ACT® · English: Punctuation Conventions
That and Which
Use 'that' with no commas to pick one thing out of a group, and use 'which' inside commas to add a remark about something already identified.
These two words do different jobs because they attach to two different kinds of clauses. 'The car that I sold' narrows down which car you mean out of all possible cars - the clause is doing the identifying, so it needs 'that' and no commas. 'The car, which I sold,' already assumes you know which car; the clause just adds a side fact about a car that's already pinned down, so it needs 'which' and a pair of commas. Drop either clause and see what survives: drop the 'that' clause and the sentence loses its meaning, drop the 'which' clause and the sentence still names the same car.
On the test, this shows up as a choice between 'that', 'which', and sometimes 'which' with or without commas. Check first whether the noun is already specific - a proper name, a unique thing, something already described - or whether it's one item in a set still being narrowed down. If it's still being narrowed, 'that' with no commas. If it's already settled, 'which' with commas around the whole clause. 'Which' is never just a fancier 'that' in careful usage; swapping them changes whether the sentence is identifying something or commenting on it.
This topic connects to the rest of the punctuation unit because commas and dashes do the same identifying-versus-remarking work for other interrupters, like appositives and nonessential phrases. One wrinkle: after a preposition such as 'in', 'on', or 'to', only 'which' is grammatical ('the method in which', not 'the method in that'). There the comma question is separate - decide it the same way, by asking if the clause is still narrowing something down.
Key terms
- restrictive clause
- A clause that narrows down which specific item is meant; it takes 'that' and no commas.
- nonrestrictive clause
- A clause that adds extra, removable information about something already identified; it takes 'which' set off by commas.
- interrupter
- A word or phrase inserted into a sentence that can be removed without changing its core meaning.
- antecedent
- The noun that a pronoun like 'which' or 'that' refers back to.
Watch it explained
- How it worksHow does 'that' narrow a group down while 'which' adds a remark about a group already settled?
- Worked exampleWalk me through choosing between that and which for 'The trail ___ follows the river is closed.'
- Common mistakeWhy isn't 'which' merely the more formal version of 'that' in edited American writing?
- Going furtherWhat happens to the comma when 'which' comes after a preposition, as in 'in which'?
Check yourself
End of topic.