SAT® · Reading and Writing: Boundaries — Within Sentences
Relative Clauses and Whether They Take a Comma
A relative clause gets commas when it adds extra, droppable information about something already identified, and gets no commas when it's the only thing telling you which noun is meant.
Relative clauses are the who, which, that, whose chunks that hang off a noun to describe it. The punctuation question is never about grammar in the abstract; it's about whether the noun needs that clause to be identified. If the noun is already specific enough without the clause, the clause is just bonus material, and bonus material gets boxed off with a comma on each side. If the noun is vague or generic until the clause narrows it down, the clause is load-bearing, and load-bearing information takes no commas at all.
The test for this is deletion. Cross the clause out and read what's left. 'The Brooklyn Bridge still carries traffic' still names one exact bridge, so the clause describing when it was built is extra, and it gets commas. 'The one was closed for six months' names nothing, so the clause 'that was built in 1883' has to stay unpunctuated, because it's the only thing doing the pointing. Proper names almost always pass the deletion test on their own, since a name is already as specific as a noun gets, which is why clauses attached to names are usually comma-set-off.
This is also why the that-versus-which choice is a distraction on these items. Swapping the relative pronoun doesn't change whether the information is identifying, so the actual decision is still the comma placement, not the word choice. Within the larger boundaries topic, this sits alongside dashes and parentheses as another way English marks off information that could be lifted out of a sentence without breaking its core claim.
Key terms
- Relative clause
- A clause that describes a noun using who, which, that, or whose.
- Identifying clause
- A relative clause that is necessary to tell which specific thing is meant, so it takes no commas.
- Extra (nonessential) clause
- A relative clause that adds optional detail to an already-specific noun, set off with commas.
- Deletion test
- Removing the clause to see if the noun is still clearly identified, which reveals whether commas are needed.
Watch it explained
- How it worksHow do you test a relative clause by deleting it and asking whether the noun is still pinned down?
- Going furtherWhat changes when the relative clause attaches to a proper name instead of a common noun?
- Common mistakeWhy isn't 'that' versus 'which' the thing the digital SAT is actually asking about in these items?
- Worked exampleWalk me through punctuating 'The bridge which was built in 1883 still carries traffic' both ways.
Check yourself
End of topic.