It's Christmas! Celebrate by not doing violence to the laws of pluralization. Photo illustration by Slate. Photo by DK-photo/iStock. Nothing quells my Christmas cheer as quickly as a stray apostrophe.

Pluralizing a last name can seem confusing—and it gets even more confusing when you want to make a name both plural and possessive. Let’s suppose your last name is Jones, and you and your family want ...