Since Halloween is coming up, I thought you could use a refresher about “whiches”--more specifically, when to use a “which” and when to use a “that.”

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To understand the difference between “which” and “that,” first you need to understand the difference between a restrictive element and a non-restrictive element, because the simple rule is to use “that” with a restrictive element and “which” with a non-restrictive element. OK, don't worry; it's easy.

Restrictive Clauses and Nonrestrictive Clauses

A restrictive element is just part of a sentence you can’t get rid of because it specifically restricts the noun. Here's an example:

Desserts that contain chocolate please Squiggly.

The words “that contain” restrict the kind of desserts we're talking about. Without those words, the meaning of the sentence would change. Without them, we'd be saying that all desserts please Squiggly, not just the ones with chocolate.

Desserts that contain chocolate please Squiggly.

Restrictive elements aren't surrounded by commas.

Here's another example:

Jackhammers that don't have noise-dampening technology are on sale.

We can't get rid of the words “that don't have noise-dampening technology” because then we'd be saying all jackhammers are on sale, not just the special ones; so that means the clause is restrictive.

And another example:

Dogs that howl make me crazy.

I can't get rid of the words “that howl” because then I'd be saying all dogs make me crazy, not just the ones that howl, which isn't true.

On the other hand, a non-restrictive element is something that can be left off without changing the meaning of the sentence. A nonrestrictive element is simply additional information.

Chocolate desserts, which are his favorites, please Squiggly.

Leaving out the words “which are his favorites” doesn’t change the meaning of the sentence. With or without the words “which are his favorites,” we know that chocolate desserts please Squiggly.   Nonrestrictive elements are surrounded by commas.

Here's another example:

Jackhammers, which are useful for breaking up concrete, are on sale.

We could throw out the words “which are useful for breaking up concrete” and the meaning of the sentence wouldn't change. Those words are just extra, meaning they're non-restrictive, surrounded by commas, and “which” is the right word choice.

And another example.

Dogs, which make great companions, are usually furry.

Again, we could throw out the words “which make great companions” and not change the meaning of the sentence. Dogs are still usually furry. Those words, “which make great companions,” are just extra, meaning they're non-restrictive, surrounded by commas, and “which” is the right word choice.

A Quick and Dirty Tip? If you think of the Wicked Witch (Which) of the West from The Wizard of Oz, you know it’s okay to throw her out. You won’t change the meaning of the sentence without the whichphrase. So, you can throw out the which (or witch) clause, commas and all. If you can safely throw out the “which” and the meaning of the sentence doesn't change, then you know “which” is the right choice. If you try to throw out the clause and it does change the meaning of the sentence, then you know that the right choice is “that” instead of “which” because it's a restrictive clause. That's the simplified rule that I find works for a lot of people who get frustrated trying to decide which word to use.

“Which” Versus “That” – Advanced

There is a more complicated rule, and I'm going to explain it now, so if you don't want to hear it, stop listening for about 15 seconds.

OK, it's true that the word “that” can only be used for restrictive clauses, but some authorities maintain that “which” can actually be used for both restrictive and non-restrictive clauses. One problem with this is that many people don't know that “which” can be used for both. A second problem is that a lot of people follow the restrictive-non-restrictive “rule” that divides the two words, so it's safer to do it that way, since it's always an option anyway. I also believe it's a lot easier to remember the rule if you split “that” and “which” up along restrictive and non-restrictive lines. If you use the simplified tip that it's always safe to throw out the “whiches,” you'll always treat the word “that” properly; but if you love the sound of “which” and want to use it where I'd recommend a “that,” you'll find authorities to back you up, and people shouldn't go around thinking it's clearly wrong to use “which” for restrictive clauses.

“That” and “Which”--Relative Pronouns

I'll finish up with a little grammatical aside. When they're used in the way we've been talking about, “that” and “which” are called relative pronouns. I know it seems weird because you usually think of pronouns as words like “he” and “she.” Relative pronouns don't get talked about as much, but they are real pronouns. They head up subordinate clauses. Other relative pronouns include “who,” “whom,” “why,” “where,” and “when.”

Summary

To sum up, the simplest rule is to choose the relative pronoun “that” when you can't get rid of the clause and the relative pronoun “which” when you can get rid of the clause. Remember that it's always safe to throw out the “whiches.”

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