Some writers will say that the -s after Charles' is not necessary and that adding only the apostrophe (Charles' car) will suffice to show possession. Consistenc

Some writers will say that the -s after Charles' is not necessary and that adding only the apostrophe (Charles' car) will suffice to show possession. Consistency is the key here: if you choose not to add the -s after a noun that already ends in s, do so consistently throughout your text. William Strunk's Elements of Style recommends adding the 's. (In fact, oddly enough, it's Rule Number One in Strunk's "Elementary Rules of Usage.") You will find that some nouns, especially proper nouns, especially when there are other -s and -z sounds involved, turn into clumsy beasts when you add another s: "That's old Mrs. Chambers's estate." In that case, you're better off with "Mrs. Chambers' estate."