Form the possessive singular of nouns by adding 's.

Using the short form of my first name, I've got two names ending in "s." Sure, it took me a little bit of time as a kid to come to grips with Strunk and White's Rule 1, but it's been worth it if only to enjoy the entertainment provided by seeing the rest of the world struggle with counterintuitive punctuation.

Two weeks ago we went to visit my uncle. Some years ago someone gave him as a gift one of those etched "Welcome to my house" stones. I can just imagine the stone etcher contemplating not taking the order. Do you really say that two people named Lucas are Lucases? Where does the apostrophe go? Are you sure?

I don't know whether the etcher was informed that my uncle is a bachelor, and whether this knowledge would have made the job any better or worse. I only know that the finished stone identifies the house as The Lucas s. No plural. No apostrophe. Just a tiny space.

This is the weirdest imaginable result. It's actually a source of inspiration to me, as I've recently undertaken a regimen of exercises to firm and tone the Lucass.