Expect a “Which” in Three Different Contexts
First, you must be ready for “which” to rear its head in three different contexts:
“Which” is a relative pronoun: “I want to buy a shirt, but I don’t know which.” It “relates” back to the word “shirt.” It is also a relative adjective: “I’m deciding which shirt to buy.” If this is not clear, look over the sentences and ask why “which” is a pronoun in the first example and an adjective in the second.
“Which” is an interrogative pronoun: “Which do you want to buy?” It is also an interrogative adjective: “Which shirt to you want to buy?” This application is parallel to its usage as a relative pronoun/adjective, so it should raise no new issues for you.
Now, let’s start swimming in the deep end of the pool: “Which” is also a perfectly good subordinating conjunction. Remember, a conjunction introduces a clause. Remember that a clause (unlike a phrase) has both a subject and a predicate. Unlike an independent clause, a subordinate clause does not express a complete thought; that is, it needs to attach to an independent clause in order to make good sense. Here is an example:
“The engagement ring, which I bought and paid for, looks great on your hand!”
Here we introduce another shady grammatical character, “that.” Just like “which,” “that” can come disguised as a pronoun (“I don’t want that“) or as an adjective (“I want that one“). Technically, “that” serves in this way as a demonstrative pronoun or adjective (i.e., it points things out). And, just like “which,” it can also appear as a subordinating conjunction.
Could you just as easily say, “The engagement ring that I bought and paid for looks great on your hand!“? Of course you can; but (as explained below) you would be conveying a meaning distinct from the first appearance of the engagement ring, above.
Which Subordinating Conjunction?
Welcome to the world of restrictive and non-restrictive clauses. In describing some noun (or pronoun):
- A restrictive clause provides information to narrow down the possibilities (i.e., “restrict” the choices) to the noun (or pronoun) in question. Without a restrictive clause, the hearer might not know which one out of several possibilities the speaker is discussing.
- A non-restrictive clause does not need to help identify the noun because both the speaker and the hearer already can uniquely identify which item is the topic of discussion. A non-restrictive clause simply adds additional information.
This distinction is used most often in the context of a rule for commas:
- A non-restrictive clause is set off with commas. Think of a non-restrictive clause as a kind of apposition — additional or optional descriptive information.
- A restrictive clause is not set off by commas, as the information is part of the complete specification of the subject.
Look at the two previous examples:
- The engagement ring, which I bought and paid for, looks great on your hand!
- The engagement ring that I bought and paid for looks great on your hand!
The first sentence uses a non-restrictive clause. It conveys a meaning something like the following: “Your ring, which (by the way) I bought for you, looks really good on your hand. (Don’t forget who footed the bill for that ring!)”
The second sentence uses a restrictive clause. It conveys a meaning like the following: “The ring that I bought you (as opposed to that other ring that some other guy bought you) looks really good on your hand. (I’m glad you decided to wear mine, and not that other guy’s ring!)”
What does this have to do with “which” and “that?” you ask. Over the centuries, English-speakers have used “which” and “that” interchangeably between restrictive and non-restrictive clauses. You will notice, however, that in the two examples above, “which” is used for the non-restrictive clause and “that” is used for the restrictive clause. This is a fairly modern convention, adopted probably a little over a century ago. In the well-respected little book, The Elements of Style (known also as “Strunk & White,” now in its 4th edition), the authors make the distinction described here, and counsel us that it is wasteful to have two perfectly good words that exercise the same, identical function; we should therefore give them separate syntactical chores.
And so it is: Let’s say you must call upon a subordinating conjunction to relate a subordinating clause to a noun (or pronoun) in an independent clause:
- Use “which” (with commas) if simply adding descriptive material; or
- Use “that” (without commas) if you must help to identify more precisely the item being discussed.
“Who” Causes Problems?
By the way, the same comma rule for restrictive and non-restrictive clauses also applies to clauses introduced by “who.” Remember, “who” is used for persons; “which” and “that” are reserved for things. Fortunately, “who” is your only choice, so there is no problem similar to the “which/that” issue. (On the other hand, you have a “who/whom” decision to make, but that’s for a different page). So, when the “who” further defines or identifies your person (restrictive clause), there is no need for a comma. When the “who” provides additional or optional information (non-restrictive clause), commas must appear:
Restrictive Clause: Two men walked out of a bar: a sober one and a drunk one. The man who was drunk tripped over his feet.
- Non-restrictive Clause: A man and a woman walked out of a bar. The man, who was drunk, tripped over his feet.