Using apostrophes with possessive nouns gets a little more confusing when the noun ends in a sibilant (an s, z or x sound). These nouns might end in one of those letters, or they might also end in se, ze, ce or xe.
Common nouns ending in an s, z or x sound should generally take an apostrophe and an s when indicating possession.
✅ The abacus’s beads.✅ Your boss’s husband.✅ The fez’s colour.✅ The US’s unemployment rate.✅ The box’s lid.
This is recommended by most style guides and authorities, including MLA, the BBC, The Economist and the OUP.
But many of these words sound and look awkward with the extra s, and in these cases — particularly when it would match pronunciation — it is encouraged to omit the extra s.
✅ Spelling is my Achilles’ heel.On that note, many authorities suggest that classical and biblical names ending in an s sound (particularly if they contain more than one syllable) shouldn’t take an s after the apostrophe.
✅ We can all learn something from Jesus' teachings.✅ Moses' early life is very interesting.
And if it’s just too awkward all-round, consider changing your possessive noun to an of, on, from, for to, in or another possessive or prepositional construction, or even transforming the possessive noun into an adjective.
✅ The beads on the abacus / the abacus beads.✅ The husband of your boss.✅ The colour of the fez.✅ The unemployment rate in the US / the US unemployment rate.✅ The lid for the box / the box lid.
There’s some contradictory advice out there about not using an s after the apostrophe for a word ending in an s sound — if the word that proceeds it also starts with s. So, the abacus’s significance should be the abacus’ significance.
