That Which Has a Tail

Someone recently asked me the difference between that and which. I stumbled through a response, knowing I wasn't doing an adequate job of it. Herewith, a (hopefully) better answer. By the way, if you speak the Queen's English, the answer is short and sweet: there is no difference. But if you speak American English, read on.

That is a relative pronoun used for restrictive clauses, clauses that are necessary to the meaning of the sentence. If you didn't have the clause, the sentence would mean something different. The clause restricts the meaning. For example:

I picked up the books that were on the table.

The books I picked up are limited to the ones on the table; I didn't pick up the ones on the floor or on the shelf.

Which is a relative pronoun used for nonrestrictive clauses, clauses that add detail to the sentence but are not crucial to the sentence's meaning. If the clause were taken out, the sentence would still make sense. The sentence's meaning is not restricted. For example:

I picked up the books, which were on the table.

When I picked up the books, they were all on the table; there weren't any on the floor or the shelf. That they were on the table is extra information.

Note the comma before which. If you've got a nonrestrictive clause, you need that comma and the which. They tell the reader some extra information is coming up. You can remember that the witch (which) has a tail (,):

Bryan Garner gives three guidelines for deciding if you need that or which (Garner's Modern American Usage, 806):

1. "If you cannot omit the clause without changing the basic meaning, the clause is restrictive; use that without a comma."
2. "If you can omit the clause without changing the basic meaning, the clause is nonrestrictive; use a comma plus which."
3. "If you ever find yourself using a which that doesn't follow a comma (or a preposition), it probably needs to be a that."

If it's still not clear, check out Grammar Girl's recent episode on that vs. which.

Back? OK, let's see if you've got it. In the following sentences from Grammar Smart by the staff of The Princeton Review (30), choose the correct pronoun:

1. The letter (that, which) came today was nice than the one (that, which) came yesterday.
2. Usually my mail, (that, which) is delivered at noon, is nothing but bills.
3. A letter (that, which) is full of compliments is a joy to receive.

Update: Answers are posted here.