Milana Vinn, a first-semester student from Russia, e-mailed to ask: “What is the correct grammar for this sentence? Syria is one of the countries that are in a war zone.”

“That is absolutely CORRECT!” I wrote back, and thank you for asking.

In subject/verb agreement (for a quick review, click here), one of the trickiest cases is sentences like these. Even many native English-speakers would say the verb in that sentence should be are, since cases, plural, immediately precedes it. But they’d be wrong. The subject is one, modified by the prepositional phrase of the trickiest cases, so the verb needs to be singular.

Milana’s example is different.”I was unsure because many of my classmates were convincing me Syria is one of instead of Syria are!” she explained later. To dissect the entire sentence:

One of the countries that are in a war zone is a predicate nominative equal to Syria. Syria is indeed one country, at least for the moment, but in this sentence it is one of multiple countries under discussion. What kind of countries? Those that are in a war zone. That relative/dependent/subordinate clause, functioning as an adjective, modifies countries, not one, so the verb needs to be plural.

In some cases, though, the verb could be either singular or plural, depending on the intended meaning. From The New Yorker:

One of the studio’s programmers who was with Murray backstage recalls. . .

Speaking of one of, one of the things that drive* me crazy in student writing, or anyone’s, is** the phrase one of the only. Last year a Danish student wrote:

The Danish People Party wants to reinforce the border control and they are one of the only parties who focus on the lockdown of the Western part of Denmark.

Other singular/plural problems aside (in American English, a collective noun like political party is considered singular, hence it rather than they), that phrase is all but meaningless. If the party is focusing on the lockdown, obviously it’s one of the “only” ones doing so, no matter how many there are. The writer meant one of the few.

So did Nick Bilton, whose article in the October Vanity Fair on the collapse of the Theranos blood-testing company includes this sentence:

One of the only journalists who seemed unimpressed by this narrative was John Carreyrou, a recalcitrant health-care reporter from The Wall Street Journal.

Carreyrou was one of the few journalists.

But it’s fine to say one of the only if it’s followed by a number, as in this sentence from a Chinese student, now alumna, a few years ago:

Chen was one of the only three people who responded.

* Because its subject is things, plural.

** Because its subject is one.