Handout Topic: Which or that?

Which and that are often confused when used as relative pronouns introducing adjective clauses (although both may be used in other ways also). For example, in the following sentence, would you use which or that to fill in the blank?

  • The office _____ is next to the elevator is mine.

If you mean to specify (perhaps among several other offices) which office is yours, then you should use that. If, however, it is already clear from the context which office is yours, and the information you are adding about it being next to the elevator is simply extra information, you should use which.

The answer, then, really depends on what you mean to say, and so either which or that are possible in this example. But this is not always the case. As a rule, which should be used to introduce nonrestrictive clauses, and that should be used to introduce restrictive clauses. Grammar guides are starting to allow which to be used in both the restrictive and nonrestrictive sense (while still reserving that for restrictive cases), but for most academic writing, it is best to follow the traditional guidelines.

A nonrestrictive clause is essentially supplying non-essential information, while a restrictive clause is supplying information necessary to the meaning of the sentence.

e.g. #1 The chair, which is my father’s favourite, was found downstairs in the basement.

e.g. #2 The chair that is my father’s favourite was found downstairs in the basement.

The way the clauses in the above sentences are written changes the way the sentence is read. Because which clauses are nonrestrictive, we know that the information about the chair being the father’s favourite in the first example (#1) is non-essential. When the clause is introduced by that, however, it becomes restrictive. This changes the meaning of the sentence and indicates that it is necessary to specify which chair is being referred to (perhaps there were other chairs found downstairs as well). The second example suggests we could not identify the chair being referred to without knowing it was the father’s favourite; the first example is simply providing more information about the chair.

Notice that nonrestrictive clauses beginning with which are set off with a pair of commas (or a single comma if the clause appears at the end of the sentence).

  • The study rooms, which were locked at night, saw a lot of use during the exam period.