It is often thought that judicial unanimity is a valuable commodity. Chief Justices bang heads, twist arms, and break legs in order to get their courts to produce more of it, but they don’t always succeed, and unanimity remains at least somewhat scarce on the U.S. and Canadian Supreme Courts (although more on the former than on the latter, which has been unanimous in judgment in between two thirds and three quarters of its decisions rendered since 2010). The unusually high output of the unanimity production line at the US Supreme Court this year has produced much commentary. But how much do we really know about the economics of unanimity? What is it worth? More precisely, what is its purchasing power? How much does it cost? And is the cost worth what you get in return?
In the New York Times, Adam Liptak reviews some academic attempts to answer these questions (in the American context), including a recent paper by Cass Sunstein. The takeaway from this literature seems to be that unanimity is worth less than is commonly assumed. Mr. Liptak notes that people, including judges, often think that “[t]he public may be less likely to accept and follow decisions that would have gone the other way with the switch of a single vote.” Yet experiments ― and perhaps even historical experience ― do not bear out this intuition. And while another claim about the value of unanimity, that unanimous judgments are less likely to be reversed, is apparently supported by the facts, the number of overturned decisions is so small to begin with that this value is more illusory than real. Finally, although unanimous judgments might in theory make for a clearer legal landscape, they often fail to deliver on this promise too. Mr. Liptak points out that
Supreme Court opinions are the product of negotiation and compromise, which is why they can read as if written by a committee. A nine-member committee does not seem likely to produce crisper prose than a five-member one.
At the Volokh Conspiracy, Jonathan Adler chimes in, writing that
[t]he cost of broad agreement may be an opinion that speaks in generalities and pushes aside the potential points of disagreement. Concurrences and dissents often draw clearer lines and are more analytically coherent than majority opinions. The sorts of opinions that result from efforts to achieve greater unanimity are different from those that merely seek the median vote.
…
At the same time, coalescing around a narrow holding allows the Court to avoid premature resolution of a potentially divisive question, perhaps leaving it to be resolved when it can be resolved in a unanimous way or even putting it off indefinitely. This is itself a virtue of judicial minimalism, according to some.
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These are useful observations, so far as they go, but I think some additional clarifications are necessary for us better to assess the value (or lack thereof) of unanimity.
For one thing, we need to be clearer about what it is that we are talking about. Unanimity in judgment does not necessarily mean unanimity in reasoning, and indeed in some of the recent decisions of the U.S. Supreme Court (for example in NLRB v. Noel Canning, a case considering the constitutionality of President Obama’s “recess appointments”) unanimous judgment masks sharp disagreements about the law between a majority and a concurrence. In such cases, it seems unreasonable to expect the putative effects of unanimity, whether positive or negative, to manifest themselves.
For another, even unanimity in opinion can be of different sorts. While some unanimous decisions will indeed be the products of laboured compromise, and thus be likely to exhibit the flaws described by Mr. Liptak and prof. Adler, others are in fact the products of genuine agreement about the legal principles involved and their application. Probably most decisions of intermediate appellate courts (which have unanimity rates much higher than Supreme Courts, both in the U.S. and in Canada) are of this sort, because they are rendered in “easy” cases where the law is relatively clear. Some decisions of Supreme Courts, at least, are of this sort too. I don’t know American law well enough to give examples, but they are plenty this side of the border ― among the more notable recent cases, Reference re Securities Act, 2011 SCC 66, [2011] 3 SCR 837, comes to mind. Of course, it might not be easy for external observers to distinguish unanimity of agreement from the unanimity of compromise (and a single decision might involve both), but it seems likely that the former sort is more valuable, at least for clarifying the law (though not if one values unanimity for requiring narrow rulings!) ― but also less susceptible of deliberate manufacture by a court.
As for the value of unanimity as a means of exchange for acquiring legitimacy, I wonder whether an inquiry into the value “ordinary” people attach to it is the relevant one. The issue here does not concern unanimity alone. Rather, given well-documented and pervasive political ignorance, I wonder how much people outside the legal and political communities notice and care about judicial decisions at all, and to the extent that they do, how much their views of these decisions are influenced by what politicians (and perhaps experts) tell them. It is possible, and indeed likely, that the perceived legitimacy of the vast majority of, and perhaps of all, judicial decisions depends on the opinions of a certain class of journalists, lawyers, and politicians. If that is so, then an empirical assessment of the value of unanimity should look at the views of such people, and not of random citizens.
Finally, we might need a fuller picture of the transaction costs involved in achieving unanimity. Presumably, producing a decision that is unanimous in reasoning ― at least when unanimity of of compromise rather than of agreement is involved ― takes time and effort, which might, in theory, otherwise be expended on producing better decisions in other cases. It also, by definition, requires individual judges to sacrifice the opportunity to implement or even express their views about the law, and prevents disagreement from being aired in the open. It seems at least plausible that this will, for lack of a better term, undermine the morale of the court or at least of the more independent (or headstrong) judges. I don’t know, I’m afraid, whether this is a real problem (perhaps readers who have clerked at the Supreme Court can tell!). Judges surely know that they sometimes need to “take one for the team”, though nobody, I imagine, like to have to do that very often. In any case, the possibility is worth considering.
All that to say that, as with other commodities, unanimity doesn’t have any “true” value. How much it costs and what it can buy depends on a number of contextual factors. A quest, or demands, for unanimity that ignore these factors will likely be misguided, and perhaps pernicious.
Double Aspect 
My take on this is a little bit different. I think of courts, especially appeal courts, especially the highest appeal courts, as being in the “reduce legal uncertainty” business and making themselves and their decisions and the decisions they will make in the future as understandable and as predictable as possible. Lawyers, of course, are in the business of finding the remaining little pools of uncertainty, or even creating new little pools of uncertainty, so that they can try to exploit them to the benefit of their clients. The problem with divided courts — not just divided in the sense of having dissents that one day want to flip the whole thing in their favor, but more generally divided in the sense of having different sets of judges suggesting different takes on legal ideas and different legal trails to an optimal resolution, so including concurrences as well — is that they leave more questions open than usual. This is particularly important now that the “bite” of stare decisis is less emphatic than it used to be (or less emphatic than we describe it or think of it as having been), such that the “losing” judges do not reset their minds to coincide with the “winning” judges but rather persist in their disagreement, and dream of a future vindication that will not be the total turnaround of minority becoming majority, but will instead lead to a tweaking of the doctrine that brings it more in line with their minority position. Legal principles are far too complex and malleable to stake all our assessments on the relatively rare phenomenon of explicit reversal; looking for the cases where over time the minority reasons tend to be cited more often than the majority reasons is more fruitful. So the biggest effect of divided courts and small majorities is — more litigation, more attempts to exploit the larger pools of uncertainty that the disagreement has signalled and the several sets of reasons have fed.
Thanks, this is interesting! But I wonder what follows from your position. If judges agree with it (and they may well, for all we know), should they struggle to achieve a compromise decision? But such decisions risk being muddled themselves. Or should the judges in the minority simply keep quiet and sign on to the majority view (as judges in some European courts do, and as the members of the JCPC used to)? But if judges are capable of such self-abnegation, they might as well fall in line in future cases while retaining their prerogative of expressing dissent (or concurring for different reasons).