What's the Difference Between that and which?
An Example
Both are correct
- Please go into the room and get me the big book, which
is mine.
- Please go into the room and get me the big bookthat
is mine.
Both of these sentences would be incorrect:
- X Please go into the room and get me the big book
which is mine. X
- X Please go into the room and get me the big book, that
is mine. X
Notice the commas--that's what makes all the difference.
The Explanation
For example, imagine you have one sister, and you are telling a friend that
your sister is coming to visit you. Since this person is your friend, we can
presume that he knows that you have only one sister.
You utter a sentence like this to your friend :
- "My sister, who just graduated from college,
is coming to see me."
since your friend (we presume) knows you well and knows that you have only one sister, this extra bit of information is considered unnecessary
to identify which sister it is you are talking about. It is a sort of "by
the way" information--"My sister is coming to see me, and oh, by the
way, she just graduated from college."
Now imagine you have two, three, or even more sisters. Let's imagine that one is a college professor, another is a webmaster, and this one who is coming to visit you just graduated from college. If you're talking to your friend, and you say only "my sister," and you do not mention her name, your friend might not know which sister you are talking about. So you add that extra bit of information--my sister who just graduated from college--to identify which sister it is you are referring to.
In this situation, we have just correctly employed a very important grammar rule. Read on.
So, if the person you're talking to, or the person who's reading what you've
written, needs that extra bit of information to know which noun you're referring to, we say that that extra information is
non-restrictive. This word doesn't really describe the function clearly, so many teachers say that this information is "extra."
On the other hand, if you need that information to know which noun you are talking about, we say that the information is
restrictive. Again,
this word is not really a good choice for clarity, and many teachers use the
term "necessary information" instead.
Finally, just to make English a bit more difficult, we have a rule that says
we should use a comma before or after "extra information clauses and phrases," but not with "necessary information clauses or phrases." The idea
here is that the comma represents the slight pause in speech or change in intonation that a native speaker might use when making such an utterance.
I should point out that both
that and
which are relative pronouns,
i.e., they are grammatically the same, but their meanings are slightly different.
Now, let's return to our original example sentences:
- Please go into the room and get me the big book, which
is mine.
In this sentence, the clause
which is mine is "extra" because the information "the big book" is enough to identify which book it is that you want. We can assume that there is only one big book in the room.
- Please go into the room and get me the big book that
is mine.
In this sentence, the clause
that is mine is "necessary" because
the information "the big book" is NOT enough to identify which book
it is that you want--it is probably the case that there are several big books
in the room, so I need to add the information "that is mine" to identify
which book it is that I want.
More Examples
A few more examples may help:
- I met with Bill Clinton, who is a lawyer.
The name
Bill Clinton is enough to identify which person I'm talking
about--
who is a lawyer is therefore extra information.
- I met with the man who is a lawyer.
In this case, "the man" is not enough information to identify which
person I'm talking about--
who is a lawyer is therefore necessary information.
- The Sun, which is the only star in our solar system, is the source of heat for Earth.
Again, the name "the Sun" already clearly identifies the noun; therefore,
the information in the adjective clause "which is the only star in our
solar system" is extra.
- The star that is at the center of our solar system is called what?
In this case, since we don't have a name here, we don't know which star it is that we are referring to. Therefore, the information in the adjective clause "that is at the center our solar system" is necessary.
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Re: Learn Sentence Correction -
04-10-2006, 09:16 PM
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