When to Use an Apostrophe to Form a Plural

The other day I encountered a headline that mentioned something about the different Doctor Whos, and it inspired me to write this post.

Do you know when to correctly use an apostrophe to form a plural?

If you’re following Chicago Style, the answer is:

Lowercase letters
Capital letters when necessary to avoid confusion
Symbols
Single-digit numerals
Lowercase abbreviations
Capitalized abbreviations with periods

So, returning to the headline I mentioned, “Doctor Who” requires no apostrophe to make it plural. It’s just “Doctor Whos.” (The author of the headline was correct.)

If you need an editor to help you with punctuation rules like this, feel free to contact me. I primarily edit fiction, and my schedule is full for the remainder of this year, but I’d love to chat about working together in 2025 =)

Timothy