I have a vendetta against the overused and abused word that. It is often thrown in to help essays meet page length requirements or by those terrified of using other ways to connect ideas. I’ve never had a problem with which. I was delighted to learn when to use that or which, but I was interested in the history behind these choices. Unfortunately, or perhaps fortunately for a recent class assignment, I now also have opinions on the use of which as well.

According to this very entertaining Merriam-Webster article on that and which usage (Links to an external site.), this delineation was ignored in the mid-17th century before the usage of that became unpopular for several decades. Then wise grammarians in the early 20th century tried to lead us all down a better path and were pretty much ignored by most writers. Although it’s great as a tool while learning the nuances of grammar, I think which can be used with a restrictive clause if it’s adding to the details of the particular noun or pronoun the clause is focused on.

Which, like all great power, should be used responsibly.

Non-restrictive

Commas around a non-restrictive clause, which is one not pertinent to the preceding noun, are often the signs of that clause starting off with which.

• Correct: My book, which was a gift from my Dad, has a torn cover.
• Incorrect: My book that was a gift from my dad has a torn cover.

This makes sense to me and just looks correct. Which is easily the choice and the commas make it even easier to identify.

Restrictive

These are the bizarro versions of aptly named non-restrictive clauses and are pertinent to the preceding noun and complete the sentence. These are where that makes sense.

• Correct: The book that lies on the table.

The correct sentence specifies the specific book (the noun) I am referring to and what it has (the verb.) “Oh, that book.”

If I switch the that out with which, it does not have the same specificity. I can see how this would be seen as incorrect as it seems to start something more about the noun it follows and then just stops at the end of the preposition.

• Incorrect: The book which lies on the table.

However, when which is in front of the noun or pronoun in a restrictive clause, it cannot be switched out for that so easily.

• Correct: He didn’t tell her which book he checked out.
• Incorrect: He didn’t tell her that book he checked out.

Which is adding in that he had a selection of books to choose from. When that is used, it makes it seem more specific, which works when speaking on a very specific noun or pronoun but doesn’t make sense in the above example.

Like all good grammar “rules,” it comes down to clarity and what makes the most sense for the readers you’re writing for.