Rules of Punctuation ( The Apostrophe)

 The Apostrophe

(a) To denote possession with nouns. The singular noun takes an apostrophe followed by an s. Plurals ending in s add an apostrophe after the final s.

e.g. a lady's hat, the ladies' hats (i.e., the hats of the ladies), a weeks holiday, six weeks' holiday. An ass's burden Jones's cap, the Joneses' house (i.e., the house of the Joneses)

Be careful with unusual plurals (like men, children, mice) which are treated as if they are singular:

e.g. men's coats, women's rights, children's toys (never write mens' or childrens')

For proper nouns ending in a sounded e and and an s or in s vowel s (e.g, Euripides, Moses) add the apostrophe after the s:

e.g. Ulysses' adventures, Archimedes' principle, Jesus' mother (Note-also-for goodness' sake.)

In units involving two or more nouns or in a compound noun or phrase, put the apostrophe on the last word only:

e.g. William and Mary's reign, my father-in-law's house.

This does not apply if there is no joint possession:

e.g. My brother's and my sister's birthday.

Note: The apostrophe is not used in these words: yours, hers, ours, theirs or its (when it means belonging to it). (Would you write hi's for his?) It is, however, used in one's (belonging to one).

(b) To indicate a contraction. The apostrophe is placed where the letter (s) have been omitted:

e.g. didn't, can't, they're, you're, I'd (But note: shan't, won't).

(c) For the plural form of certain letters and figures, although this apostrophe is now often omitted:

e.g. The three R's, P's and Q's, in the '60's, if's and but's.