Can it really be true, as Stig Abel, new editor of the Times Literary Supplement, suggests in a tweet, that TLS‘s house style mandates -s’ if the person is of Jesus’ age or older, and -s’s for anyone younger: thus “Achilles’ shield”, or “Pythagoras’ bath” but “Charles Dickens’s novels” or “Hugo Lloris’s distribution problems”? It’s just too quaint.
Fowler’s Modern English Usage isn’t too helpful on the subject, telling us “it was formerly customary, when a word ended in -s, to write its possessive with an apostrophe but no additional s, e.g. Mars’ hill, Venus’ Bath, Achilles’ thews. In verse and in poetic and reverential contexts, this custom is retained, and the number of syllables is the same as in the subjective case, e.g. Achilles’ has three, not four; Jesus’ not Jesus’s. But elsewhere we now add the s.*” So is the TLS just being reverential to the ancients?
Typically Hart’s Rules doesn’t beat about the bush, though they do allow a certain room for judgement for euphony’s sake. “Jesus’ is an accepted liturgical archaism. In quotations from Scripture follow the Oxford settings. In ancient classical names uses s’ (not s’s): Mars’, Venus’, Herodotus’. This is the prevailing custom in classical works.” They also say “Use ‘s for the possessive case in English names and surnames whenever possible: i.e. in all monosyllables and disyllables, and in longer words accented on the penult . . . In longer names not accented on the penult, ‘s is also preferable though ‘ is here admissible” on the grounds of euphony. So in the end, rather tritely, we find that the TLS is actually only applying Oxford style!
* The sentence goes on to refer us to the case of “sake” where Fowler pontificates “when the enclosed word is both a common noun & one whose possessive is a syllable longer than its subjective, the s of the possessive is not used; an apostrophe is often, but not always written; for conscience sake, for goodness’ sake, for their office sake, for peace’ sake.” All very odd.