The bridge that spans the Bow River which flows through Calgary is falling down.

WHICH VERSUS THAT

The word which can be used to introduce both restrictive and non-restrictive clauses, although many writers use it exclusively to introduce non-restrictive clauses; the word that can be used to introduce only restrictive clauses. Think of the difference between

"The garage that my uncle built is falling down."
and

"The garage, which my uncle built, is falling down."

I can say the first sentence anywhere and the listener will know exactly which garage I'm talking about — the one my uncle built. The second sentence, however, I would have to utter, say, in my back yard, while I'm pointing to the dilapidated garage. In other words, the "that clause" has introduced information that you need or you wouldn't know what garage I'm talking about (so you don't need/can't have commas); the "which clause" has introduced nonessential, "added" information (so you do need the commas).

Incidentally, some writers insist that the word that cannot be used to refer to people, but in situations where the people are not specifically named, it is acceptable.

The students that study most usually do the best.

(But we would write "The Darling children, who have enrolled in the Lab School, are doing well.")

Who, Whose, Whom, Whoever, Whomever

One of the most frequently asked questions about grammar is about choosing between the various forms of the pronoun who: who, whose, whom, whoever, whomever. The number (singular or plural) of the pronoun (and its accompanying verbs) is determined by what the pronoun refers to; it can refer to a singular person or a group of people:

The person who hit my car should have to pay to fix the damages.

The people who have been standing in line the longest should get in first.

It might be useful to compare the forms of who to the forms of the pronouns he and they. Their forms are similar:

	Subject Form	Possessive Form	Object Form
Singular	he who	his whose	him whom
Plural	they who	their whose	them whom

To choose correctly among the forms of who, re-phrase the sentence so you choose between he and him. If you want him, write whom; if you want he, write who.

Who do you think is responsible? (Do you think he is responsible?)

Whom shall we ask to the party? (Shall we ask him to the party?)

Give the box to whomever you please. (Give the box to him.)

Give the box to whoever seems to want it most. (He seems to want it most. [And then the clause "whoever seems to want it most" is the object of the preposition "to."])

Whoever shows up first will win the prize. (He shows up first.)

The only problem most writers have with whose is confusing it with who's, which looks like a possessive but is really the contraction for who is. In the same way that we should not confuse his with he's (the contraction for he is or he has), we should not confuse whose with who's.

Who's that walking down the street?

Whose coat is this?

I don't care whose paper this is. It's brilliant!

Whose can be used to refer to inanimate objects as well as to people (although there is a kind of folk belief that it should refer only to humans and other mammals): "I remember reading a book — whose title I can't recall right now — about a boy and a dog."