A typical non-majority opinion is written by a Supreme Court justice and joined by other justices — the author’s identity is clearly set forth. Both the author and those who join fully endorse the opinion (unless some of the justices join only parts of it), but it’s clear who the author is. Thus, in Hobby Lobby, we see “Justice Ginsburg, with whom Justice Sotomayor joins, and with whom Justice Breyer and Justice Kagan joined as to all but Part III-C-1, dissenting.” This is largely also true of majority opinions, which are labeled as the “opinion of the Court” but with the single authoring justice specifically identified (“Justice Alito delivered the opinion of the Court”), though some such opinions are labeled “Per curiam,” and thus don’t reveal their authorship.
But the short Breyer/Kagan separate opinion isn’t Justice Breyer, joined by Justice Kagan, or vice versa; it’s labeled,
Justice Breyer and Justice Kagan, dissenting.
And the text of the opinion fits with the introductory line: It uses “we” (“[w]e need not and do not decide”) rather than the “I” (e.g., “Undertaking the inquiry that the Court forgoes, I would conclude that …”) used in Justice Ginsburg’s opinion. This isn’t unprecedented; the NFIB v. Sebelius dissent was labeled an opinion of Justices Scalia, Kennedy, Thomas, and Alito, and the famous O’Connor/Kennedy/Souter opinion in Planned Parenthood v. Casey was labeled an opinion of all three justices. (“Justice O’Connor, Justice Kennedy, and Justice Souter announced the judgment of the Court and delivered the opinion of the Court.”) And I doubt that it’s particularly telling about anything substantive. Still, it was unusual enough that I thought it was worth a brief mention for the benefit of serious court-watchers.