Making the last name of the family in my novel, The Tedescos, plural was quite easy. I simply added an S to their name when speaking or writing about the entire clan. And then I assigned one character the last name Roberts and decided to write about his family as well. Time to apply “The Joneses Rule.”
Of course this isn’t the official title of the grammar rule; it’s just my way of remembering that when I make a last name ending in S plural, I add –es. The AP Stylebook, The Chicago Manual of Style, the Cambridge Guide to English Usage, Garner’s Modern American Usage as well as many grammar websites agree with this practice.
Then there is the annoying little pronunciation rule that pops up every now and then. If a last name ending in S sounds like a Z, as in Jones, one shouldn’t add the –es. A trick to determining this is to place your hand on your throat, say the name aloud, and see if you can feel your throat buzzing. Really? We’re supposed to trust proper grammar to the buzzing in our throats? This is made doubly ridiculous because sites that uphold this rule still say that Jones should be Joneses when making the name plural.
Here’s my advice: play it safe by trashing the buzzing rule, be consistent in your writing, and add –es to any last name ending in S. Regional dialects pronounce names differently, and it’s too difficult to pin down whether a name is ending in an S sound or a Z sound.