Can someone please clarify the strategy to use for "that vs. which" sentence correction problems. I know that one is restrictive and one is not, but I'm not sure what that means. Also, is it true that on the majority of GMAT questions, "which" is proceeded by a comma?

Thank you.

check this

Which vs. That
Property of the Regent University Writing Center Material is borrowed from A Writer’s Reference by Diana Hacker, 5th edition, pp. 239-241.
“. . . which . . .” or “,which . . .”
“Which” is used in both subordinate clauses and nonessential clauses. Within subordinate clauses,
“which” is used in this format: Sentence 1 + which + sentence 2. With nonessential clauses, “which” is
used as follows: Sentence + comma + which + extra information describing the noun/pronoun.
Example 1 (subordinate clause):
Elizabeth set the alarm clock which she thought was the loudest.
In this example, the first sentence “Elizabeth set the alarm clock” is joined to the second sentence “she
thought [it] was the loudest.” The second sentence does have both a subject and verb, so it is
subordination. (Certain subordinate words require slight adjustments to the second sentence. In this case,
the pronoun “it” was removed when “which” was added because the second sentence becomes more
dependent upon the first.)
Example 2 (nonessential clause):
Elizabeth bought the loudest alarm clock, which was also the most expensive on the shelf.
In this example, the main message and meaning of the sentence is “Elizabeth bought the loudest alarm
clock.” The phrase “which was also the most expensive on the shelf” is not a sentence—it is just a phrase
that describes the loudest clock. It is nonessential information, however, because if the information was
removed, the main message and meaning of the sentence would not be changed.
“. . . that . . .”
“That” is used in both subordinate clauses and essential clauses. Within subordinate clauses, “that” is
used in this format: Sentence 1 + that + sentence 2. Within essential clauses, “that” is used as follows:
Sentence + that + critical or necessary information describing the noun or pronoun.
Example 1 (subordinate clause):
Elizabeth needs to buy an alarm clock that she can depend upon.
In this example, the first sentence “Elizabeth needs to buy an alarm clock” is joined to the second
sentence “she can depend upon [it].” Again, the second sentence has both a subject and verb, so it is
subordination. (The slight adjustment—removing the extra “it”—helps to make the sentence smoother.)
Example 2 (essential clause):
Elizabeth needs to buy an alarm clock that is loud enough to wake her up.
In this example, the information “Elizabeth needs to buy an alarm clock” does not convey the entire
meaning of the sentence. Elizabeth does not need to buy just any alarm clock. She needs to buy an alarm
clock “that is loud enough to wake her up.” In this instance, the information following “that” is not a
sentence—it is a phrase that provides information that is critical to the meaning of the sentence. If the
information was left out, the sentence could still work and be grammatically correct, but the meaning
would be altered. This makes it an essential clause. :D

The sentence correction strategy guide does a great job explaining this.

"Which" is non-essential and "that" is essential.

Your decision on which one is appropriate is entirely based on whether the modifier you are creating is essential or not essential to understanding the meaning of the sentence.

"The house I live in, which is near the sea, is the same home that I grew up in." - To understand this sentence you didn't have to know that I lived near the sea. Or in order for the the second part of the sentence, "is the same home that I grew up in" to make sense you didn't have to know the "which is near the sea" part of the sentence. Hence, it's a non-essential modifier --> use which.

The opposite situation is when you have a sentence and the part of the sentence that/which has the modifier is essential to the meaning of the sentence. (This sentence the choice should be that.) More or less using 'which' makes the modifier that follows not essential to understanding the meaning of the sentence. Additionally, the use of 'that' typically takes away a comma since you are incorporating an essential component of an existing sentence.

Another example. We're on the phone and you're trying to find my house.

I say, "Look on your left-hand side, and it's the third house, which is red."

Or, I say, "Look on your left-hand side, and it's the third house that is red."

You look down the street and, in order, these are the colors of the houses you see on the left:
red, white, red, blue, red

Which house is mine? If I said the sentence using "which," then the middle house is mine. I told you my house is the third house, and I also happened to mention that it's red.

If, however, I said the sentence using "that," then the last house is mine. I told you that my house is the third red house, not just the third house.

Make sense?

_________________
Stacey Koprince
Instructor
Director of Online Community
ManhattanGMAT

Hi, saintjingjing - did you have a question? It looks like you copied my post but didn't add your own question.

Also, this thread is from a long time ago when we didn't have the same folder definitions and rules that we do now. Questions about specific grammar topics should be posted in the GMAT Verbal folders - in whichever folder is appropriate for the source. (I'd put this conversation in the Strategy Guide folder because we're discussing a grammar rule that is discussed in the strategy guide.)

So here's what to do: post again but post in the Verbal Strategy Guide folder. You can copy my original post from here and then paste it into your new post along with your question.

_________________
Stacey Koprince
Instructor
Director of Online Community
ManhattanGMAT