Dear Geist,

Can someone give me a quick simple rule of when to use which and/or that?

—Head Spinning, Prince George, BC

Dear Head,

The clause that follows the word which or that in the sentence will tell you which one to use. If the meaning of the sentence would change if you left out the that, you’d better keep the that. If the which just adds something to the clause without changing the meaning of the sentence, use which.

For language lovers, we’ll add two things. First, the lexicographer H.W. Fowler devoted two full columns of type to which in his seminal work Modern English Usage. Second, some of our favourite British writers use both which and that interchangeably for that, and it doesn’t seem to bother readers one bit.

—The Editors