<i>Some writers will say that the -s after Charles&#x27; is not necessary and that adding only the apostrophe (Charles&#x27; 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&#x27;s Elements of Style recommends adding the &#x27;s. (In fact, oddly enough, it&#x27;s Rule Number One in Strunk&#x27;s &quot;Elementary Rules of Usage.&quot;) 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: &quot;That&#x27;s old Mrs. Chambers&#x27;s estate.&quot; In that case, you&#x27;re better off with &quot;Mrs. Chambers&#x27; estate.&quot;</i>