In the era of a polarized and stymied Congress, in which legislation is especially prone to be paralyzed by the filibuster and other supermajority devices, Melissa Schwartzberg’s new study of supermajority rules could not be more timely. In another sense, it could not be less timely: Schwartzberg generates her insights by recovering the origins of voting, majority rule, and supermajority rule in pre-modern polities. Her findings suggest that supermajority rule ought to be suspect in a polity otherwise committed to democratic principles of equal political dignity among voters.

To understand why this book is so innovative and so excellent, one needs to start elsewhere, with a peripatetic Scottish economist named Duncan Black. Active from the late 1940s through the 1970s, Black had no fixed academic post, but roamed the American academic scene in a series of visiting positions. This was a failure of the academic market to identify and reward genius. In a series of papers written around 1948 and in a book a decade later, Black laid the foundations of a branch of economics, or perhaps of political economy, known as social choice theory. Schwartzberg’s book is both a contribution to social choice theory and a corrective for its most conspicuous ills.

In its broadest sense, social choice theory is the study of collective decision-making. Given a group, and some need for a collective decision, how should the group decide what to do? In this sense, social choice has been firmly on the agenda of political theory at least since Aristotle. Black’s innovative approach was to mathematize and formalize social choice theory, both sharpening and narrowing its point. In the new world of mathematical social sciences in the postwar era, Black rediscovered the work of earlier scholars who had dabbled in formal social choice theory, such as the French polymath Condorcet and the English logician Charles Dodgson (“Lewis Carroll”). Yet it was Black’s work, and the roughly simultaneous work of Kenneth Arrow, that ignited an explosion, further fueled by major contributions from Amartya Sen and others in the 1960s and 1970s.

Collective decision-making is a living subject.

Social choice quickly became an enormous subfield of political economy, especially notorious for its pessimistic results and its skepticism about the possibility that democratic polities could aggregate preferences in a manner that would be both fair and coherent. Graduate students, later professors, would spin out nth-decimal mathematical refinements on Arrow’s Impossibility Theorem, which (very roughly) showed that under certain conditions collective choice rules could not be both democratic and coherent or stable; Sen’s proof of the impossibility of a Paretian Liberal, which (very roughly) showed that under certain conditions one could not be both a political liberal and a believer in the ultimate value of individual welfare, as determined by the free choices of the individuals themselves; and theorems showing that collective decision rules could not be strategy-proof—in other words, could not bar manipulation by voters willing to misrepresent their preferences. Libertarian political economists, such as William Riker, attempted to use these results to ground a sort of generalized suspicion of legislatures and other democratic institutions, which they argued were incapable of acting both coherently and democratically. Riker thus argued for a minimalist form of libertarian democracy, featuring a robust role for constitutional protections enforced by the judiciary. That attempt deflated, however, when it was pointed out that the main incoherence results of social choice theory applied just as strongly to collective voting on multi-member courts as to democratically elected bodies.

In a pattern seen wherever the social sciences become formalized, the mathematics of social choice eventually became an end in itself. Social choice theory became ever more recondite and inaccessible to the non-mathematical sectors of the university; the result was a kind of self-ghettoization, as social choice was segregated from fruitful contact with other disciplines. More seriously still, social choice cut itself off not merely from the university but also from the world. The inputs from reality, from the novel and ever-changing forms of collective decision-making used in the world’s institutions, all but dried up. The consequence was that, although social choice theorists were admired for their high IQs, signaled by their ability to manipulate theorems, the enterprise as a whole degenerated, producing a stream of essentially meaningless minor refinements. According to Jon Elster, the journal Econometrica even imposed a moratorium on social choice articles, on the ground of their patent irrelevance to real politics.