Common Grammar Mistakes: Which versus That.

Which versus That. (From-Paul V8 on Flickr.)

Knowing the difference between which and that can be a bit confusing. Which one do you use? That one? Okay, I’ll stop.

What makes matters worse is that there has been a shift in usage and definition over the last century. While you may not be using grammar books from 100 years ago, you’re more likely to encounter this change in literature as so many classics are over a century old.

So, which one do you use, and how can you tell the difference?

Ultimately, it boils down to the difference between two types of clauses.– restrictive and non-restrictive. A restrictive clause is one that limits or restricts the scope of the noun it is referring to. A non-restrictive clause, as I’m sure you can imagine, doesn’t. Here is what I mean:

The cheese that is stinky is delicious.
The cheese, which is stinky, is delicious.

In the first example, the clause “that is stinky” is a restrictive clause, because it limits the scope of the word “cheese”, as it is only referring to the cheese that is stinky. It isn’t referring to any other cheese except that one. If you remove the clause, you are only left with: “The cheese is delicious.” Without the clause, the reader no longer knows which cheese is being referred to and the sentence loses crucial information– not just any cheese is delicious.

In the second example, the clause is non-restrictive: the cheese’s stinkiness is additional information about a cheese being described. Basically, the clause which is stinky is here parenthetical —as in, “by the way, the cheese happens to be stinky.” It is an additional piece of information but it’s not essential to the sentence’s meaning.

Here’s another example:

Another great type of cheese is one that is blue-veined and harder than most.

The clause “that is blue-veined and harder than most” modifies and constrains “one”. Another great type of cheese is not just any other cheese but one particular type. The clause is restrictive,especially considering how little sense the sentence would make without it.

In terms of punctuation, there are two hard-fast rules to follow:

  • Restrictive clauses are not separated from the rest of the sentence by commas.
  • Non-restrictive clauses must be separated by commas from the rest of the sentence to indicate parenthesis.

This all seems fairly simple, yes?

Of course, I can’t end this blog post without listing a few exceptions to complicate things a bit. I don’t know about you, but I can certainly think of a few examples that defy the rules I’ve listed above, yet still make perfect sense. In fact, few writers have ever followed these rules systematically, and it’s easy to find examples where either relative pronoun is used with restrictive clauses. Here’s an example:

A vase which has lost its bottom is useless.

The clause which has lost its bottom is certainly restrictive; without it, you’re left with “A vase is useless” which you can agree makes no sense. Now, according to the traditional rules, which should instead be that. However, did you have any trouble discerning the sentence’s meaning? I’m guessing the answer is no.

It also comes down to a question of style. Granted, style is a bit harder to pin down as “it just sounds better” is hard to define as preferences to consonant stress and rhythm. (For the linguist geeks in the house, that provides a softer, relatively unstressed sound while which is harder and easier to stress.) . But, in certain instances, it does “just sound better” to use that instead of which. Here are a few examples; again, they don’t necessarily abide by the rules, but they are definitely points to keep in mind.

  • In clauses that follow impersonal constructions, such as it is, that is preferred: “It was the plant that fell”.
  • Clauses that refer  to the words anything, nothing, something, or everything have a slight preference for that over which: “Can you think of anything that still has to be done?”
  • Clauses that follow a superlative also tend to prefer that: “Thank you for the best night that I’ve ever had”.

By throwing these wrenches in, I’m not suggesting to completely ignore what I just said. After all, if that were the case, I would just delete this blog post entirely. What I am suggesting, however, is that language is fluid– yes, there are rules, but sometimes you can bend them a little– and you CAN use which instead of that sometimes, so long as your meaning is well-understood.

That being said, it doesn’t apply the other way around; non-restrictive clauses should always to start with which. That’s just the way it is. Likewise, the punctuation rules will always apply– non-restrictive clauses always need commas, but restrictive ones (whether you use that or which) don’t. Without the proper punctuation, your whole sentence can go awry and your meaning could get totally lost. So, if you do decide to bend the rules, you have to do so carefully. If you’re not sure (and it’s understandable if you’re not), then just follow the restrictive/non-restrictive rules I’ve first outlined above and you’ll be fine.



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