A pedagogical proof of Arrow's Impossibility Theorem

In this note I consider a simple proof of Arrow's Impossibility Theorem (Arrow 1963). I start with the case of three individuals who have preferences on three alternatives. In this special case there are 13³=2197 possible combinations of the three individuals' rational preferences. However, by considering the subset of linear preferences, and employing the full strength of the IIA axiom, I reduce the number of cases necessary to completely describe the SWF to a small number, allowing an elementary proof suitable for most undergraduate students.  This special case conveys the nature of Arrow's result. It is well known that the restriction to three options is not really limiting (any larger set of alternatives can be broken down into triplets, and any inconsistency within a triplet implies an inconsistency on the larger set). However, the general case of n≥3 individuals can be easily considered in this framework, by building on the proof of the simpler case. I hope that a motivated student, having mastered the simple case of three individuals, will find this extension approachable and rewarding.  This approach can be compared with the traditional simple proofs of Barberà (1980); Blau (1972); Denicolò (1996); Fishburn (1970); Kelly (1988); Mueller (1989); Riker and Ordeshook (1973); Sen (1979, 1986); Suzumura (1988), and Taylor (1995). Received: 5 January 1999/Accepted: 10 December 1999     

The structure of fuzzy preferences: Social choice implications

It has been shown that, with an alternative factorization of fuzzy weak preferences into symmetric and antisymmetric components, one can prove a fuzzy analogue of Arrow's Impossibility Theorem even when the transitivity requirements on individual and social preferences are very weak. It is demonstrated here that the use of this specification of strict preference, however, requires preferences to also be strongly connected. In the absence of strong connectedness, another factorization of fuzzy weak preferences is indicated, for which nondictatorial fuzzy aggregation rules satisfying the weak transitivity requirement can still be found. On the other hand, if strong connectedness is assumed, the fuzzy version of Arrow's Theorem still holds for a variety of weak preference factorizations, even if the transitivity condition is weakened to its absolute minimum. Since Arrow's Impossibility Theorem appeared nearly half a century ago, researchers have been attempting to avoid Arrow's negative result by relaxing various of his original assumptions. One approach has been to allow preferences – those of individuals and society or just those of society alone – to be “fuzzy.” In particular, Dutta [4] has shown that, to a limited extent, one can avoid the impossibility result (or, more precisely, the dictatorship result) by using fuzzy preferences, employing a particularly weak version of transitivity among the many plausible (but still distinct) definitions of transitivity that are available for fuzzy preferences. Another aspect of exact preferences for which the extension to the more general realm of fuzzy preferences is ambiguous is the factorization of a weak preference relation into a symmetric component (indifference) and an antisymmetric component (strict preference). There are several ways to do this for fuzzy weak preferences, all of them equivalent to the traditional factorization in the special case when preferences are exact, but quite different from each other when preferences are fuzzy (see, for example, [3]). A recent paper in this journal [1], by A. Banerjee, argues that the choice of definitions for indifference and strict preference, given a fuzzy weak preference, can also have “Arrovian” implications. In particular, [1] claims that Dutta's version of strict preference presents certain intuitive difficulties and recommends a different version, with its own axiomatic derivation, for which the dictatorship results reappear even with Dutta's weak version of transitivity. However, the conditions used to derive [1]'s version of strict preference imply a restriction on how fuzzy the original weak preference can be, namely, that the fuzzy weak preference relation must be strongly connected. Without this restriction, I will show that the rest of [1]'s conditions imply yet a third version of strict preference, for which Dutta's possibility result under weak transitivity still holds. On the other hand, if one accepts the strong connectedness required in order for it to be valid, I show that [1]'s dictatorship theorem can in fact be strengthened to cover any version of transitivity for fuzzy preferences, no matter how weak, and further, that this dictatorship result holds for any “regular” formulation of strict preference, including the one originally used by Dutta. Received: 13 May 1996 / Accepted: 13 January 1997     

Independent Decisiveness and the Arrow theorem

I show that the condition of Independence of Irrelevant Alternatives in Arrow's impossibility theorem can be weakened into Relational Independent Decisiveness. The condition of Relational Independent Decisiveness is essentially a translation of Sen's Independent Decisiveness into the traditional Arrovian framework. I also show by example that Relational Independent Decisiveness is indeed weaker than Arrow's Independence of Irrelevant Alternatives. Received: 30 October 1996 / Accepted: 22 May 1997     

Independence of irrelevant interpersonal comparisons

Arrow's independence of irrelevant alternatives (IIA) condition makes social choice depend only on personal rather than interpersonal comparisons of relevant social states, and so leads to dictatorship. Instead, a new independence of irrelevant interpersonal comparisons (IIIC) condition allows anonymous Paretian social welfare functionals such as maximin and Sen's leximin, even with an unrestricted preference domain. But when probability mixtures of social states are considered, even IIIC may not allow escape from Arrow's impossibility theorem for individuals' (ex-ante) expected utilities. Modifying IIIC to permit dependence on interpersonal comparisons of relevant probability mixtures allows Vickrey-Harsanyi utilitarianism. Thus, if we wish to go beyong the comparisons that are possible using only the [pareto] principle of the new welfare economics, the issue is not whether we can do so without making interpersonal comparisons of satisfactions. It is rather, what sorts of interpersonal comparisons are we willing to make. Unless the comparisons allowed by Arrow's Condition 3 [independence of irrelevant alternatives] could be shown to have some ethical priority, there seems to be no reason for confining consideration to this group.Hildreth (1953, p 91)     

The free triple assumption

Many impossibility results, like Arrow's Theorem, can be strengthened by using a domain constraint that is substantially weaker than the usual domain condition.     

Arrow's Theorem with a fixed feasible alternative

Arrow's Theorem, in its social choice function formulation, assumes that all nonempty finite subsets of the universal set of alternatives is potentially a feasible set. We demonstrate that the axioms in Arrow's Theorem, with weak Pareto strengthened to strong Pareto, are consistent if it is assumed that there is a prespecified alternative which is in every feasible set. We further show that if the collection of feasible sets consists of all subsets of alternatives containing a prespecified list of alternatives and if there are at least three additional alternatives not on this list, replacing nondictatorship by anonymity results in an impossibility theorem.Most of the research for this article was completed while we were participants in the Public Choice Institute held at Dalhousie University during the summer of 1984. We wish to record here our thanks to the Institute Director, E.F. McClennen, and its sponsors, the Council for Philosophical Studies, the U.S. National Science Foundation, and the Social Science and Humanities Research Council of Canada. We are grateful to our referees for their comments and the Center for Mathematical Studies in Economics and Management Science at Northwestern University, where Weymark was a visitor during 1985–86, for secretarial assistance.     

Connecting and resolving Sen's and Arrow's theorems

It is shown that the source of Sen's and Arrow's impossibility theorems is that Sen's Liberal condition and Arrow's IIA counter the critical assumption that voters have transitive preferences. But if the procedures are not permitted to treat the transitivity of individual preferences as a valued input, then we cannot expect rational outputs. Once this common cause for these perplexing conclusions is understood, these classical conclusions end up admitting quite benign interpretations where it becomes possible to propose several resolutions. Received: 2 April 1996 / Accepted: 15 October 1996     

Generalized condorcet-winners for single peaked and single-plateau preferences

When preferences are single peaked the choice functions that are independent of irrelevant alternatives both in Nash's and in Arrow's sense are characterized. They take the Condorcet winner of the n individual peaks plus at most n-1 fixed ballots (phantom voters). These choice functions are also coalitionally strategy-proof.Next the domain of individual preferences is enlarged to allow for singleplateau preferences: again, Nash's IIA and Arrow's IIA uniquely characterize a class of generalized Condorcet winners choice functions. These are, again, coalitionally strategy-proof.     

Rational budgeters in the theory of social choice

The purpose of this paper is to explore duality in the theory of social choice. As application Arrow's Impossibility Theorem and another impossibility theorem using the notion of positive responsiveness are chosen. It will be seen that we can establish notions and theorems which are symmetric to the original ones. However, if we establish impossibility theorems when rational behaviour is described by budget correspondences and not by choice correspondences, we need not assume that every subset of X (a family of alternatives) with cardinality 2 is a budget set. Therefore the dual theorems also may hold for families of competitive budget sets. It will also be shown that although the underlying preferences on X need not be acyclic, local decisiveness on budget sets may lead to global decisiveness on these sets.     

On metrically conservative societies

In this paper, social choice theory is considered from the standpoint of social change. Various metrics (in a discrete setting) are introduced to measure changes in individual and collective preferences, and a society is said to be metrically conservative if social change does not exceed total individual changes. Arrow's IIA Axiom is found to be intimately related to a very restrictive metrical condition called metrical ultraconservatism. Strong characterization theorems are proved for metrically ultraconservative societies. A natural relaxation is the condition of metrical conservatism. We show that metrically conservative societies exist, and the number of possibilities can in fact grow exponentially with the population. But when the metrical condition is placed into the more specific socio-economic context of strict preference orderings, normative restrictions appear. One is the constitutional protection against the election of a dictator; another is the nonexistence of metrically conservative stable matchings, in the sense of Gale-Shapley. Some similar questions have been raised in continuous social choice theory, but the conclusions are quite different. We also consider the effect of an increasing population on the average rate of social change.The author is grateful to Dr. T.M. Tang for first drawing his attention to Arrow's General Possibility Theorem, to Professors Robert M. Anderson, Kenneth J. Arrow, and an anonymous referee for many valuable suggestions, and to Dr. W.Y. Poon for pointing out an important reference. This work was done when the author was at the University of California at Berkeley and formed part of his Berkeley Ph.D. dissertation. The views expressed here are the author's, and not necessarily those of AT&T Bell Laboratories.     

Social choice with analytic preferences

Arrow's axioms for social welfare functions are shown to be inconsistent when the set of alternatives is the nonnegative orthant in a multidimensional Euclidean space and preferences are assumed to be either the set of analytic classical economic preferences or the set of Euclidean spatial preferences. When either of these preference domains is combined with an agenda domain consisting of compact sets with nonempty interiors, strengthened versions of the Arrovian social choice correspondence axioms are shown to be consistent. To help establish the economic possibility theorem, an ordinal version of the Analytic Continuation Principle is developed. Received: 4 July 2000/Accepted: 2 April 2001     

Cost range and the stable network structures

The work of this paper concerns with the stable structures in different cost range identified by Doreian in his paper [Doreian, P., 2006. Actor network utilities and network evolution. Social Networks 28, 137–164]. We point out some problems with his Theorem 4 and present our corrections to that theorem.     

The pre-history of Kenneth Arrow's social choice and individual values

The purpose of this article is to give an historical sense of the intellectual developments that determined the form and content of Kenneth Arrow's path-breaking work published in 1951. One aspect deals with personal influences that helped shape Arrow's own thinking. A second aspect is concerned with the early history of the general theory of relations, which is mainly centered in the nineteenth century, and also with the essentially independent modern development of the axiomatic method in the same time period. Arrow's use of general binary relations and of axiomatic methods to ground, in a clear mathematical way, his impossibility theorem marks a turning point in welfare economics, and, more generally, in mathematical economics.     

Arrow's theorem for economic environments and effective social preferences

Arrow's impossibility theorem has been proved for the realm of private goods and economic preferences by Border and by Bordes and Le Breton. However, their proofs require the exclusion of the zero vector from the commodity space. This paper proves the impossibility theorem for the entire allocation space and the classical domain of economic preferences by adding effectiveness to Arrow's hypothesis. Social preference is effective if every nonempty compact set contains at least one socially optimal allocation.Financial support from the Social Sciences and Humanities Research Council (Canada) is gratefully acknowledged. The comments of an anonymous referee were much appreciated. The author assumes responsibility for any errors.     

Sequential path independence and social choice

Arrow's general impossibility theorem shows that every Paretian social choice function which satisfies independence of irrelevant alternatives and the Axiom of Sequential Path Independence is necessarily dictatorial. It is shown that the existence of a dictator can be established without invoking full path independence. We propose an axiom of weak path independence of a sequential choice procedure. This axiom turns out to be independent of the factor that is critical in obtaining dictatorship or oligarchy results in the choice theoretic framework.     

Harsanyi's Aggregation Theorem: multi-profile version and unsettled questions

Harsanyi's Aggregation Theorem states that if the individuals' as well as the moral observer's utility functions are von Neumann-Morgenstern, and a Pareto condition holds, then the latter function is affine in terms of the former. Sen and others have objected to Harsanyi's use of this result as an argument for utilitarianism. The present article proves an analogue of the Aggregation Theorem within the multi-profile formalism of social welfare functionals. This restatement and two closely related results provide a framework in which the theorem can be compared with well-known characterisations of utilitarianism, and its ethical significance can be better appreciated. While several interpretative questions remain unsettled, it is argued that at least one major objection among those raised by Sen has been answered.The author is grateful to V. Barham, J. Broome, M. Fleurbaey, D. Hausman, S. Kolm, J. Roemer, and P. Suppes, for useful discussions and suggestions. Special thanks are due to C. d'Aspremont, N. McClennen, J. Weymark, and an anonymous referee for detailed comments on an earlier version. The usual caveat applies. The author also gratefully acknowledges financial support from the SPES programme of the Union Européenne.     

Wilson's theorem for economic environments and continuous social preferences

Wilson's generalization of Arrow's impossibility theorem has been proved for the realm of private goods and economic preferences by Border and by Bordes and Le Breton. However, their proofs require the exclusion of the zero vector from the commodity space. This paper assumes continuity of social preference to obtain the impossibility theorem for the entire allocation space, even if the society is infinite. A simple corollary reveals that there is some individual who is assigned the zero consumption vector at every social optimum whenever the social welfare function is nonnull and nonimposed, and satisfies Arrow's independence axiom and continuity and transitivity of social preference.Financial support from the Social Sciences and Humanities Research Council is gratefully acknowledged, as are the suggestions of Charles Plott and an anonymous referee. The author assumes responsibility for any errors.     

An axiomatic approach to intergenerational equity

We present a set of axioms in order to capture the concept of equity among an infinite number of generations. There are two ethical considerations: one is to treat every generation equally and the other is to respect distributive fairness among generations. We find two opposite results. In Theorem 1, we show that there exists a preference ordering satisfying anonymity, strong distributive fairness semiconvexity, and strong monotonicity. However, in Theorem 2, we show that there exists no binary relation satisfying anonymity, distributive fairness semiconvexity, and sup norm continuity. We also clarify logical relations between these axioms and non-dictatorship axioms. Received: 30 August 2000/Accepted: 18 March 2002 This paper is based on Chapt. 4 of my Masters Thesis [15] submitted to Kobe University, and won the Kanematsu Fellowship from the Research Institute for Economics and Business Administration of Kobe University in May 2001. I am grateful to Jun Iritani for helpful discussions and encouragement, two anonymous referees of this journal, three anonymous referees of the Kanematsu Fellowship, Eiichi Miyagawa, Noritsugu Nakanishi, Nguyen Huu Phuc, Hiroo Sasaki, Koji Shimomura, William Thomson, and Toyoaki Washida for detailed comments. I also thank participants at the spring meeting of Japanese Economic Association at Yokohama City University in May 2000, at the annual meeting of the Society for Environmental Economics and Policy Studies in Tsukuba in September 2000, and at the Kanematsu Fellowship Seminar at Kobe University in May 2001 for valuable comments.     

Complete characterization of functions satisfying the conditions of Arrow’s theorem

Arrow??s theorem implies that a social welfare function satisfying Transitivity, the Weak Pareto Principle (Unanimity), and Independence of Irrelevant Alternatives (IIA) must be dictatorial. When non-strict preferences are also allowed, a dictatorial social welfare function is defined as a function for which there exists a single voter whose strict preferences are followed. This definition allows for many different dictatorial functions, since non-strict preferences of the dictator are not necessarily followed. In particular, we construct examples of dictatorial functions which do not satisfy Transitivity and IIA. Thus Arrow??s theorem, in the case of non-strict preferences, does not provide a complete characterization of all social welfare functions satisfying Transitivity, the Weak Pareto Principle, and IIA. The main results of this article provide such a characterization for Arrow??s theorem, as well as for follow up results by Wilson. In particular, we strengthen Arrow??s and Wilson??s result by giving an exact if and only if condition for a function to satisfy Transitivity and IIA (and the Weak Pareto Principle). Additionally, we derive formulae for the number of functions satisfying these conditions.     

Positional independence in preference aggregation

If, for strict preferences, a unique choice function (CF) is used to aggregate preferences position-wise then the resulting social welfare function (SWF) is dictatorial. This suggests that the task performed by non-dictatorial SWFs must be “more complex” than just selecting an alternative from a list using a single criterion. This is because the information required by non-dictatorial SWFs to aggregate preferences cannot be compressed into a CF. It is also shown that the attempt to reduce the working of a SWF to the working of a CF involves the adoption of certain positional requirements, whose relationship with the conditions in Arrow's theorem is established. Received: 28 May 2001/Accepted: 25 March 2002 My deepest gratitude to Donald G. Saari, who rescued this paper from the worst fate, and to the referee, who showed the escape route.