In most cases, a supreme court opinion has one justice listed author, though one or more other justices may join. However, in the recent case Dobbs v Jackson Women's Health Organization, the single dissenting opinion is attributed to three justices. How common is it for a supreme court opinion to have multiple listed authors, and what reasons might there be for this?
Usually a Supreme Court opnion has a single author, although often multiple Justices "sign" or "join" the opinion, meaning that those Justices agree with both the reasoning and the result. It is very common for ma Justice who is not the author to suggest specific wording for an opnion, anywhere from a single word to several paragrahs or even pages of writing. Such suggestions are not usually formally credited. However, in some cases an opinion is drafted by a committee of justices, with each taking one or more sections of the opinion. This may be done to speed up the drafting, or to make sure that the opinion will be acceptable to a wider ranger of the Justices, or for other reasons.
The book The Brethren by Woodward and Armstrong describes several occasions when the Burger court used committee opinions, usually drafted by three Justices.
An opinion signed by the entire court, rather than by any single author, is called a per curiam opinion (that is, “by the court.”)
These are usually very short and have minimal explanation. A typical example reads, in its entirety,
The judgment is vacated, and the case is remanded to the United States Court of Appeals for the District of Columbia Circuit for further consideration in light of Johnson v. Jones, ante, p. 304.
Apparently, the justices took two cases in the same term that were essentially the same, decided one, and then unanimously said about the other, “Same as the last one.” Both decisions were unanimous, but only the first one got a signed, lengthy opinion.
But one famous example that was not like that at all was the U.S. Supreme Court’s opinion in New York Times Company v. United States, the “Pentagon Papers case.” The only majority opinion was a short per curiam opinion that merely said that the New York Times had won, and did not even try to explain why they won. The Supreme Court does not actually have to give any reasons for its decisions, and none of the justices could agree.
In “realist” terms, what happened was that there were six votes in favor of the New York Times, but those six justices had enough disagreements that they refused to sign on to any other justice’s opinion and let it become a legal precedent. So they compromised on a holding that set no precedent, and they all got to attach their own individual opinions where they separately said what they really thought. Usually, when something like this happens, one of the justices writes an opinion with multiple parts, and the others who agree with the holding for a different reason say they concur “in part” Here, they could not even agree to do that.