John Horty

The notion of what an agent ought to do at a moment is generalized to yield a notion of what the agent ought to do over extended periods of time. This requires us to develop the notion of a strategy as a function from moments to actions available at those moments and appropriate notions of strategic dominance. A strategic ought operator is introduced and used to analyze the debate between actualists and possibilists concerning the ways in which an agent's obligations depend on his or her future actions.

Unlike statutory law, which relies on the explicit formulation of rules, common law is thought to emerge from a complex doctrine of precedential constraint, according to which decisions in earlier cases constrain later courts while still allowing these courts the freedom to address new situations in creative ways. Although this doctrine is applied by legal practitioners on a daily basis, it has proved to be considerably more difficult to develop an adequate theoretical account of the doctrine itself. Drawing on recent work in legal theory, as well as AI and law, this book develops a new account of precedential constraint and the balance achieved in the common law between constraint and freedom. This account, which involves construction of a group priority ordering among reasons, is then applied to other topics including the semantics of open-textured predicates and the practice of making exceptions to general rules.

In previous work, I showed how the “reason model” of precedential constraint could naturally be generalized from the standard setting in which it was first developed to a richer setting in which dimensional information is represented as well. Surprisingly, it then turned out that, in this new dimensional setting, the reason model of constraint collapsed into the “result model,” which supports only a fortiori reasoning. The purpose of this note is to suggest a modification of the reason model of constraint that distinguishes it from the result model even in the dimensional setting.

John Horty effectively develops deontic logic (the logic of ethical concepts like obligation and permission) against the background of a formal theory of agency. He incorporates certain elements of decision theory to set out a new deontic account of what agents ought to do under various conditions over extended periods of time. Offering a conceptual rather than technical emphasis, Horty's framework allows a number of recent issues from moral theory to be set out clearly and discussed from a uniform point of view.

This paper shows how two models of precedential constraint can be broadened to include legal information represented through dimensions. I begin by describing a standard representation of legal cases based on boolean factors alone, and then reviewing two models of constraint developed within this standard setting. The first is the “result model”, supporting only a fortiori reasoning. The second is the “reason model”, supporting a richer notion of constraint, since it allows the reasons behind a court’s decisions to be taken into account. I then show how the initial representation can be modified to incorporate dimensional information and how the result and reason models can be adapted to this new dimensional setting. As it turns out, these two models of constraint, which are distinct in the standard setting, coincide once they are transposed to the new dimensional setting, yielding exactly the same patterns of constraint. I therefore explore two ways of refining the reason model of constraint so that, even in the dimensional setting, it can still be separated from the result model.

Although the study of reasons plays an important role in both epistemology and moral philosophy, little attention has been devoted to the question of how, exactly, reasons interact to support the actions or conclusions they do. In this book, John F. Horty attempts to answer this question by providing a precise, concrete account of reasons and their interaction, based on the logic of default reasoning. The book begins with an intuitive, accessible introduction to default logic itself, and then argues that this logic can be adapted to serve as a foundation for a concrete theory of reasons. Horty then shows that the resulting theory helps to explain how the interplay among reasons can determine what we ought to do by developing two different deontic logics, capturing two different intuitions about moral conflicts.In the central part of the book, Horty elaborates the basic theory to account for reasoning about the strength of our own reasons, and also about the related concepts of undercutting defeaters and exclusionary reasons. The theory is illustrated with an application to particularist arguments concerning the role of principles in moral theory. The book concludes by introducing a pair of issues new to the philosophical literature: the problem of determining the epistemic status of conclusions supported by separate but conflicting reasons, and the problem of drawing conclusions from sets of reasons that can vary arbitrarily in strength, or importance.

Frege's writings on meaning are often interpreted within the framework of possible worlds semantics. The resulting theories rely on contingency to account for a variety of linguistic phenomena, such as the behavior of expressions in propositional attitude contexts, or the idea that a definition might fix the reference of an expression without establishing its meaning. In this thesis, I interpret Frege's ideas within a different framework, to provide a semantic theory that is able to account for some of these same phenomena as they occur in a certain non-contingent language , where the possible worlds approach breaks down. ;The first part of the thesis is a detailed study of Frege's writings on sense identity, as well as some of the more modern literature on synonymy. I argue that instead of searching for a single relation of meaning equivalence among expressions, we should expect to find several different relations of meaning congruence. I claim that Frege was committed to this more flexible approach as well. To support my claim, I show that his standards for sense identity were strongly psychological; and then, relying on certain parallels between traditional ideas of definition and concept formation, I describe a problem about the senses of expressions introduced into a language through stipulative definitions. In the second part of the thesis, I develop a simple model of senses as procedures. I then use this model to deal with the problem about the senses of defined expressions set out earlier, and to deal also with the clash between Frege's compositional idea that the sense of a complete expression is assembled from the senses of its parts, and his decompositional idea that we can understand certain incomplete expressions only by first understanding complete expressions in which they occur

This paper contributes to the foundations of a theory of rational choice for artificial agents in dynamic environments. Our work is developed within a theoretical framework, originally due to Bratman, that models resource-bounded agents as operating against the background of some current set of intentions, which helps to frame their subsequent reasoning. In contrast to the standard theory of rational choice, where options are evaluated in isolation, we therefore provide an analysis of situations in which the options presented to an agent are evaluated against a background context provided by the agent’s current plans—commitments to future activities, which may themselves be only partially specified. The interactions between the new options and the background context can complicate the task of evaluating the option, rendering it either more or less desirable in context than it would have been in isolation.  2001 Elsevier Science B.V. All rights reserved.

This paper works within a particular framework for reasoning about actions—sometimes known as the framework of “stit semantics”—originally due to Belnap and Perloff, based ultimately on the theory of indeterminism set out in Prior’s indeterministic tense logic, and developed in full detail by Belnap, Perloff, and Xu [3]. The issues I want to consider arise when certain normative, or decision theoretic, notions are introduced into this framework: here I will focus on the notion of a right action, and so on the formulation of act utilitarianism within this indeterministic setting. The problem is simply that there are two different, and conflicting, ways of defining this notion, both well-motivated, and both carrying intuitive weight.

This paper contributes to our formal understanding of the common law — especially the nature of the reasoning involved, but also its point, or justification, in terms of social coordination. I present two apparently distinct models of constraint by precedent in the common law, establish their equivalence, and argue for a perspective according to which courts are best thought of, not as creating and modifying rules, but as generating a social priority ordering on reasons through a procedure that is piecemeal, distributed, and responsive to particular circumstances

In this short monograph, John Horty explores the difficulties presented for Gottlob Frege's semantic theory, as well as its modern descendents, by the treatment of defined expressions. The book begins by focusing on the psychological constraints governing Frege's notion of sense, or meaning, and argues that, given these constraints, even the treatment of simple stipulative definitions led Frege to important difficulties. Horty is able to suggest ways out of these difficulties that are both philosophically and logically plausible and Fregean in spirit. This discussion is then connected to a number of more familiar topics, such as indexicality and the discussion of concepts in recent theories of mind and language. In the latter part of the book, after introducing a simple semantic model of senses as procedures, Horty considers the problems that definitions present for Frege's idea that the sense of an expression should mirror its grammatical structure. The requirement can be satisfied, he argues, only if defined expressions--and incomplete expressions as well--are assigned senses of their own, rather than treated contextually. He then explores one way in which these senses might be reified within the procedural model, drawing on ideas from work in the semantics of computer programming languages. With its combination of technical semantics and history of philosophy, Horty's book tackles some of the hardest questions in the philosophy of language. It should interest philosophers, logicians, and linguists.

In this chapter, we begin by sketching in the broadest possible strokes the ideas behind two formal systems that have been introduced with to goal of explicating the ways in which reasons interact to support the actions and conclusions they do. The first of these is the theory of defeasible reasoning developed in the seminal work of Pollock; the second is a more recent theory due to Horty, which adapts and develops the default logic introduced by Reiter to provide an account of reasons. However, the implementations are complex enough, in both cases, to prevent anything more than this sketch. And we would not want to give the impression that we think that work on the logic of reasons must follow the path mapped out in either of these theories—indeed, we feel that the field is wide open. In the remainder of the chapter, therefore, will concentrate on a number of issues bearing on the logic of reasons that are either not treated in the work of Pollock and Horty, or whose treatment there is, we feel, either inadequate or incomplete. These are: first, the question of whether it is necessary to understand logical interactions among reasons themselves, rather than simply between reasons and the actions or conclusions they support, and if so, what principles might govern these interactions; second, priority relations among reasons and the notion of reason accrual; and third, some problems posed by undercutting defeat.