I’ve been spending an unreasonable amount of time this weekend thinking about the words that and which. Why? Because I have too much time on my hands.
In truth, whenever I have to mentally decide which one to use, I usually go with my gut, and there’s a common misconception that the two are interchangeable. But, there’s an actual rule, so put on your grammar pants, because we’re going to take a deep dive into the fun world of clauses.
Restrictive and Non-Restrictive Clauses
Okay, let’s get started! In English, a clause is a portion of a sentence that contains a subject and a predicate. What’s a predicate you might ask? It’s essentially the action that the subject is doing (usually with a verb). Basic, right?
Still with me? Now, a restrictive clause functions as an adjective to identify the word it modifies. A restrictive clause restricts, or is otherwise essential for the intended meaning and is not offset with commas.
The coworker that ate my pizza is in accounting.
You aren’t talking about any old coworker – you’re talking about the one who went into the lunchroom fridge, saw your name on that slice of pizza, and ate it anyways. In other words, essential information, and therefore, a restrictive clause.
A, non-restrictive clause, on the other hand, is a clause which is not needed to identify the word it modifies – think of it is as additional information. As a non-restrictive clause is not essential to the meaning of a sentence, it is offset with commas (or brackets, dashes, etc.)
My pizza, which I bought last night, is in the fridge.
Here, nobody cares that you bought it last night. Well, they might, which is why it’s additional information, but if you remove it, it doesn’t change the meaning of the sentence.
You might have shrewdly seen where the words that and which were placed above. Now that we know the difference between restrictive and non-restrictive clauses, let’s take a look at when to use each.
That vs Which
Let’s look at an example of how that and which aren’t exactly interchangeable.
The apartment that has two bedrooms is in the West End.
The apartment, which has two bedrooms, is in the West End.
These don’t mean the same thing! By noting that the apartment has two bedrooms as a restrictive clause and using that, you’re implying there are multiple apartments and you’re specifically talking about the one with two bedrooms. By using it is a non-restrictive clause and using which, you’re simply adding that it has two bedrooms as additional information.
The Golden Rule
Now, for the rule! If the sentence doesn’t need the clause that the word in question is connecting, (i.e. is a non-restrictive clause) use which. If it does, use that.
Or, in other words, if the information is essential to the meaning of the sentence, use that. If it’s not, use which. Simple, right?