Social Choice and Individual Values

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Social Choice and Individual Values is a book written by Kenneth Arrow first published in 1951. Narrowly interpreted, the "social choice" in the title is Arrow's formalization of how "social values" might be represented. The book and the ”General Possibility Theorem” in it created social choice theory, a rigorous melding of social-ethics and voting theory with an economic flavor. Intuitively, each 'social choice' corresponds to a feasible set of laws passed by a "vote" ('set of orderings') under the 'constitution' even if each individual did not vote in favor of all the laws.

Arrow's theorem shows that, absent restrictions on either individual preferences or neutrality of the constitution as to feasible alternatives, there exists no social choice rule that satisfies a set of seemingly plausible requirements. The result is a generalization and extension of the voting paradox, which shows that majority voting may fail to yield a stable outcome.

Contents

1 Introduction
2 Terminology
3 Conditions and theorem
4 Proof
5 Conclusion, challenge, and aftereffects
6 See also
7 References
8 External links

Introduction

The Introduction contrasts voting in the political realm and markets in the economic realm with dictatorship and social convention (such as from a religious code). These are all ways of making social decisions. But voting and markets facilitate social choice in a sense, as dictatorship and convention limit it. The former amalgamate possibly differing tastes to make a social choice. The concern is with formal aspects of generalizing such choices. In this respect it is comparable to analysis of the voting paradox from accepting majority rule as a value. Arrow asks whether other methods of taste aggregation (whether by voting or markets), using other values, remedy the problem or are satisfactory in other ways. Here logical consistency is one check on acceptability of all the values. To answer the questions, he proposes removing the distinction between voting and markets in favor of a more general category of collective social choice.

The analysis uses ordinal rankings of individual choice to represent behavioral patterns. Cardinal measures of individual utility and, a fortiori, interpersonal comparisons of utility are avoided on grounds that such measures are unnecessary to represent behavior and depend on mutually incompatible value judgments.

Following Abram Bergson, whose formulaton of a social welfare function launched ordinalist welfare economics, Arrow avoids locating a social good as independent of individual values. His approach locates social values in actions from social-decision rules ('conditions') using individual values as input. Then 'social values' means "nothing more than social choices."

Topics implicated along the way include game theory, the compensation principle in welfare economics, extended sympathy, Leibniz's principle, log rolling, and similarity of social judgments through single-peaked preferences, Kant’s categorical imperative, or the decision process.

Terminology

The book defines a few terms and logical symbols used thereafter and their applied empirical interpretation. Key among these is the "vote" ('set of orderings') of the society (more generally "collectivity") comprised of individuals (“voters” here) in the following form:

Voters, a finite set with at least two members, indexed as 1, 2, ..., i, ..., n.
*Commodities, the objects of choice (things that voters might want, goods and services), including private and collective (municipal services, statecraft, etc.).
**A social state, a complete description (representable as a vector) of a (conceivable) bundle of 'commodities' as to quantity and distribution among voters, labor supplied by each voter, and resources used in each productive activity.
***The set of social states, the set of all 'social states', indexed as x, y, z, . . , with at least three members.
****An ordering, a ranking by a voter of all 'social states' from more to less preferred, including possible ties.
*****The set of 'orderings', the set of all n orderings, one ordering per voter.

Example: Three voters and three states . Given the three states, there are 13 logically possible orderings (allowing for ties).* Since each of the individuals may hold any of the orderings, there are 13*13*13 = 2197 possible "votes" (sets of orderings). A well-defined social-decision rule selects the social state (or states, in case of tie) corresponding to each of these "votes."

* Namely, from top to bottom for each possible ranking and with 'T's indexing ties:

x y z    x   y T z  (x T y z repeats
y x z    y T x   z   y T x z, so is omitted, etc.)

z x y    z   x T y
x z y    x T z   y

y z x    y   z T x
z y x    z T y   x    x T y T z

The ordering of each voter ranks social states, including the distribution of commodities (possibly based on equity, by whatever metric, or any other consideration), not merely direct consumption by that voter. So, the ordering is an "individual value," not merely, as in earlier analysis, a purely private "taste." Arrow notes that the distinction is not sharp. Resource allocation is specified in the production of each social state in the ordering.

The comprehensive character of commodities, the set of social states, and the set of orderings was noted by early reviewers.

The 2 properties that define any ordering of the set of objects in question (all social states here) are:

connectedness (completeness): All the objects in the set are included in the ranking (no "undecideds" nor "abstentions") and

transitivity: If, for any objects x, y, and z in the set, x is ranked at least as high as y and y is ranked at least as high as z, then x is ranked at least as high as z.

A standard indifference-curve map for an individual has these properties and so is an ordering. Each ray from the origin ranks (conceivable) commodity bundles from least preferred on up (no ties in the ranking). Each indifference curve ranks commodity bundles as equally preferred (all ties in the ranking).

The earlier definition of an ordering implies that any given ordering entails 1 of 3 responses on the "ballot" as between any pair of social states (x, y): better than, as good as, or worse than (in preference satisfaction). (Here "as good as" is an "equally-ranked," not a "don't know," relation.)

The denotations of these 3 "ballot" options are respectively:

x P y (x preferred to y)

x I y (voter indifferent to x and y)

y P x (y preferred to x).

It is convenient for deriving implications to compact the first 2 of these options on the ballot to 1, an "at least as good as" relation, denoted R:

x R y: either x preferred to y or x indifferent to y).

The above 2 properties of an ordering are then axiomatized as:

connectedness: For all (the objects of choice in the set) x and y, either x R y or y R x.

transitivity: For all x, y, and z, x R y and y R z imply x R z.

(Thus, alternation ('or') and conjunction ('and') of R relations represent both the properties of an ordering for all the objects of choice.)

The I and P relations are then defined as:

x I y: x R y and y R x (x as good as y means x at least as good as y and vice versa).

x P y: not y R x (y R x includes 1 of 2 options. Negating that option leaves only x P y, the third of the original 3 options, on the ballot.)

From this, conjunction ('and') and negation ('not') of mere pairwise R relations can (also) represent all the properties of an ordering for all the objects of choice. Hence, the following shorthand.

An ordering of a voter is denoted by R. That ordering of voter i is denoted with a subscript as [R_i].

If voter i changes orderings, primes distinguish the first and second, say [R_i] compared to [R_i]' . The same notation can apply for 2 different hypothetical orderings of the same voter.

The interest of the book is in amalgamating sets of orderings. This is accomplished through a 'constitution'.

A constitution (or social welfare function) is a voting rule mapping each (of at least 1) set of orderings onto a social ordering, a corresponding ordering of the set of social states.

A social ordering in a constitituion is denoted R. (Context or a subscript distinguishes a voter ordering R from the same symbol for a social ordering.)

For any 2 social states x and y of a given social ordering R:

x P y is "social preference" of x over y (x is selected over y by the rule).

x I y is "social indifference" between x and y (both are ranked the same).

x R y is either "social preference" of x over y or "social indifference" between x and y.

A social ordering applies to each ordering in the set of orderings (hence the "social" part). This is so regardless of (dis)similarity between the social ordering and any or all the orderings in the set. But Arrow places the constitution in the context of ordinalist welfare economics, which attempts to aggregate different tastes in a coherent, plausible way.
The social ordering for a given set of orderings as to the set of social states is analogous to an indifference-curve map for an individual as to the set of commodity bundles. There is no necessary interpretation from this that "society" is just a big voter. Still, the relation of a set of voter orderings to the outcome of the voting rule, whether a social ordering or not, is a focus of the book.

Arrow shows how to go from the social ordering for a given set of orderings to a particular 'social choice' by specifying:

the environment, S: the subset of social states that is (hypothetically) available (feasible as to resource quantity and productivity), not merely conceivable.

The social ordering then selects the top-ranked social state(s) from the subset as the 'social choice'.

In demand theory, the subset corresponds to the set of commodity bundles on or inside the budget constraint for an individual as to the set of commodity bundles. The consumer's top choice is at the highest indifference curve on the budget constraint.

The formal generalization is:

the social choice function: the function mapping each environment S of available social states (at least 2) for any given set of orderings (and corresponding social ordering R) to the social choice, the top-ranked social state(s) for that environment and that set of orderings.

The social choice function is denoted C(S). Consider an environment that has just 2 social states, x and y. S is denoted [x, y], and the social choice function is C([x, y]). Suppose x is the only top-ranked social state. Then C([x, y]) = , the social choice. If x and y are instead tied, C([x, y]) = .

The next section invokes the following. Let R and R' stand for different social orderings corresponding to different sets of orderings. If R and R' for the same environment S map to the same social choice(s), the relation of the identical social choices for R and R' is represented as: C(S) = C'(S).

Conditions and theorem

A constitution might seem to be a promising alternative to dictatorship and vote-immune social convention or external control. Arrow describes the connectedness of a social ordering as requiring only that some social choice be made from any environment of available social states. Since some social state will prevail, this is hard to deny (especially with no place on the ballot for abstention). The transitivity of a social ordering has an advantage over requiring unanimity (or much less) to change between social states if there is a maladapted status quo (that is, one subject to "democratic paralysis"). Absent deadlock, transitivity crowds out any reference to the status quo as a privileged default blocking the path to a social choice.

Arrow proposes conditions to constrain the social ordering(s) of the constitution. The conditions, presented below, can be interpreted as general, practically necessary, or apparently reasonable.

1. Universal (unrestricted) domain U (subsequently so called): Every logically possible set of orderings maps to its own social ordering.

Each voter is permitted by the constitution to rank the set of social states in any order, though with only one ordering per voter for a given set of orderings.

Arrow refers to a constitution satisfying this condition as collective rationality. It can be compared to the rationality of a voter ordering. But the prescription of collective rationality, which Arrow proposes, is distinct from the descriptive use of a voter ordering, which he deploys. Hence, his denial at the end of the book that collective rationality is "merely an illegitimate transfer from the individual to society."

2. Independence of irrelevant alternatives I: Let S be a subset of hypothetically available (not merely conceivable) social states, say x and y, from the set of social states. Let [R_1], ..., [R_n] and [R_1]' , ..., [R_n]' be any 2 sets of orderings with the following property: For every voter i , the ranking of x and y in S is (by construction) the same. (Different voters could still have different rankings of the 2 social states.) Then the subset S for each of the 2 sets of orderings maps to an identical social choice.

Condition I: Let S be a subset of hypothetically available social states from the set of social states. Let [R_1], ..., [R_n] and [R_1]' , ..., [R_n]' be any 2 sets of orderings with the following property: For all pairs of x and y in S, x [R_i] y if and only if x [R_i]' y, for every voter i. Then the corresponding social choice functions map to an identical social choice: C(S) = C'(S).

This identical mapping happens even with differences in rankings of any voter between the two sets of orderings outside that subset of social states. Consider a hypothetical “run-off election” between say only 2 available social states. The social choice is associated with the sets of rankings for that subset, not with rankings of unavailable social states beyond the subset. Thus, that social choice for the subset is unaffected by say a change in orderings only beyond the subset.

Arrow describes this condition as an extension of ordinalism with its emphasis on prospectively observable behavior (based on availability of the subset in question). He ascribes practical advantage to the condition from "every known electoral system" satisfying it.

3. The (weak) Pareto principle P: For any x and y in the set of social states, if all prefer x over y, then x is socially selected over y

Condition P: For any x and y in the set of social states, if for every voter i x [P_i] y, then x P y.

As Sen (ch. 3.4) suggests, Pareto unanimity can override a decision rule (in the form of a convention) by selecting a certain social state that is otherwise vote-immune.

The conditions, particularly the second and third, may seem minimal, but jointly they are harsh:

Arrow’s Theorem: The 3 conditions of the constitution imply a dictator who prevails as to the social choice whatever that individual's preference and those of all else.

An alternate statement of the theorem adds the following condition to the above:

4. Nondictatorship D: No voter in the society is a dictator. That is, there is no voter i in the society such that for every set of orderings in the domain of the constitution and every pair of distinct social states x and y, if voter i strictly prefers x over y, x is socially selected over y.

such that for every set of orderings in the domain of the constitution and every pair of social states x and y, x [P_i] y implies x P y. |}

Arrow's Theorem: The constitution is impossible, that is, the 4 conditions of a constitution imply a contradiction.

Proof

The proof is in two parts. The first part considers if someone's ordering prevails ('is decisive') as to the social choice for some pair of social states no matter what the orderings of that voter and those of others. It is shown that the voter would prevail similarly for every pair of social states and thus all social states. So, the voter would be a dictator. Thus, avoiding dictatorship requires postulating that no one would so prevail for some pair of social states. The second part shows that, given the first 3 conditions, someone would so prevail for some pair of social states. This contradicts the postulate (and thus nondictatorship) and so proves the theorem.

Conclusion, challenge, and aftereffects

The book proposes some apparently reasonable conditions for a "voting" rule, in particular, a 'constitution', to make consistent, feasible social choices in a welfarist context. But any constitution that allows dictatorship requires it, and any constitution that requires nondictatorship is contradictory. Hence, the paradox of social choice.

The set of conditions across different possible votes of values refined welfare economics and differentiated Arrow's constitution from the pre-Arrow social welfare function. Thus, dictatorship within a vote and across every possible vote on social alternatives makes redundant a pre-Arrow external agent or an official intent on implementing the values of others in the society through the constitution. The remaining alternative, nondictatorship, excludes a pre-Arrow social welfare function as a consistent voting machine. The result generalizes and deepens the voting paradox to any voting rule satisfying the conditions, however comprehensive.

The 1963 edition includes an additional chapter with a simpler proof of Arrow's Theorem. It also elaborates on advantages of the conditions and cites studies of Riker and Dahl illustrating that as an empirical matter intransitivity of the voting mechanism may produce unsatisfactory decisions. These support Arrow's characterization of a constitution across possible votes as an important attribute of a "democratic system capable of full adaptation to varying environments."

The theorem might seem to have unravelled a skein of behavior-based social-ethical theory from Adam Smith and Bentham on. But Arrow himself expresses hope at the end of his Nobel prize lecture that others might take his result "as a challenge rather than as a discouraging barrier."

The large subsequent literature has included reformulation to extend, weaken, or replace the conditions and derive implications. In this respect Arrow's framework has been an instrument for generalizing voting theory and critically evaluating and broadening economic policy and social choice theory.

References

Kenneth J. Arrow, 1951, 2nd ed., 1963, Social Choice and Individual Values ISBN 0300013647
_____, 1983, Collected Papers of Kenneth J. Arrow, v. 1, Social Choice and Justice ISBN 0674137604
_____,” 1987, “Arrow’s Theorem," The New Palgrave: A Dictionary of Economics, v. 1, pp. 124-26
Amartya K. Sen, 1970 [1984], Collective Choice and Social Welfare, ch. 1-7.1 ISBN 0444851275

External links

[Acknowledgments]

[Table of Contents]

[Comments] of Frank Hahn, Donald Saari, and Nobelists James M. Buchanan and Douglass North

[Link to text] of Nobel prize lecture with Section 8 on the theory and background

[High-theory Economic Justice] with Arrow’s framework, context, and references in Sections 1 & 4

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