EDITORS: Benz, Anton; Jaeger, Gerhard; Van Rooij, Robert TITLE: Game Theory and Pragmatics PUBLISHER: Palgrave Macmillan YEAR: 2005
Eric McCready, Department of English Language and Literature, Aoyama Gakuin University
SUMMARY
This book is the first booklength collection of papers available on the rapidly developing field of gametheoretic pragmatics, which uses techniques from game theory to characterize pragmatic phenomena. This collection includes 10 papers. The first, by the editors, is an introduction to game theory for linguists; since gametheoretic analysis involves techniques from utility and decision theory, the authors begin by giving a brief introduction to these areas, and move directly into a discussion of classical game theory. The chapter closes with the basics of evolutionary game theory. The chapter is extremely clear and aimed directly at linguists, and the reader that follows the discussion here is wellequipped to read the majority of the papers in the rest of the volume; conversely, the reader without something roughly equivalent to the background given in this chapter will have trouble understanding what is going on.
The second chapter, 'Saying and Meaning: Cheap Talk and Credibility', by Robert Stalnaker, considers the notion of credibility in communication by making use of signalling games. Stalnaker provides a way of characterizing credibility within this class of games and connects this characterization to the Gricean notion of intention in communication. This paper has several typos, most nonserious; the only one that caused real problems for me was a missing reference (to a paper by Robert Farrell), which was unfortunate. The reason for bringing this up is that it was atypical for the volume, which was in general nearly free of editing errors.
Next is Prashant Parikh's contribution, 'Pragmatics and Games of Partial Information.' In it, Parikh discusses his games of partial information as an extension of signalling games. He also suggests, in the latter part of his chapter, that these games can be used to model how solution concepts are selected (because in some situations certain equilibria may be better than others); this selection process might be modelled as a sequence of games, culminating in the game that models actual utterance interpretation.
The fourth chapter, Nicholas Allott's 'Game Theory and Communication,' discusses some assumptions of gametheoretic pragmatics from the perspective of relevance theory. Allott takes Parikh's (e.g. 2001) analysis as a starting point and argues that augmenting it with certain concepts of relevance theory improves the predictions of the model and also gives it broader application.
The above chapters are theoretical in nature and are largely concerned with foundational issues. The following chapters concern themselves with particular linguistic phenomena, and so are in a sense more empirically oriented. Chapter 5, by Robert van Rooij and Merlijn Sevenster, provides an analysis of 'risky speech', speech which is risky in the sense that it admits misunderstanding. Examples are underspecified utterances (extensively considered also by Parikh) and indirect speech acts, where the literal content is largely divorced from what the speaker intends the hearer to recover. The authors analyze such utterances by introducing a notion of risky play which comes with a cost. The end of the chapter extends this analysis to exhaustive interpretation.
Chapter 6, entitled 'Pragmatic Reasoning, Defaults and Discourse Structure,' is by Nicholas Asher and Madison Williams. [I should note for the record that one of these authors supervised my dissertation.  EMcC] These authors explore the question of how the pragmatic inferences stemming from semantic information develop: why do we reason about utterances in just the way we do? The answer, for the authors, comes in a dynamic coordination that arises through multiple game iterations. The way coordination is 'agreed' on is modelled in a dynamic version of Variable Frame Theory (Bacharach 1993).
Next, Anton Benz's chapter is on 'Utility and Relevance of Answers.' Benz begins by laying out the typology of question answers: exhaustive answers, mentionsome answers, and partial answers. He then provides a gametheoretic model for calculating the utility of a given answer; in this model, no notion of relevance must be assumed. Instead, agents are assumed to work to maximize expected payoffs: i.e. they are Bayesian utility maximizers. Benz then shows (convincingly in my view) that relevancebased measures cannot be sufficient to model answerhood. The basic reason is that pure relevance measures (at least as formulated up to now in the linguistic literature) make reference only to the preferences of a single agent. This is a very suggestive and interesting result.
In Chapter 8 Kris de Jaegher discusses 'GameTheoretic Grounding.' Here, de Jaegher shows that the basic notion of grounding (Traum 1994) can be given a gametheoretic characterization; he does this by making use of a simple communication game called the electronic mail game. This game introduces a coordination problem which agents can then work to solve. de Jaegher then shows that the various equilibria of (his variant of) this game corresponds to the different sorts of grounding shown to exist by Traum. This result is formally proved in the final section.
Chapter 9 'A Game Theoretic Approach to the Pragmatics of Debate' by Jacob Glazer and Ariel Rubenstein describes what one would guess from the title. Specifically, Glazer and Rubenstein set out to explain what strategies are used by listeners to judge the winner of a debate. The authors first show that the form of the argument makes a difference; second, they show that no method is foolproof. The end of the paper makes a specific connection to language, showing that the strategy space depends in part on the form of the language used to specify the solutions.
The last paper in the volume is 'On the Evolutionary Dynamics of MeaningWord Associations' by Tom Lenaerts and Bart de Vylder. This chapter is the only one that makes use of evolutionary game theory (EGT). Here it is used to show how particular meanings can be fixed to particular signals, in the context of an experiment involving a sequence of 'naming games' in which one player picks a signal from a given set to describe a meaning and the other player tries to recover the meaning. The authors show that, given the right kind of replicator equations, meanings are consistently associated with signals in a successful way. This chapter requires more mathematical sophistication than the others, which is perhaps a result of the use of EGT. The reader with no experience of game theory (or without proficiency in calculus) might have a difficult time understanding some of the exposition, even after reading the introductory chapter. I think this is the only chapter that has this property, again probably because of the use of EGT.
EVALUATION
This book can only be described as exciting. The gametheoretic approach to pragmatics is an extremely interesting and useful one, and is one that is really only beginning to be explored in detail. But one can already find analyses of such phenomena as Gricean inference and exhaustification within the framework; this sort of data has in the past resisted formalization, but serious progress is being made. One of the reasons this book is welcome is therefore that it collects the state of the art (or at least a large subset thereof) into a single place. One other reason is the introduction: for people without a background in game theory, which is probably most linguists, it is extremely useful to have an introduction to game theory around that takes the concerns of linguists into account. Another nice feature of the introduction is that it is almost completely selfcontained: unlike, for instance, game theory texts aimed at economists, no special background in mathematics is assumed beyond an understanding of basic formal logic. Thus the book is worth acquiring for the introduction alone. But I don't mean to sell the papers short by any means. They all present interesting results, as one can gather from the summaries above, although these results come on a number of different levels. As one might expect from an emerging field of study, there is not yet a consensus about what the basic conceptualization of the field should be; the first papers in the volume perhaps speak to these concerns more than they do to the analysis of empirical data. From this perspective the middle group of papers might be more useful for the working pragmaticist. But I would recommend this book very highly to anyone interested in this recent approach to pragmatics, or to formal accounts of pragmatic phenomena in general.
REFERENCES
Bacharach, M. 1993. Variable universe games. In K. Binmore, A. Kirman and P. Tani, eds., Frontiers of Game Theory, Cambridge MA: MIT Press.
Parikh, P. 2001. The Use of Language. Stanford: CSLI.
Traum, D. R. 1994. A Computational Theory of Grounding in Natural Language Conversation. Ph.D Thesis, University of Rochester.
