Use an apostrophe to show that one noun belongs to another noun or proper noun. (In the phrases below, the possessive is bold and the noun that is owned is underlined.)

To show possession of compound (two or more) nouns/proper nouns, first determine whether the nouns are acting separately or together. Separate nouns are each marked with an apostrophe; joint nouns are only marked with a single apostrophe on the final noun.

• Example: After reading about Michael McMichael’s and Anthony Odom’s experience with the police, I could understand the police brutalization toward the community of color. (McMichael and Odom have separate experiences)
• Example: After reading about Michael McMichael and Anthony Odom’s experience with the police, I could understand the police brutalization toward the community of color. (McMichael and Odom share this experience)

Use an apostrophe when you combine two words or delete letters (often with helping verbs and negative markers).

Contractions are regularly used in speech and conversational writing but are often avoided in formal writing. To understand the conventions of your field of study, you can ask a professor or review academic writing in your discipline. However, it is always correct to use the non-contracted form. Some example contractions appear in the table below:

• Example: The Inupiat people of Alaska created a video game that’s (that + is) played in their native language.
• Example: Does it mean that you can’t (can + not) do something in the future if you couldn’t (could + not) do it before?
  
  (Note that the non-contracted form of can’t is cannot. There is a different meaning for the sentence “I cannot go to class” [I am unable to go to class] and the sentence “I can not go to class” [I am able to skip class].)

Use an apostrophe to abbreviate a year or decade of time. Most style guides recommend omitting the apostrophe for plural use of years and dates.

• Example: I was born in the ’90s/1990s. (not 90’s/1990’s)

Optional apostrophe: Style guides disagree, but you can use an apostrophe to refer to plural letters, numbers, and abbreviations. Check with your instructor or examine writing in your discipline, but be consistent with your choice. Using an apostrophe with lowercase letters is preferred over using an apostrophe with uppercase letters. It is also acceptable to use quotes instead of an apostrophe.

• Example: My name has two a’s (or “a”s, As, or A’s) in it.
• Example: I’ve been receiving 10s (or 10’s) on all my assignments.

Homophones are word pairs that sound identical but have different meanings, e.g. sight and cite. Like any homophone pair, these possessive/contracted homophones are indistinguishable when spoken but must be written correctly to avoid confusion.

The first version (its, your, whose, etc.) is a possessive determiner and the second (it’s, you’re, who’s, etc.) is a contraction. If you can expand the word to its two-word form, it’s a contraction. If you can’t, it’s a possessive determiner.

• Example 1: Rosseta (a robotic probe) finally landed on a comet after bouncing off its surface.
• Test 1: *Rosseta finally landed on a comet after bouncing off it is surface. (Ungrammatical = not a contraction. It must be a possessive determiner.)
• Example 2: It’s a proven fact that humans cannot fly.
• Test 2: It is a proven fact that humans cannot fly. (Grammatical = contraction.)