NOT A TEACHER
(1) Many native speakers also ask this question.
(2) Here in the United States, many (not all) native speakers
follow this rule:
that for a restrictive clause (one that points out a specific
person, thing, idea, etc.) If you omit (erase) the clause, the idea
of your sentence is not what you wish to express.
which for a non-restrictive clause (one that gives an extra explanation
but is not absolutely necessary to the meaning that you wish to
(3) Mr. Walter K. Smart's English Review Grammar gives these
Any house that is burned will be rebuilt.
(If you delete (erase) "that is burned," you get: Any house will be
rebuilt. Now that is not true. Only a house that is burned will be
rebuilt. The other houses will not be rebuilt. Therefore, the clause
is restrictive. Some books use the word "defining.") Mr. Smart
reminds us that some speakers would feel comfortable using
"which" here. I believe that most American teachers prefer "that"
for restrictive clauses.
Chicago, which is the metropolis of the Middle West, is a great
If we delete the clause, we get: Chicago is a great industrial center.
And that is our main idea. ("Which is the metropolis of the Middle
West" is interesting but not necessary to the meaning that we wish
to express.) So that clause is non-restrictive.
(4) I have a suspicion that many teachers will say that "which" is
also fine in your sentences. And, of course, you must accept their
answers as the correct ones. Personally, however, I would use
"that" in all of your sentences. In other words, if a clause does
NOT need commas, use "that." If it needs commas, use "which."
Student or Learner