John Horty

College Park, Maryland, United States of America
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Ought to Do In Agency and deontic logic, Oxford University Press. 2001.
An analogy is developed between action in an indeterministic setting and choice under uncertainty, as it is studied in decision theory. Various dominance relations among actions are explored, and used both to provide a semantic account of what agents ought to do and to formulate a notion of dominance act utilitarianism. The ideas are related to problems involving independence, conditionals, and sure‐thing reasoning.
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Conditional Oughts In Agency and deontic logic, Oxford University Press. 2001.
The notion of what an agent ought to do is refined to yield a notion conditional obligation, representing what the agent ought to do under various circumstances. Patterns of reasoning in the conditional deontic logic are explored. In contrast to the dominance account developed earlier, a competing notion of orthodox act utilitarianism is formulated.
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Strategic Oughts In Agency and deontic logic, Oxford University Press. 2001.
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 …Read more
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Indeterminism and Agency In Agency and deontic logic, Oxford University Press. 2001.
Develops the formal theory of action, or agency, that forms the background of the book. The account is cast against the background of Prior's theory of branching, or indeterministic, time. Against this background, the chapter develops precise notions of action and ability for both individuals and groups.
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Group Oughts In Agency and deontic logic, Oxford University Press. 2001.
The notion of what an agent ought to do is generalized to yield a notion of what groups of agents ought to do. Relations among the obligations governing groups and subgroups are explored, as well as the connections among different species of individual act utilitarianism, group act utilitarianism, and rule utilitarianism.
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Ought to Be In Agency and deontic logic, Oxford University Press. 2001.
Supplements the background theory of indeterministic time with a standard deontic logic, representing what ought to be the case. Taken together with the formal notion of action introduced in the previous chapter, the framework now allows us to speak about what it ought to be that the agent does, and to explore the possibility that this notion should be identified with the notion of what the agent ought to do. Examples are developed to show that the two notions should not be identified.
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The Logic of Precedent: Constraint, Freedom, and Common Law Reasoning Cambridge University Press. 2024.
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 it…Read more
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Nonmonotonic Logic In Lou Goble (ed.), The Blackwell Guide to Philosophical Logic, Wiley-blackwell. 2001.
The goal of a logic is to define a consequence relation between a set of formulas Γ and, in most cases, an individual formula A. This definition generally takes one of two forms. From a proof theoretic standpoint, A is said to be a consequence of Γ whenever there is a deduction of A from the set Γ, viewed as a set of premises; from a model theoretic standpoint, A is said to be a consequence of Γ whenever A holds in every model that satisfies each formula in Γ.
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Action Types in Stit Semantics with Eric Pacuit Review of Symbolic Logic 10 (4): 617-637. 2017.
Stit semantics grows out of a modal tradition in the logic of action that concentrates on an operator representing the agency of an individual in seeing to it that some state of affairs holds, rather than on the actions the individual performs in doing so. The purpose of this paper is to enrich stit semantics, and especially epistemic stit semantics, by supplementing the overall framework with an explicit treatment of action types. We show how the introduction of these new action types allows us…Read more
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Modifying the reason model Artificial Intelligence and Law 29 (2): 271-285. 2020.
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 …Read more
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Agency and deontic logic Oxford University Press. 2001.
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 unif…Read more
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Reasoning with dimensions and magnitudes Artificial Intelligence and Law 27 (3): 309-345. 2019.
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 …Read more
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Reasons as Defaults Oxford University Press USA. 2012.
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 ar…Read more
• Some Aspects of Meaning in Non-Contingent Language Dissertation, University of Pittsburgh. 1986.
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 …Read more
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Evaluating new options in the context of existing plans with Martha E. Pollack Artificial Intelligence 127 (2): 199-220
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 …Read more
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A sceptical theory of inheritance in nonmonotonic semantic networks with Richmond H. Thomason and David S. Touretzky Artificial Intelligence 42 (2-3): 311-348. 1990.
inheritance reasoning in semantic networks allowing for multiple inheritance with exceptions. The approach leads to a definition of iaheritance that is..
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Frege on definitions: a case study of semantic content Oxford University Press. 2007.
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 ...
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The result model of precedent Legal Theory 10 (1): 19-31. 2004.
The result model of precedent holds that a legal precedent controls a fortiori cases—those cases, that is, that are at least as strong for the winning side of the precedent as the precedent case itself. This paper defends the result model against some objections by Larry Alexander, drawing on ideas from the field of Artificial Intelligence and Law in order to define an appropriate strength ordering for cases
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Rules and reasons in the theory of precedent Legal Theory 17 (1): 1-33. 2011.
The doctrine of precedent, as it has evolved within the common law, has at its heart a form of reasoning—broadly speaking, alogic—according to which the decisions of earlier courts in particular cases somehow generalize to constrain the decisions of later courts facing different cases, while still allowing these later courts a degree of freedom in responding to fresh circumstances. Although the techniques for arguing on the basis of precedent are taught early on in law schools, mastered with rel…Read more
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Moral dilemmas and nonmonotonic logic Journal of Philosophical Logic 23 (1). 1994.
From a philosophical standpoint, the work presented here is based on van Fraassen [26]. The bulk of that paper is organized around a series of arguments against the assumption, built into standard deontic logic, that moral dilemmas are impossible; and van Fraassen only briefly sketches his alternative approach. His paper ends with the conclusion that “the problem of possibly irresolvable moral conflict reveals serious flaws in the philosophical and semantic foundations of ‘orthodox’ deontic logi…Read more
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A Clash of Intuitions: The Current State of Nonmonotonic Multiple Inheritance Systems with Richmond H. Thomason
Early attempts at combining multiple inheritance with nonmonotonic reasoning were based on straightforward extensions of tree-structured inheritance systems, and were theoretically unsound. In The Mathcmat~'cs of Inheritance Systcrns, or TMOIS, Touretzky described two problems these systems cannot handle: reasoning in the presence of true but redundant assertions, and coping with ambiguity. TMOIS provided a definition and analysis of a theoretically sound multiple inheritance system, accom-
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Synthese
The purpose of this paper is to explore a new deontic operator for representing what an agent ought to do; the operator is cast against the background of a modal treatment of action developed by Nuel Belnap and Michael Perlo, which itself relies on Arthur Prior's indeterministic tense logic. The analysis developed here of what an agent ought to do is based on a dominance ordering adapted from the decision theoretic study of choice under uncertainty to the present account of action. It is shown t…Read more
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Reasons as Defaults Oup Usa. 2012.
In this volume, John Horty brings to bear his work in logic to present a framework that allows for answers to key questions about reasons and reasoning, namely: What are reasons, and how do they support actions or conclusions?