Readers seemed to enjoy “Are Two r’s One Too Many?” our column about the pronunciation of February. But we also received a few emails like this one: “Why on earth is there an apostrophe in the title??”

We understand the reader’s concern. Starting in grade school, English teachers rail against sentences like “Banana’s make good snack’s.” Students learn early on that only careless or clueless writers use apostrophes to pluralize nouns.

However, there are certain exceptions. When a rule leads to perplexity rather than clarity, writers and editors will make adjustments. For instance, the use of apostrophes strikes us as the simplest and most practical way to pluralize is and was in a sentence like Jones uses too many is’s and was’s. You may feel you have a better solution, but the is’s and was’s solution is not wrong. It is endorsed by many reputable language authorities.

These days, initialisms like TV or RSVP are made plural simply by adding a lowercase s without an apostrophe: TVs, RSVPs. But to pluralize abbreviations that end in S, we advise using an apostrophe: They sent out two SOS’s.

Imagine the confusion if you wrote My a’s look like u’s without apostrophes. Readers would see as and us, and feel lost.

This brings us back to our title and the phrase “two r’s.” The Chicago Manual of Style (CMOS) endorses “Mind your p’s and q’s.” The Practical English Handbook by Floyd C. Watkins, William B. Dillingham, et al., sanctions “four c’s,” but the book also accepts “four cs,” presumably because the difference between c in italics and s in roman typeface is sufficient for attentive readers.

There is no definitive rule for using apostrophes (or not) to form plurals in special cases like these. For many decades The New York Times wrote the 1920’s. Then the paper changed its policy in late 2012, and now writes the 1920s like most of the rest of us. And though CMOS recommends “p’s and q’s,” it prefers yeses and nos to yes’s and no’s. One wonders if CMOS would prefer ises and wases to is’s and was’s—because to us, ises and wases is too obscure to be a practical solution.

So to avoid similar confusion, we went with “Two r’s” and not “Two rs” in our title. We didn’t feel comfortable signing off on something that looked like a typo.