Von Wright’s “The Logic of Preference” revisited

Synthese, 2010

Preference is a key area where analytic philosophy meets philosophical logic. I start with two related issues: reasons for preference, and changes in preference, first mentioned in von Wright's book The Logic of Preference but not thoroughly explored there. I show how these two issues can be handled together in one dynamic logical framework, working with structured two-level models, and we investigate the resulting dynamics of reason-based preference in some detail. Next, we study the foundational issue of entanglement between preference and beliefs, and relate the resulting richer logics to belief revision theory and decision theory.

2009

In the last few years, preference logic and in particular, the dynamic logic of preference change, has suddenly become a live topic in my Amsterdam and Stanford environments. At the request of the editors, this article explains how this interest came about, and what is happening. I mainly present a story around some recent dissertations and supporting papers, which are found in the references. There is no pretense at complete coverage of preference logic (for that, see Hanson 2001) or even of preference change (Hanson 1995). Agency, information, and preference Human agents acquire and transform information in different ways: they observe, or infer by themselves, and often also, they ask someone else. Traditional philosophical logics describe part of this behaviour, the 'static' properties produced by such actions: in particular, agents' knowledge and belief at some given moment. But rational human activity is goal-driven, and hence we also need to describe agents' evaluation of different states of the world, or of outcomes of their actions. Here is where preference logic have come to describe what agents prefer, while current dynamic logics describe effects of their physical actions. In the limit, all these things have to come together in understanding even such a simple scenario as a game, where we need to look at what players want, what they can observe and guess, and which moves and long-term strategies are available to them in order to achieve their goals. There are two dual aspects to this situation. The static description of what agents know, believe, or prefer at any given moment has long been performed by standard systems of philosophical logic since the 1950s -of course, with continued debate surrounding the merits of particular proposals. But there is also the dynamics of actions and events that produce information and generate attitudes Overview This paper is mainly based on some recent publications in the Amsterdam environment over the last three years. Indeed, 'dynamics' presupposes an account of 'statics', and hence we first give a brief survey of preference logic in a simple modal format using binary comparison relations between possible worlds -on the principle that 'small is beautiful'. We also describe a recent alternative approach, where world preferences are generated from criteria or constraints. We show how to dynamify both views by adding explicit events that trigger preference change in the models, and we sketch how the resulting systems connect. Next, we discuss some entanglements between preference, knowledge and belief, and what this means for combined dynamic logics. On top of this, we also show how more delicate aspects of preference should be incorporated, such as its striking 'ceteris paribus' character, which was already central in Von Wright 1963. Finally, we relate our considerations to social choice theory and game theory. Preference is a very multi-faceted notion: we can prefer one individual object, or one situation, over another -but preference can also be directed toward kinds of objects or generic types of situation, often defined by propositions. Both perspectives make sense, and a bona fide 'preference logic' should do justice to all of them eventually. We start with a simple scenario on the object/world side, leaving other options for later. In this paper, we start with a very simple setting. Modal models M = (W, ≤, V) consist of a set of worlds W (but they really stand for any sort of objects that are subject to evaluation and comparison), a 'betterness' relation ≤ between worlds ('at least as good as'), and a valuation V for proposition letters at worlds (or, for unary properties of objects). In principle, the comparison relation may be different for different agents, but in what follows, we will suppress agent subscripts ≤ i whenever possible for greater readability. Also, we use the artificial term 'betterness' to stress that this is an abstract comparison relation, making no claim yet concerning the natural rendering of the intuitive term 'preference', about which some people hold passionate proprietary opinions. Still, this semantics is entirely natural and concrete. Just think of decision theory, where worlds (standing for outcomes of actions) are compared as to utility, or Here move is the union of all one-step move relations available to players, and * denotes the reflexive-transitive closure of a relation. The formula then says there is no alternative move to the BI-prescription at the current node all of whose outcomes would be better than the BI-solution. Thus, modal preference logic seems to go well with games. 3 But there are more examples. Already Boutilier 1994 observed how such a simple modal language can also define conditional assertions, normally studied per se as a complex new binary modality (Lewis 1973), and how one can then analyze their logic in standard terms. 4 For instance, in modal models with finite pre-orders (see below), the standard truth definition of a conditional A ⇒ B reads as 'B is true in all maximal A-worlds' -and this clause can be written as the following modal combination: with [] some appropriate universal modality. While this formula may look complex at first, the point is that the inferential behaviour of the conditional, including its well-known non-monotonic features, can now be completely understood via the base logic for the unary modalities, say, as a sub-theory of modal S4. Moreover, the modal language easily defines variant notions whose introduction seems a big deal in conditional logic, such as existential versions saying that each A-world sees at least one maximal A-world which is B. Of course, explicit separate axiomatizations of these defined notions retain an independent interest: but we now see the whole picture. 5 Constraints on betterness orders Which properties should a betterness relation have? Many authors like to work with total orders, satisfying reflexivity, transitivity, and connectedness. This is also common practice in decision theory and game theory, since 3 This, and also the following examples are somewhat remarkable, because there has been a widespread prejudice that modal logic is not very suitable to formalizing preference reasoning. 4 This innovative move is yet to become common knowledge in the logical literature. 5 There still remains the question of axiomatizing such defined notions per se: and that may be seen as the point of the usual completeness theorems in conditional logic. Also, Halpern 1997 axiomatized a defined notion of preference of this existential sort.

Erkenntnis, 1989

A possible world semantics for preference is developed. The remainder operator (_1.) is used to give precision to the notion that two states of the world are as similar as possible, given a specified difference between them. A general structure is introduced for preference relations between states of affairs, and three types of such preference relations are defined. It is argued that one of them, "actual preference", corresponds closely to the concept of preference in informal discourse. Its logical properties are studied and shown to be plausible.

2014

The normative realm involves deontic notions such as obligation or permission, as well as information about relevant actions and states of the world. This mixture is not static, given once and for all. Both information and normative evaluation available to agents are subject to changes with various triggers, such as learning new facts or accepting new laws. This paper explores models for this setting in terms of dynamic logics for information-driven agency. Our paradigm will be dynamic-epistemic logics for knowledge and belief, and their current extensions to the statics and dynamics of agents' preferences. Here the link with deontics is that moral reasoning may be viewed as involving preferences of the acting agent as well as moral authorities such as lawgivers, one's conscience, or yet others. In doing so we discuss a large number of themes: primitive 'betterness' order versus reason-based preferences (employing a model of 'priority graphs'), the entanglement of preference and informational attitudes such as belief, interactive social agents, and scenarios with long-term patterns emerging over time. Specific deontic issues considered include paradoxes of deontic reasoning, acts of changing obligations, and changing norm systems. We conclude with some further directions, as well as a series of pointers to related work, including different paradigms for looking at these same phenomena. This paper is an updated and revised version of a draft chapter for the Handbook of Deontic Logic, that was written originally in 2009. Given the recent increasing interest in our central themes of reason-based preference and preference dynamics, we are publishing the present version in the IF-COLOG Journal at the kind suggestion of Dov Gabbay. We are grateful to Guillaume Aucher and Davide Grossi for many useful comments and pointers, the majority of which will feed into the final chapter version when the Handbook appears.

journal of philosophical logic, 2011

This paper proposes a two-level modeling perspective which combines intrinsic ‘betterness’ and reason-based extrinsic preference, and develops its static and dynamic logic in tandem. Our technical results extend, integrate, and re-interpret earlier theorems on preference representation and update in the literature on preference change

Annals of Mathematics and Artificial Intelligence, 1993

The notion of preference is central to most forms of nonmonotonic reasoning. Shoham, in his dissertation, used this notion to give a single semantical point of view from which most nonmonotonic reasoning systems could be studied. In this paper, we study the notion of preference closely and devise a class of logics of preference that extract the logical core of the notion of preference. Earlier attempts have been largely unsuccessful, because of adoption as matters of logic of certain theory-specific preference principles such as asymmetry and transitivity. Soundness, completeness and decidability proofs for the logics are given. We define the notion of a preferential theory and reframe nonmonotonicity as a symbolic optimization problem where defaults are coded as preference criteria which place preference orders on the models of a first-order theory. We study the relationship between normal default theories and show the correspondence between models of extensions and optimal worlds. We give a preferential account of some forms of circumscription. The local nature of preference logic is contrasted with the global notion of normality and preference that is used by conditional logics of normality and cumulative inference operations. In related papers, we give a completely declarative semantics for the stable models of normal logic programs, a deontic logic based on preferences that is free of the anomalies of standard deontic logic, and extend Horn clause logic programming to impose partial orders on the bodies of clauses as declarative specification of the relaxation criteria for the truth-hood of the heads.

The normative realm involves deontic notions such as obligation or permission, as well as information about relevant ac- tions and states of the world. This mixture is not static, given once and for all. Both information and normative evaluation available to agents are subject to changes with various triggers, such as learn- ing new facts or accepting new laws. This paper explores models for this setting in terms of dynamic logics for information-driven agency. Our paradigm will be dynamic-epistemic logics for knowledge and belief, and their current extensions to the statics and dynamics of agents' preferences. Here the link with deontics is that moral rea- soning may be viewed as involving preferences of the acting agent as well as preferences of moral authorities such as lawgivers, one's conscience, or yet others. In our presentation of preference based agency, we discuss a large number of themes: primitive `betterness' order versus reason-based preferences (employing a model of `priority graphs'), the entanglement of preference and informational attitudes such as belief, interactive social agents, and scenarios with long-term patterns emerging over time. Speci c deontic issues considered in- clude paradoxes of deontic reasoning, acts of changing obligations, and changing norm systems. We conclude with some further direc- tions, such as multi-agency and games, plus pointers to related work, including di erent paradigms for looking at these same phenomena.

Introduction to Formal Philosophy, 2018

Preferences and choices have central roles in moral philosophy, economics, and the decision sciences in general. In a formal language we can express and explore the properties of preferences, choices, and their interrelations in a precise way, and uncover connections that are inaccessible without formal tools. In this chapter, the plausibility of different such properties is discussed, and it is shown how close attention to the logical details can help dissolve some apparent paradoxes in informal and semi-formal treatments.

2016

First, the paper discusses the extent to which preference change is a topic of normative rationality; it confirms as one main issue the economists ' search for a rational decision rule in cases in which the agent himself envisages to have chan ging / • preferences. Then it introduces so-called global decision models and shows that all the received economic models for dealing with preference change have that shape. The final seetion states two examples for global decision models, one with extrinsic, belief-induced and one with intrinsic preference change, and interprets each of them in two different scenarios in which ditlerent strategies are intuitively reasonable-the point being that global decision models cannot provide sufficient information for stating adequate decision rules. What the missing information might be is at least indicated at the end. In this brief paper I want to give a specific argument for the title thesis. It is an entirely negative one, as far as it goes, ...