@flargh @gruber @MisterMoo The AP Stylebook rule is a result of a misinterpretation and should not be used. Apostrophes do not make a sound. They misinterpreted examples like “Jesus’” and “Moses’” as being pronounced “Jesuses” and “Moseses,” but of course they aren’t — “Jesus’ life” is pronounced “Jesus life,” not “Jesuses life.”

The creators of that rule did not understand this, and took it to mean that “Chris’ book” can be pronounced “Chrises book.” It cannot. Where would the second S sound come from when only one S is written? If you say “Chrises book,” which you undoubtedly do, you need to write “Chris’s book,” plain and simple.

Cases like “Griffiths” pattern like plural nouns, so the option “Griffiths’” is attractive, but they are still singular proper nouns, and for clarity “Griffiths’s” should be preferred, as should “Jobs’s” etc. Ultimately the same rule applies: any non-plural noun marks its possessive with “’s,” pronounced “es.”

The only exception (outside of the optional Biblical ones) is for words ending in a silent S: the singular noun “corps” ends in a silent S and its possessive form “corps’” just adds an apostrophe, which you can view as making the final S not silent leading to the pronunciation “cores.”