What’s the rule on forming a singular possessive of a name ending with a sibilant? The answer has always depended on whom you ask.

The Harris campaign has used both Harris’s and Harris’, but their view can’t be seen as authoritative. Nor does it matter that Michael Dukakis opines that it should be Harris’. He apparently dislikes Dukakis’s.

It’s really a question of “house style” — and whether you’re a member of the Chicago Manual camp (Harris’s) or the AP Stylebook camp (Harris’).

And then there’s the question of which camp has the better position.

The issue would have lain dormant if Harris hadn’t picked Walz as her running mate, thereby highlighting an anomaly in the AP system, which specifies this: Do you prefer Harris’ speaking style, or Walz’s? What? Harris’ but Walz’s? Really?

People who yearn for consistency — who like sensible, nondistracting orthography — are understandably bothered by Harris’ alongside Walz’s. Let’s have some history, which has been notably lacking so far in the journalistic treatments of the issue.

Like so many other literary standards in English, apostrophe use came to be regularized in the 17th and 18th centuries. To illustrate: In Shakespeare’s First Folio (1623), only 4 percent of singular possessives (or genitives) were marked with ’s. Instead, the possessives looked like plural nouns, without an apostrophe. By the time of the Fourth Folio (1685), the printers had supplied apostrophes pretty consistently for singular possessives. The standard for the singular possessive ’s was ensconced: The apostrophe was thought to represent an elision of either the Old English genitive e (Johnes book) or the first two letters of his (John his book). It hardly matters today, but English-language historians can’t quite agree on what was being elided. We do know, though, that ’s was soon normalized for all singular possessive nouns and proper nouns (not pronouns!).

But there were some literary exceptions: for conscience’ sake and for goodness’ sake — where the apostrophe alone represented the singular possessive. Some grammarians stated this exception as belonging exclusively to the word sake, others as belonging exclusively to words ending in ce. Imagine referring to “J. D. Vance’ speech.”

It may have been George Glyn Scraggs who, in his book English Composition (1802), first expressed the idea that ’s might lead to excessive sibilance, or (in his words) “hissing sounds.” Hence the rule had exceptions. That’s probably the gist of what you learned in school: a rule with exceptions. But what exceptions, precisely, did you learn? How circumscribed were they?

That’s worth delving into, because the literature on English composition displays a bewildering variety of exceptions, even to this day. Imagine yourself as a grade-school teacher inculcating into your pupils the method for forming singular possessives. Your students might readily understand an exceptionless rule specifying ’s in all circumstances (a child’s book, a building’s foundation, James’s home, Sophocles’s plays, Judas’s perfidy). But that’s not what’s generally taught.

So what are the exceptions? If we take just post-1900 texts (I consulted more than a hundred), we find 15 different exceptions to the rule that you add ’s to form the singular possessive. Each of these variants is supposed to be the sole exception to the rule:

(1) The ’s produces a repetitious hissing sound that is “displeasing to the ear” — a supposed “genitival cacophony” (as with Demosthenes’s susurrations);

(2) you’re composing poetry;

(3) the resulting form is difficult to pronounce (Demosthenes’s orations);

(4) the word or name ends in s, ss, ce, or x;

(5) the phrase is one of a handful of idioms using sake: righteousness’ sake, conscience’ sake, goodness’ sake;

(6) the name is an ancient proper name ending in es: Ceres’ rites, Aristides’ exile, etc.;

(7) the name is either ancient or biblical (Achilles’ heel, Icarus’ wings, Moses’ law);

(8) the name has at least two syllables and ends in s;

(9) you wouldn’t pronounce the word as if it had a new syllable because of the possessive (“say the word aloud, both with and without the additional s, and then decide which is preferable”);

(10) the name ends in s or z (Agassiz’ headquarters);

(11) the last syllable of the name is pronounced /iz/ (Bridges’, Moses’, but James’s, Thomas’s);

(12) the last syllable of the name has more than one sibilant (Jesus’ followers);

(13) “the word ends in two sibilant sounds (ch, j, s, sh, or z) separated only by a vowel sound” (presumably Gorsuch’ book?);

(14) a noun ending in s is “followed immediately by a noun beginning with s, or else the noun ends in ses, or sses or ssess, or in sis or siss or ssis, or in xes”;

(15) a polysyllabic name has a last syllable that (a) begins and ends with an s or s sound and (b) is unaccented.

I’m not making this up. And believe it or not, all those versions can be found in textbooks. Good luck sorting it out. Which exception would you be willing to teach?

The AP Stylebook decided in 1953 to “simplify” by specifying that the apostrophe alone — without the extra s — should be used for words and names ending in s. (The s is essentially treated as if it were a plural.) Gradually, this position became a cherished tenet of most newspaper journalists. For many, it’s akin to an unshakable religious belief — so much so that its adherents see no problem with Harris’ alongside Walz’s.

Meanwhile, the Chicago Manual decided in 2010 to “simplify” by stating a rule without exceptions: Add ’s to form all names as singular possessives — even possessives for ancient names (Demosthenes’s).

We haven’t even touched on plural possessives, where all the authorities agree but there is widespread confusion within the general population. The correct forms are the Harrises’ house, the Walzes’ investments, the Vances’ travels. Doubtless the Harrises, the Walzes, and the Vances agree on this much. Copy editors certainly do.

Which brings us back to the Harris campaign and how best to attract the votes of America’s copy editors — all 250 of them. My recommendation would be to make no official statement about the campaign’s preference for Harris’s or Harris’. Stay silent until after the election. Otherwise, the campaign risks alienating either the Chicago camp or the AP camp.

But if they must choose, I’d urge the Chicago preference, which is also NR’s preference: Harris’s. And by the way, this month the newly revised, 18th edition of The Chicago Manual of Style is being released. As a contributing author to that tome — I wrote chapter 5, “Grammar and Usage” — I heartily recommend that you acquire several copies. There’s hardly a better gift for a college student, or even a talented high-schooler. Who cares today if it might not get Dukakis’s endorsement?