Majority rule

Majority rule is a procedure for deciding among alternatives by counting votes, but it is not, by itself, a guarantee of wisdom or justice. In the book’s account, collective judgment depends on the conditions that shape a group’s decisions, while democracy has a significance beyond producing the most accurate answer: it gives people a way to coordinate, cooperate, and accept outcomes they did not choose.

Majority Judgment and Collective Intelligence

The book’s account of wise crowds identifies four conditions that help collective judgments succeed: diversity of opinion, independence of judgment, decentralization, and aggregation. Majority rule is one possible way to aggregate individual choices, but the procedure cannot supply the information or independence that the participants’ judgments lack. When people’s views are diverse and independent, aggregation can offset individual errors; when those conditions fail, a count of votes may simply reproduce shared mistakes.

Evidence from other collective judgments illustrates both the possibilities and limits of aggregation. In NFL betting, favorites cover the point spread in about half of games and underdogs in the other half, while the Mirage’s final line is described as the most reliable available forecast about three-quarters of the time. The Iowa Electronic Markets, meanwhile, averaged errors of 1.37 percent in presidential elections, 3.43 percent in other U.S. elections, and 2.12 percent in foreign elections across forty-nine elections from 1988 to 2000. These are examples of markets combining judgments, not demonstrations that a majority vote will always be accurate: the mechanism and incentives differ, and accuracy depends on information reaching the collective decision.

Diversity, Information, and the Limits of Counting

Experiments discussed in the book emphasize that the composition of a group can matter as much as the ability of its individual members. In computer simulations by political scientist Scott Page, groups of ten or twenty agents with varied skills often outperformed groups composed only of highly capable agents. Randomly selecting a group and letting it work could do as well as, or better than, carefully identifying the strongest agents and putting them together. The result supports a specific claim: cognitive diversity can improve problem-solving, while intelligence alone does not ensure that a group has a sufficiently wide range of perspectives.

The same distinction applies to institutional decisions. Decentralization lets people specialize and draw on local or tacit knowledge, but it does not ensure that information discovered in one part of a system reaches the rest. Before September 11, the U.S. intelligence community had specialized agencies but lacked an effective mechanism for aggregating judgments across them. The book contrasts aggregation with simply placing a central authority over all information: linking databases and sharing information could improve collective use of knowledge without discarding the benefits of specialization and autonomy. A voting rule, like any other aggregation mechanism, can only work with the judgments and information that reach it.

Democratic Procedure and Public Purpose

The book distinguishes the question of how democracy makes decisions from the question of what democracy is for. Critics of deliberative democracy doubt that citizens have the time or inclination to develop informed views about the common good. The disagreement, as framed in the book, concerns whether democracy should be valued for giving people a sense of control and supporting political stability, for protecting self-rule even when citizens make unwise choices, or for producing intelligent decisions and uncovering truth. Majority rule bears on how a decision is reached, but these competing accounts concern the purpose and legitimacy of the procedure as well.

The book’s concluding argument places democracy chiefly in the domain of coordination and cooperation, rather than treating it as a reliable machine for discovering a single public interest. Collective arrangements such as norms of fairness emerge over time and can be fragile, yet they may work without being imposed from above. Democracy similarly makes people experience not getting everything they want: opponents sometimes prevail, and citizens accept that result in part because they expect their valued institutions to endure and another opportunity to pursue their aims. In this account, the democratic decision need not demonstrate the wisdom of the crowd; the choice to decide democratically is itself significant because it sustains compromise and the possibility of shared life.