In American English, attorneys general is the correct plural form. The British prefer attorney-generals (the Brits have long hyphenated the phrase).

Generally, a compound noun made up of a noun and a postpositive adjective (one that follows its noun) is pluralized by adding -s to the noun, as with heirs apparent and causes of action. But we add -s at the end of closed compounds, as with all words ending in -ful {spoonfuls, handfuls}.

And how do you make the plural phrase attorneys general into a possessive? You don’t, preferably. You might try to make a case for 35 attorneys general’s briefs, but you’d induce more head-scratching than readerly agreement. To avoid any miscues, the better course is to rephrase with an of-genitive. So if you want to discuss the briefs of more than one attorney general, simply say the briefs of the attorneys general. Fortunately, most jurisdictions have only one attorney general at a time, so the plural-possessive form is not a problem you’re likely to encounter often.

The British have it easier: 35 attorney-generals’ briefs. Tallyho!

Sources:

Garner’s Dictionary of Legal Usage 94, 685 (3d ed. 2009).

The Redbook: A Manual on Legal Style § 7.14, at 111 (2d ed. 2006).

Thanks to Daniel K. Crane-Hirsch and Roberta E. Nalbandian for suggesting this topic.

Bryan A. Garner, President of LawProse Inc., is the most prolific CLE presenter in the U.S., having trained more than 150,000 lawyers and judges. His book — most prominently Black’s Law Dictionary and Garner’s Modern American Usage — have been cited as authority by every state and federal appellate court, including the highest. For more about him, go to www.lawprose.org. To follow him on Twitter: @bryanagarner.