Write Clearly: Punctuation

An apostrophe is a punctuation mark used to create a contraction or to show possession.

When two words are shortened into one, the apostrophe replaces the missing letter(s). This combined word is called a contraction.

Examples:

• It is or it has = it's(i t apostrophe s)
• who is or who has = who's(w h o apostrophe s)
• they are = they're(t h e y apostrophe r e)
• will not = won't(w o n apostrophe t) [note change in spelling]
• is not = isn't(i s n apostrophe t)

However, note that contractions are usually not used in academic writing. Instead, write the full form.

When showing possession, add apostrophe “s” (’s) to the “owner” word. If the plural of the word is formed by adding an "s" (for example, cats), place the apostrophe after the "s" (see guideline #3 below). If the plural of the word is formed without adding an "s" (for example, children), add apostrophe "s" ('s) as you would to the singular form.

Examples:

• one table's (t a b l e apostrophe s)leg or several tables' (t a b l e s apostrophe)legs
• one student's (s t u d e n t apostrophe s)name or several students' (s t u d e n t s apostrophe)names
• one day's (d a y apostrophe s)work or several days' (d a y s apostrophe)work
• one woman's (w o m a n apostrophe s)job or several women's (w o m e n apostrophe s)jobs (note the plural form women does not use an “s”)

The exception to the possessive rule is that pronouns show possession without the use of apostrophes (e.g., my, mine, your, yours, his, her, hers, our, ours, their, theirs, its, whose, etc.).

Compare the use of apostrophes here:

• That is my book. That book is mine. (No apostrophe is used for the possessive pronoun “mine”)
• That is Bob's(Bob apostrophe s) book. That book is Bob's(Bob apostrophe s). (Apostrophe is used for the possessive noun “Bob's(Bob apostrophe s).

Compare contractions versus possessive pronouns here:

• They're(t h e y apostrophe r e) hoping to increase their budget.
• You're(y o u apostrophe r e) having trouble with your car.

If adding an apostrophe “s” would result in a double or triple “s” at the end of the word, erase the “s” after the apostrophe and leave the apostrophe in place.

Example:

• Sophocles'(Sophocles apostrophe) house, NOT Sophocles's(Sophocles apostrophe s) house
• Several bosses'(b o s s e s apostrophe) houses, NOT several bosses's(b o s s e s apostrophe s) houses

Note: Some grammar textbooks recommend keeping the "s's"(s apostrophe s) or "ss's"(s s apostrophe s) ending for singular words or for names ending in "s" or an "s" sound because this spelling allows for easier pronunciation.

Examples:

• James's(J a m e s apostrophe s) party, Marx's(M a r x apostrophe s) teachings, the boss's(b o s s apostrophe s) house, the class's(c l a s s apostrophe s) work, and congress's(c o n g r e s s apostrophe s) motion

The exception to the possessive rule is that pronouns show possession without the use of apostrophes (e.g., my, mine, your, yours, his, her, hers, our, ours, their, theirs, its, whose, etc.).

Compare the use of apostrophes here:

• That is my book. That book is mine. (No apostrophe is used for the possessive pronoun “mine.”)
• That is Chen's(Chen apostrophe s) book. That book is Chen's(Chen apostrophe s). (Apostrophe is used for the possessive noun “Chen's."(Chen apostrophe s))

Compare contractions using pronouns versus possessive pronouns here:

• They're(t h e y apostrophe r e) hoping to increase their budget.
• You're(y o u apostrophe r e) having trouble with your car.

As with other pronouns, the possessive pronoun “its” does not require an apostrophe. It is a common error for people to write "it's(i t apostrophe s)" for possessive when they should write "its."

To test whether to use “it's(i t apostrophe s)” or “its” in a sentence, read your sentence replacing “it's(i t apostrophe s)” with “it is.” If “it is” does not fit, the word you need is “its.” Note that there is no such word as “its'(i t s apostrophe)” with an apostrophe following the “s.”

Example:

• Correct: It's(i t apostrophe s) almost time to give the cat its medication.
• Or also correct, with contraction written in its full form: It is almost time to give the cat its medication.

Don’t use an apostrophe for plural nouns unless they are showing possession.

Examples

• Incorrect: Several students'(s t u d e n t s apostrophe) went to the meeting.
• Incorrect: The Smiths'(S m i t h s apostrophe) are on vacation.

Don't use an apostrophe for uppercase letters used as words.

Example:

• He received mostly As (capital A s with no apostrophe)on the papers marked by TAs.(capital T capital A s with no apostrophe)

Don't use an apostrophe for abbreviations.

Example: 

• The CEOs of each provincial office meet annually in Regina.

Don't use an apostrophe for numerals used as nouns and for decades.

Example: 

• All I have in my wallet are 10s and 20s.
• Technology advanced greatly in the 1990s.

Note: The exception to this rule is for lowercase letters used in the plural

Example: 

• Dot your i's(i apostrophe s) and cross your t's(t apostrophe s).