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)
- 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.Like it? Share it!