I think Elena Kagan will be an outstanding Justice, not just because of her outstanding (and underrated) technical abilities—as I'll mention shortly, I think the Court as a group is already well-stocked, if anything overstocked, with technical legal skills—but because she possesses that rarest of qualities, the charisma of leadership. This is now a Court with two natural leaders—Kagan and Roberts—and the fascinating question will be whether the building is large enough to contain two outsize talents of the same type.
Stepping back from Kagan, I'm struck by the narrow bandwith of the debate over her qualifications. The political system has converged to a point at which all the Justices attended either Harvard or Yale, and the only question is whether all nine of the Justices should be former lower-court federal judges—in effect that was the Republican position —or whether it's acceptable to have one Justice who, like Kagan, has never served as a judge. Those positions are shockingly narrow, on at least three dimensions. First, not all good lawyers attended either Harvard or Yale, heretical though that claim might seem; the opposition to Harriet Meiers was pervaded by the snobbery of the elite bar, who sneered at her credentials. Second, many great Justices had no previous service as federal appellate judges; given that the Court decides many cases that involve high politics, one might think that having at least a few Justices who served in elected office or in the upper reaches of the executive branch might usefully diversify the Court's base of experience and information. Third, and most radically, I believe there is a good case that the Court should contain at least a few non-lawyers. Let me expand on that last point, which is outside the mainstream, but which is supported by a growing body of academic work on the determinants of good collective decision making.
No legal rule requires that appointees to the Court be lawyers, in the sense of possessing a J.D. degree and being a member of a state bar association. The Court's docket, roughly speaking, consists of two types of cases—"autarkic" cases in which the legal issues are strictly technical and internal to law, and "non-autarkic" cases in which the right legal answer itself depends upon the answer to questions about which lawyers have no specialized technical ability or comparative advantage. Examples in the latter category include the questions about the effect of climate change debated in Massachusetts v. EPA, a case from a few years ago, or the questions about the nature and consequences of military detention that the Court has debated in several cases after 9/11. In the non-autarkic cases, a group consisting solely of lawyers is likely to be at sea; a group containing at least one member with relevant non-legal expertise is likely to make better decisions. The illusion that drives the debates over qualifications for Justices is that the Court does only technical lawyers' work. Although that is more often true for lower federal appellate courts, a great deal of the Court's docket involves questions of fact, causation or policy in various specialized nonlegal fields or else involves matters of high politics, as to which legal training is essentially irrelevant. Ironically, then, the insistence that all or nearly all Justices should have been lower federal judges selects for technical legal skills, precisely the dimension on which the work of the Court differs from the work of the lower federal courts.
The larger point is that a growing body of research and theory shows that cognitively diverse groups make better decisions. The main benefit of cognitive diversity is that it reduces the degree to which members of the group have correlated biases, and thus tend to make the same sorts of mistakes. The economist Krishna Ladha showed in the early 1990s that groups with lower correlation of biases might actually reach correct answers more often than groups with a higher level of technical competence but greater correlation of bias. More recently the political scientist Scott Page has expanded on this idea, detailing many situations in which cognitive diversity helps group decision making. The nub of the insight is that in the more cognitively diverse groups, errors in various directions tend to cancel out, and the right answer tends to prevail. The less diverse groups, by contrast, tend to err badly as to matters in which their biases all point in the same direction. Diversity of training and profession is correlated with cognitive diversity; conversely, professional homogeneity creates likemindedness.
The problem with a Court composed of all lawyers is that, by virtue of training or self-selection into the legal profession, lawyers' biases are highly correlated, and the group will tend to have corporate blind spots. I don't deny that most of the Justices should be lawyers; I suggest only that the legal system might do better with a group of Justices that contains at least one non-lawyer than with a group of lawyers alone. To be clear, this argument is not at all a populist one, based on the idea that adding non-lawyers would make the Court more "democratic" or something of that sort. It is a strictly technocratic argument; but the point is that a professionally diverse group will make better technocratic decisions, even in the legal cases that reach the Court.
Even if one thinks that appointing non-lawyers to the Court is too radical, at a minimum, one might diversify the Court's informational base by appointing Justices who possess some form of dual competence—legal training plus credible expertise in some other discipline or subject matter. Suppose we accept that appointees must be lawyers who have served as judges. Why not look outside the ranks of the generalized federal judiciary, and instead consider appointees who have served on one of the many more specialized federal tribunals—the Tax Court, the many administrative courts, the Federal Circuit (which handles patents, other intellectual property matters, and certain money claims against the government), or the system of military courts? Even within the class of generalist federal judges, what about appointing a Justice who has dual competence—perhaps someone with a second degree in finance, accounting, economics, medicine, environmental sciences, or engineering, or a former military lawyer? The political incentives to nominate candidates only from a pool defined in the narrowest of terms are powerful, intelligible, and damaging.