The Grammarphobia Blog

A buoyant principle

Q: I’m writing an article that includes a quote from Archimedes’ (or Archimedes’s) principle of buoyancy. Wikipedia, Britannica Online, and my Random House unabridged dictionary make “Archimedes” possessive by adding just an apostrophe, but proper grammar would require an apostrophe plus the letter s. Or am I missing something?

A: You’re right that a singular word, including a name, usually becomes possessive with the addition of an apostrophe and the letter s. My grammar book Woe Is I has this example: “The dress’s skirt, which resembled a tutu from one of Degas’s paintings, was ruined.”

But there are a couple of exceptions to this rule. When a classical or Biblical name ends in s, the general practice is to add only the apostrophe to make it possessive.

Here’s an example from Woe Is I: “Whose biceps were bigger, Hercules’ or Achilles’?” And Garner’s Modern American Usage has these examples: “Aristophanes’ plays,” “Jesus’ suffering,” “Moses’ discovery,” and “Xerxes’ writing.”

Also, we traditionally drop the s in a lot of “sake” phrases – “for goodness’ sake,” “for conscience’ sake,” “for righteousness’ sake,” etc. – to avoid adding another sibilant syllable to a pileup of hissing sounds.

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