AMA Manual of Style - Stacy L. Christiansen, Cheryl Iverson 2020

Apostrophe
Punctuation

8.7.1 To Show Possession.

Use the apostrophe to show the possessive case of proper nouns in accordance with the following examples (see 15.2, Eponyms, Nonpossessive Form):

Jones’ bones (1 person named Jones)

the Joneses’ bones (2 or more people named Jones)

If a singular or plural word does not end in s, add ’s to form the possessive.

If a proper noun or name ends in a silent s, z, or x, form the possessive by adding ’s.

Theroux’s The Mosquito Coast

Degas’s work

If a noun ends in a nonsilent s, form the possessive by adding an apostrophe:

The scissors’ point had been dulled over the years.

8.7.2 Possessive Pronouns.

Do not use ’s with possessive pronouns: his, hers, ours, its, yours, theirs, whose.

The idea was hers.

Give the book its due.

Do not confuse the contraction of it is (it’s) with the possessive its, eg, “It’s an excellent resource. I have not seen its equal.”

8.7.3 Possessive of Compound Terms.

Use ’s after only the last word of a compound term.

8.7.4 Joint Possession.

When joint possession is being shown with an organization’s or business firm’s name, use the possessive form only in the last word of the noun or name.

US Food and Drug Administration’s policy

Farrar, Straus and Giroux’s books

Centers for Disease Control and Prevention’s Task Force

Hammond and Horn’s study

When possession is individual, each noun takes the possessive form.

We matched the infant’s and mother’s records.

Note: When one of the nouns takes a possessive pronoun, the other nouns take the possessive as well.

I presented the intern’s and my workups.

8.7.5 Using Apostrophes to Form Plurals.

Do not use an apostrophe to indicate the plural of a name. Do not use an apostrophe in the name of an organization in which the qualifying term is used as an adjective or an attributive rather than a possessive. Of course, always follow the official name.

Use ’s to indicate the plural of letters, signs, or symbols spoken as such or words referred to as words when s alone would be confusing. Note the italics with inflectional ending in roman type for words, letters, and numbers but not for symbols and signs.

He uses too many and’s.

The manuscript editor was mindful of the list of do’s and don’t’s.

Mind your p’s and q’s.

There are 9 +’s on the page.

His 1’s looked like 7 ’s.

The 3 A’s of rhinoplasty: anatomy, aesthetics, and architecture

Do not use an apostrophe to form the plural of an all-capital abbreviation or of a numeral (including years) (see 9.6, Plurals, Abbreviations).

8.7.6 Units of Time and Money as Possessive Adjectives.

With units of time (minute, hour, day, month, year, and so on) used as possessive adjectives, an ’s is added. (Note: For the plural units, add an ’ after the s.) The same holds true for monetary terms:

8.7.7 Prime.

Do not use an apostrophe where a prime sign is intended (see 14.4.4, Nomenclature, Drugs, Chemical Names).

The methyl group was in the 5′ position.