That versus Which
By Michael Becker
The difference between that and which, when used as relative pronouns, is one of those usage issues that most people think of as picky and unnecessarily pedantic. Yet mastering the subtle difference in usage between the two words can add a lot of punch to your writing and make the examples you use in your sentences clearer and easier to understand.
In the “Elements of Style,” William Strunk and E.B. White say the word that should be used as a “defining, or restrictive, pronoun.” The word which, conversely, is the “nondefining, or non restrictive” pronoun (p. 59).
The Chicago Manual of Style puts it thus: “that is used restrictively to narrow a category or identify a particular item being talked about… which is used nonrestrictively–not to narrow a class or identify a particular item but to add something about an item already identified” (5.202, p. 230).
Strunk and White give this example:
- The lawn mower that is broken is in the garage. (Tells which one.)
- The lawn mower, which is broken, is in the garage. (Adds a fact about the only mower in question.)
Their rule is to use which in cases where you’re adding extra information that does not need to be there to make the sentence understandable. Example 2 could stand without the which clause, but it adds something that would be nice to know before you go fetch the mower.
(When which is used like this, the clause containing it is almost always separated by commas, as in Example 2.)
Example 1, on the other hand, implies there is more than one mower, and the writer is specifying the broken one in the garage. The that clause is necessary to the meaning of the sentence.
Chicago also notes that which can be used restrictively, but typically when it is accompanied by a preposition. (…the situation in which we find ourselves…) In that usage, the which clause is usually not separated by commas.
Now, take the sentence I’ve just written as an example:
- Chicago also notes that which can be used restrictively, but typically when it is accompanies by a preposition.
In this case, the that clause (”that which can be used restrictively”) serves as the sentence’s direct object and is necessary for the meaning of the sentence. Without it, the sentence is very vague.
- Chicago also notes.
This kind of usage as a direct object is very uncommon using the word which.
Both style books note that the words are commonly switched and used indiscriminately (especially in British English), but they argue that polished American writers make the distinction and use the words accordingly.
About the author: Lauren Cerretti is the Graduate Writing Tutor at Montana State University in Bozeman, Montana.