explanations of the tendency assume what they should explain. Explanations that appeal to constraints on the determination of reference are more promising. Davidson’s truth-maximizing principle of charity is examined but rejected. 5. An alternative principle is defended on which the nature of reference is to maximize knowledge rather than truth. It is related to an externalist conception of mind on which knowing is the central mental state. 6. The knowledge-maximizing

This paper is devoted to the study of self-referential proofs and/or justifications, i.e., valid proofs that prove statements about these same proofs. The goal is to investigate whether such self-referential justifications are present in the reasoning described by standard modal epistemic logics such as S4. We argue that the modal language by itself is too coarse to capture this concept of self-referentiality and that the language of justification logic can serve as an adequate refinement. We consider well-known modal logics of knowledge/belief and show, using explicit justifications, that S4, D4, K4, and T with their respective justification counterparts LP, JD4, J4, and JT describe knowledge that is self-referential in some strong sense. We also demonstrate that self-referentiality can be avoided for K and D. In order to prove the former result, we develop a machinery of minimal evidence functions used to effectively build models for justification logics. We observe that the calculus used to construct the minimal functions axiomatizes the reflected fragments of justification logics. We also discuss difficulties that result from an introduction of negative introspection.

this paper---at step i

. There has been a growing interest in AI in formal, qualitative models of various mental attitudes, starting with the well-researched concepts of knowledge and belief, and continuing with more exotic notions such as goals and intentions. In this initial survey we take stock of the work carried out so far in this field, including the motivation for this line of research, the mental attitudes considered, those not, the (primarily logical) tools used, and some of the outstanding problems. 1 Introduction In this paper we review work on formal, qualitative, explicit models of mental attitudes, as studied in recent years in AI. By `mental attitudes' we mean notions such as knowledge, belief, desires, goals, and so on -- those notions, usually attributed to humans, which are generally associated with people's mental life. We use the term `mental state' to denote the collection of all mental attitudes of an agent. Why does AI care about theories of mental state? To start with, to the extent ...

According to the pragmatic or functional conception of attitudes, we can say that John desires A iff John behaves such that he tends to bring it about that the actual world is an A-world, if his beliefs are true. This puts certain constraints on how to analyse desire attributions, but it leaves open a number of alternative analyses. Several alternatives will be discussed and compared in this paper. It will be suggested that for the semantic analysis of desire attributions it is useful to look at recent analyses of belief revision and theories of action and rational choice.

This paper presents a solution in a first-order monotonic logic to a simplified version of the Surprise Birthday Present Problem, a challenge problem for the formal commonsense reasoning community. The problem concerns two siblings who wish to surprise their sister with a present for her birthday: the aim is to construct a theory that will support the desired inferences, not allow undesired inferences, and be sufficiently elaboration tolerant to support reasoning about problem variations. The theory presented in this paper includes the development of a possible-worlds analysis of the concept of surprise, and an extension to previous work on multiple-agent planning to handle joint planning and actions. We show that this theory can solve the original SBP as well as many of its variants.