Q. My boyfriend and I are having a battle royal over the use of apostrophes in plural names. In his PhD dissertation he repeatedly refers to a family by the name of Wallace. When he refers to them in the plural, he insists that the correct form is “the Wallace’s,” which seems entirely incorrect to me. I hold that it should be “the Wallaces,” just like “the McDonalds” or “the McPartlands” or “the DeVitos.” He is backing up his position with the example “the G.I.s,” which he insists should be pluralized as “the G.I.’s.” Please help. This is ruining our dinner conversation!

A. Usually in such arguments, the woman is right. Yours is no exception. The plural of names of persons and other capitalized nouns is usually formed with the addition of s or es. An apostrophe is never used to form the plural of family names. Write “the Wallaces,” “the Joneses,” the “Jordans,” etc. See paragraph 7.9 of the seventeenth edition of CMOS for the full statement of the applicable rule. As for G.I., Chicago style is GI (no periods), the plural of which we write as GIs. See paragraphs 10.4 and 7.15.

[reply from Q.]: Ohhhh thanks!!!! I can’t wait to show this to [my boyfriend].