That vs. Which: When to Add Commas

Comma use seems to confuse almost everyone at some point.

Equally confusing for many is when to use that and when to use which when introducing extra information in a sentence. They aren’t interchangeable: which requires a set of commas, and that does not.

This post tackles both questions. Answers are based on whether the additional information is essential or nonessential to the meaning of your sentence.

Essential Clause or Phrase

An essential clause or phrase is considered necessary to understand the full meaning of a sentence. Essential clauses generally start with that, and they are not set apart with commas.

The rake that is broken is in the bin for trash pickup.
(essential: tells which rake is in trash bin and why)

Dogs that bark a lot are not welcome in my neighborhood.
(essential: tells what kinds of dogs are not welcome)

These shoes that don’t have insoles are uncomfortable for walking.
(essential: specifies what makes shoes uncomfortable)

Nonessential Clause or Phrase

A nonessential clause or phrase is considered unnecessary to understand the full meaning of a sentence. Nonessential clauses generally start with which and are set apart with commas.

The rake, which Jay was using, is in the bin for trash pickup.
(nonessential: user of rake irrelevant)

Dogs, which require a lot of exercise, are not welcome in my neighborhood.
(nonessential: how much exercise dogs require irrelevant)

These shoes, which don’t have insoles, are on sale.
(nonessential: shoes on sale regardless of no insoles)


To Summarize:

  • Use that without commas to show that extra information is essential to the sentence.
  • Use which with commas to show that extra information is not essential to the sentence.
  • Reread your sentence to be sure it conveys what you intend.

Does everyone follow this grammar guideline? No.

Academic writing often uses which with essential clauses, and the British commonly use which with essential clauses. Some people might think using which sounds more refined in cases where using that would be more grammatically correct.

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Kathy Watson

Kathy Watson has a love/hate relationship with grammar; she loves words and the punctuation that helps them make sense, yet she hates those pesky rules. A self-proclaimed ruthless editor, she prefers standard usage guidelines of The Associated Press Stylebook. Her easy-to-use Grammar for People Who Hate Rules helps people write and speak with authority and confidence. She encourages and welcomes questions and comments. (Email)

3 thoughts on “That vs. Which: When to Add Commas

  1. AvatarKT Workman

    In your opening sentences, you state: “that requires a set of commas, and which does not.” Then later on, you explain and give examples that contradict this statement. I’m confused…

    1. Kathy WatsonKathy Watson Post author

      KT, thank you for your eagle eye! In one of my final editing sweeps, I reviewed the post and tried to be consistent in the sequence of when ‘that’ and when ‘which’ appeared. I inappropriately reversed the order in an explanation where is should have been the opposite.

      Another reader caught it, and I popped right in to correct the error. You were another astute early reader, and I appreciate your bringing it to my attention. I apologize for the tardiness of my reply.

  2. AvatarCharles Myhill

    Isn’t it funny? I knew this but couldn’t remember why ’till I read the blog. Thanks for the reminder, Kathy.

    Hope you’re well and enjoying Spring – at last.


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