At first glance, there might not appear to be a difference between that and which, two relative pronouns used to introduce a dependent clause in a sentence. But in careful writing, that and which have distinct uses that can drastically change the meaning of a sentence.
To be fair, writers in the UK may already be perplexed by this question, given that in British English, the words are more or less interchangeable. However, in North American English, there is a major distinction between the relative pronouns that and which.
What’s a Relative Pronoun?
Relative pronouns are used to introduce dependent clauses in a sentence, those clauses that cannot stand on their own, like:
| (1) | that everyone knows to be true. |
| (2) | which we enjoy. |
The relative pronouns that and which introducing those dependent clauses, like all pronouns, stand in for a noun or noun phrase that has been previously referenced:
| (3) | The color of the sky is a fact that everyone knows to be true. |
| (4) | After dinner, Rahima always bakes us a pie, which we enjoy. |
In the above examples, the nouns fact and pie are represented in the dependent clause by the relative pronouns that and which, respectively. Such sentences are really just a shorthand way of saying two separate thoughts in one sentence.
| (5) | The color of the sky is a fact. Everyone knows the fact to be true. |
| (6) | After dinner, Rahima always bakes us a pie. We enjoy the pie. |
So, what then determines whether to use that or which in a given sentence?
Restrictive versus Non-Restrictive Use
The difference between that and which is in the difference between the “restrictive” and “non-restrictive” uses of the dependent clause. That is, is the dependent clause attempting to restrict the meaning of the main clause or simply provide additional information? Consider the following two examples.
| (7) | Mei brought me the dictionary that was on the table. |
| (8) | Mei brought me the dictionary, which was on the table. |
In Example (7), Mei did not bring me just any dictionary; she brought me the dictionary that was on the table. The usage of the word that has restricted the meaning of dictionary to mean “the particular dictionary that was on the table and no other.”
However, in Example (8), the phrase which was on the table offers supplemental information that is not necessary for the meaning of the word dictionary. That is, the speaker’s thought would have been complete with Mei brought me the dictionary. The dependent clause which was on the table merely provides additional information about where the dictionary happened to be.
This distinction can feel like a fine distinction and one that, as mentioned earlier, our British friends aren’t even aware of. But there are cases in which the difference between that and which can really matter.
Clarity
As is often pointed out on this blog, clarity is the primary goal in good writing. All rules and guidelines should serve the purpose of clarity, and the proper use of that and which can aid clarity in communication.
For example, suppose a friend were to say, “Bring me the cake, which is in the fridge.” In response, you go into the kitchen and see a cake on the counter. You assume that this is the cake your friend meant because, as far as you know, there is only one cake. Your friend was simply mistaken as to where it was.
However, if your friend were to say, “Bring me the cake that is in the fridge,” and you saw a cake on the counter, you might not immediately assume that was the cake your friend had in mind. The use of the restrictive that is in the fridge suggests the possibility of other cakes not in the fridge that your friend does not want to be brought out.
Or take the following clauses from a legal contract:
| (9) | Contractor agrees not to disclose any information gained during the contract relationship, which Employer considers confidential. |
| (10) | Contractor agrees not to disclose any information gained during the contract relationship that Employer considers confidential. |
There is a great difference between these two clauses. In Example (9), the contractor is barred from disclosing any information. The dependent clause simply informs us that the Employer considers that information confidential.
However, in Example (10), the contractor agrees only to avoid disclosing information that the Employer considers confidential, which suggests that there is information the Employer does not consider confidential that can be disclosed.
Those are two very different circumstances, and a lack of clarity about the difference between that and which can get people into all kinds of trouble. Indeed, court cases have been decided based on distinctions even smaller than these.
So, as always, we come back to clarity. Knowing rules like the difference between that and which, which feels arcane at times, can help your writing to attain the excellence that you want.