Dear Alesa: Comma Conundrum

Dear Alesa:

I am having one heck of a time understanding when to use a comma with the words “that” and “which.” Every time I type it, I seem to get it wrong. Please help!

Confused by Commas

Dear Confused:

That is a tricky comma rule, but once you know the basics, it will make more sense. The first thing we need to discuss is restrictive clauses. Restrictive clauses are described as statements that are necessary for identification purposes in a sentence. Restrictive statements/clauses typically use “that” and are not offset with commas.

Non-restrictive clauses are statements that are not grammatically essential to the meaning and central understanding of the sentence. They simply add supplementary information. Non-restrictive clauses typically use “which” and are offset with commas.


  • The ambulance that is at the emergency entrance still needs to be attended to. (There is more than one ambulance. The one that is at the emergency exit needs attending to.)
  • The ambulance,  which is at the emergency entrance, needs to be attended to. (There is only one ambulance and it needs to be attended to.)
  • The MRI machine that is in the emergency department is on loan from Seattle Grace. (The hospital has more than one MRI machine. The one in the ER is on loan from Seattle Grace.)
  • The MRI machine,  which is in the emergency department, is on loan from Seattle Grace. (The discussion is about a single MRI machine. It’s on loan from Seattle Grace.)

I hope this information helps.


Alesa Little, MTE
Medical Transcription Editor Instructor

Related Posts

Leave a Reply

Your email address will not be published. Required fields are marked *