Posted by R. Berg on May 10, 2001
In Reply to: "Which" and "that," which one when? posted by Massimo Mazzucco on May 10, 2001
: This is probably too basic a question for English-speaking people, but I do have this problem quite often (not being one of them).
: Is there a basic rule (on when to use one rather than the other), or do you just "play it by ear?"
: Massimo Mazzucco
There is a rule, and most native speakers get it wrong anyway when writing.
"Which" for nonrestrictive clauses and "that" for restrictive clauses. That doesn't help much, because you always have to stop and think which kind of clause you have. Sometimes in my schooling, nonrestrictive clauses were called nondefining clauses, and restrictive cl's were called defining cl's.
A restrictive clause is one that restricts, or limits, the meaning of the word(s) it modifies.
-The pot that I made soup in is in the sink.
-Sentence without clause: The pot is in the sink.
-Clause: that I made soup in. This clause is defining because it singles out the pot among all possible pots.
A nonrestrictive clause does not limit the meaning of what it modifies.
-Sentence: The 3-quart aluminum pot, which was a gift from Grandma, is in the sink.
-Sentence without clause: The 3-quart aluminum pot is in the sink.
-Clause: which was a gift from Grandma. The pot is already identified ("defined") without the clause (assuming the household has only one 3-qt, etc., pot). So the clause is nondefining. It adds information but doesn't tell the listener which pot you mean.
If lifting the clause out of the sentence leaves intact the meaning of what remains, you have a nondefining clause.
A nonrestrictive clause should have a comma at each end. A restrictive clause shouldn't have a comma at either end unless something else about the sentence requires a comma there.
There are some exceptions.
1. With a nonrestrictive clause, if there are too many "thats" around, use "which" instead of "that" to avoid a jingly jangle.
-That's right, I believe that the pot WHICH I made that soup in that was oversalted is in the sink.
2. With two correlative clauses (they modify the same word), use "which" instead of "that."
-The pot WHICH I made soup in AND WHICH sprang a leak is in the sink.
3. Use "which" if the clause is so far from what it modifies that people would get lost looking for its referent.
-The pot from the set Grandma gave us last Christmas WHICH I made soup in is in the sink.
The usual mistake of writers is to use "which" when "that" is correct, not the other way around. I think they do that because "which" is associated with writing more than with speech and consequently has acquired an air of formality or correctness. "Which" occurs more often in writing, but not because it's a better word than "that"; it's because the kinds of clauses that properly take "which" are rare in speech.