•  586
    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
  •  215
    Reasons as Defaults
    Philosophers' Imprint 7 1-28. 2007.
    The goal of this paper is to frame a theory of reasons--what they are, how they support actions or conclusions--using the tools of default logic. After sketching the basic account of reasons as provided by defaults, I show how it can be elaborated to deal with two more complicated issues: first, situations in which the priority relation among defaults, and so reasons as well, is itself established through default reasoning; second, the treatment of undercutting defeat and exclusionary reasons. F…Read more
  •  172
    Reasoning with moral conflicts
    Noûs 37 (4). 2003.
    Let us say that a normative conflict is a situation in which an agent ought to perform an action A, and also ought to perform an action B, but in which it is impossible for the agent to perform both A and B. Not all normative conflicts are moral conflicts, of course. It may be that the agent ought to perform the action A for reasons of personal generosity, but ought to perform the action B for reasons of prudence: perhaps A involves buying a lavish gift for a friend, while B involves depositing a c…Read more
  •  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
  •  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
  •  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
  •  80
    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
  •  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.
  •  72
    Defaults with Priorities
    Journal of Philosophical Logic 36 (4): 367-413. 2007.
  •  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
  •  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
  •  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
  •  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 ...
  •  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
  •  51
    An appreciation of John Pollock's work on the computational study of argument
    with Henry Prakken
    Argument and Computation 3 (1). 2012.
    John Pollock (1940?2009) was an influential American philosopher who made important contributions to various fields, including epistemology and cognitive science. In the last 25 years of his life, he also contributed to the computational study of defeasible reasoning and practical cognition in artificial intelligence. He developed one of the first formal systems for argumentation-based inference and he put many issues on the research agenda that are still relevant for the argumentation community…Read more
  •  46
    A factor-based definition of precedential constraint
    with Trevor J. M. Bench-Capon
    Artificial Intelligence and Law 20 (2): 181-214. 2012.
    This paper describes one way in which a precise reason model of precedent could be developed, based on the general idea that courts are constrained to reach a decision that is consistent with the assessment of the balance of reasons made in relevant earlier decisions. 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. The…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.
  •  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..
  •  41
    Requirements, Oughts, Intentions
    Philosophy and Phenomenological Research 91 (1): 220-229. 2015.
  •  35
    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-
  •  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.
  •  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.
  •  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
  •  26
    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
  •  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
  •  22
    Epistemic Oughts in Stit Semantics
    Ergo: An Open Access Journal of Philosophy 6. 2019.