• Handbook of Deontic Logic and Normative System, Volume 2 (edited book)
    with Dov Gabbay, ,, Xavier Parent, Ron van der Meyden, and Leon van der Torre
    College Publications. forthcoming.
  • Skepticism and floating conclusions
    Artificial Intelligence 135 (1-2): 55-72. 2002.
  •  9
    Modifying the reason model
    Artificial Intelligence and Law 29 (2): 271-285. 2021.
    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
  • The Handbook of Deontic Logic (Vol. II) (edited book)
    with Dov Gabbay, Ron van der Meyden, Xavier Parent, and Leandert van der Torre
    College Publications. forthcoming.
  •  65
    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
  •  22
    Epistemic Oughts in Stit Semantics
    Ergo: An Open Access Journal of Philosophy 6. 2019.
  •  34
    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
  •  28
    Action types in stit semantics
    Review of Symbolic Logic 10 (4): 617-637. 2017.
  • 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
  •  62
    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
  •  42
    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..
  •  60
    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 ...
  •  72
    Defaults with Priorities
    Journal of Philosophical Logic 36 (4): 367-413. 2007.
  •  97
    Agency and obligation
    Synthese 108 (2). 1996.
    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 Perloff, 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…Read more
  •  24
    This book provides a unified account of Hansson’s work on values (or preferences), norms, and their interrelations. Although much of the detailed material contained here appears among the numerous articles published by the author over the past decade or so, the book presents this work as a coherent whole. The overall style is formal: definitions are set out, results are established. Readers who do not enjoy formal work in value theory are likely to find little of interest here. But readers who d…Read more
  •  41
    Requirements, Oughts, Intentions
    Philosophy and Phenomenological Research 91 (1): 220-229. 2015.
  •  66
    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,…Read more
  •  18
    Constraint and Freedom in the Common Law
    Philosophers' Imprint 15 1-27. 2015.
    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 …Read more
  •  46
    The purpose of this paper is to question some commonly accepted patterns of reasoning involving nonmonotonic logics that generate multiple extensions. In particular, I argue that the phenomenon of floating conclusions indicates a problem with the view that the skeptical consequences of such theories should be identified with the statements that are supported by each of their various extensions.
  •  28
    Right actions in perspective
    In Henrik Lagerlund, Sten Lindström & Rysiek Sliwinski (eds.), Modality Matters: Twenty-Five Essays in Honour of Krister Segerberg, Uppsala Philosophical Studies 53. pp. 53. 2006.
  • 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 philo…Read more
  •  75
    Argument construction and reinstatement in logics for defeasible reasoning
    Artificial Intelligence and Law 9 (1): 1-28. 2001.
    This paper points out some problems with two recent logical systems – one due to Prakken and Sartor, the other due to Kowalski and Toni – designedfor the representation of defeasible arguments in general, but with a specialemphasis on legal reasoning.
  •  116
    The Logic of Reasons
    with Shyam Nair
    In Daniel Star (ed.), Oxford Handbook of Reasons and Normativity, Oxford University Press. pp. 67-84. 2018.
    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…Read more
  •  16
    Review of Sven ove Hansson, The Structure of Values and Norms (review)
    Notre Dame Philosophical Reviews 2002 (6). 2002.
  •  57
    The purpose of this paper is to e»tahlish some connections between precedent-based reasoning as it is studied in the field of Artificial Intelligence and Law, particularly in the work of Ashley, and two other fields: deontic logic and nonmonotonic logic. First, a deontic logic is described that allows lor sensible reasoning in the presence of conflicting norms. Second, a simplified version of Ashley's account of precedent-based reasoning is reformulated within the framework of this deontic logi…Read more
  •  26
    Deontic Modals: Why Abandon the Classical Semantics?
    Pacific Philosophical Quarterly 95 (4): 424-460. 2014.
    I begin by reviewing classical semantics and the problems presented by normative conflicts. After a brief detour through default logic, I establish some connections between the treatment of conflicts in each of these two approaches, classical and default, and then move on to consider some further issues: priorities among norms, or reasons, conditional oughts, and reasons about reasons
  •  82
    This paper describes one way in which a precise reason model of precedent could be developed, based on Grant Lamond’s general idea that a later court is constrained to reach a decision that is consistent an earlier court’s assessment of the balance of reasons. The account provided here has the additional advantage of showing how this reason model can be reconciled with the traditional idea that precedential constraint involves rules, as long as these rules are taken to be defeasible