How to Use Apostrophes Like a Pro

This month, I’m back on the topic of punctuation marks. Whose turn is it this time? Apostrophes. These little marks are used in a few ways, but the main two are (1) to indicate missing letters in contractions (such as “don’t” or “they’ll”—not the pregnancy kind of contractions) and (2) to indicate possession (that something “belongs” to someone or something). This lesson focuses on the possessive use.

Let’s start with a slight tangent. If something is plural, we typically add an s to the end of the word, and we don’t add an apostrophe.

Which of the following patients is most at risk for inaccurate serum LDL and HDL cholesterol measurements?

This is one of our lead-in questions that lists four possible choices. Since we’re talking about more than one patient, we say “patients”—no apostrophe needed. Same with “measurements.”

That’s easy! Now on to possessives and apostrophes.

When we want to show that something belongs to someone (or something) else, we typically add ’s to the end.

The resident’s EM board review session was productive.

The EM board review session belongs to the resident, which is why we add the possessive ’s.

Asplenism secondary to sickle cell disease increases a patient’s risk for what type of infections?

The risk belongs to the patient, so we’ve again used the possessive ’s.

That’s pretty straightforward. But what if a plural word is possessive? Do we still add ’s to the end? Nope! Just put an apostrophe after the final s.

He has been caught smoking cigarettes in the ED bathroom and has been known to steal food trays and other patients’ belongings.

Note that it’s not patients’s.

Now it’s your turn—try this one out:

The [programs/program’s] OB/GYN [residents/resident’s/residents’] crushed their CREOG exam.

If you chose program’s (possessive of “program”) and residents (plural of “resident”), you’re correct!

Here’s a bonus apostrophe rule about the pronoun “it”: the contraction “it’s” means “it is,” but the possessive of “it” is “its”—no apostrophe in sight.

The apostrophe lesson’s examples are its most useful part. (Thanks, I make a lot of them up myself.) 

A possessive, a plural, and a possessive without an apostrophe—what an example!

By Laura Wilkinson

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Laura is a copyeditor and writer with Rosh Review/Blueprint Test Prep. She has a background in science and science communication (BS in Zoology, MS in Ecology & Evolutionary Biology, and Certificate for the Professional Sequence in Editing). She's passionate about making difficult concepts easy to understand. Outside of work, she loves to cook, bake, hike, and chase her kiddos around.