I’ve taken the following information directly from the
“Editorial Inspirations Newsletter,” by April Michelle Davis.

EiHeader_New

Most writers know that an apostrophe shows possession for a noun; the omission of some letters in a word or numbers in a year; and the plurality of single letters, numbers, and abbreviations. But the apostrophe has other uses as well that may not be in the forefront of our minds when we are writing. Refresh your knowledge of the apostrophe by reviewing its other uses below.

Double possessive (double genitive): use of and apostrophe s in the same phrase

a friend of Mary’s

Joint possessive: use an apostrophe on the last item in a series when the subjects own an item together

Frank and Sue’s house (they share one house)

Bob, Tim, and Fred’s sister-in-law (they have the same sister-in-law)

Possessives of possessive names: do not use another apostrophe s if the name of a company or thing is already possessive; recast the sentence or use the original possessive name again

Mary and Mariah love going to Friendly’s. The fries at Friendly’s are the best, they say.

Possessives of inanimate objects: use an apostrophe when the object is singular

The car’s engine is overheating.

The laptop’s hard drive is broken.

Set phrases: use apostrophe s in an idiomatic way for a couple of set phrases

mother-in-law’s car

anyone else’s book

Units of measurement: use an apostrophe when the unit modifies a noun

15 years’ experience

two weeks’ notice

4 yards’ worth of fabric

The omission apostrophe: use an apostrophe when making contractions

don’t

wouldn’t

po’ boy

The plurals apostrophe: use an apostrophe when making single letters, numbers, and abbreviations plural

Robert got all A’s on his report card.

Disco was popular in the 1970’s.

The CEO’s are meeting after the VP’s.

Note that whether or not an apostrophe is used to form plurals depends on the style guide you are following. The above examples follow the rules of the New York Times. For example, the Chicago Manual of Style, 16th edition, recommends the following:

Robert got all As on his report card.

Disco was popular in the 1970s.

The CEOs are meeting after the VPs.

Try It!

Determine which word in italics is correct using the New York Times and/or the Chicago Manual of Style style guides.

1. A friend of Beth’s/Beth came with us to the movies.

2. John and Sally’s/John’s and Sally’s house has three bedrooms.

3. Susan and John like T.G.I. Friday’s’s fries. / Susan and John like the fries at T.G.I. Friday’s.

4. The book/book’s pages are crumpled.

5. My brother’s-in-law/brother-in-law’s truck is red.

6. I decided to give my two weeks notice/two weeks’ notice today.

7. I wont/won’t go to bed until I brush my teeth.

8. Rebecca got all B’s/Bs in her English class.

9. The Beatles were very popular in the 1960s/1960’s.

10. The VPs/VP’s are meeting after lunch.

Answers:

1. Beth’s; 2. John and Sally’s; 3. T.G.I. Friday’s; 4. book’s; 5. brother-in-law’s; 6. two weeks’ notice; 7. won’t; 8. B’s (NYT), Bs (CMS); 9. 1960’s (NYT), 1960s (CMS); 10. VP’s (NYT), VPs (CMS)

Depending on your grasp of grammar, this is either an excellent lesson or handy refresher. Many thanks to the author for her expertise!