Determiner

1. What, of those mentioned or implied (used interrogatively).

   Which song made the charts?

2. What one or ones (of those mentioned or implied).

   Which is bigger?

   Which is which?

3. The one or ones that.

   Show me which one is bigger.

   They couldn't decide which song to play.

4. the one mentioned

   For several seconds he sat in silence, during which time the tea and sandwiches arrived.

   I'm thinking of getting a new car, in which case I'd get a red one.

Pronoun

1. Who; whom; what (of those mentioned or implied)

   He walked by a door with a sign which read: PRIVATE OFFICE.

   Their first song, which made the charts in 2004, is great.

   We've met some problems which are very difficult to handle.

   He had to leave, which was very difficult.

   We have to protect the environment in which we live.

   No art can be properly understood apart from the culture of which it is a part.

Usage notes

• (US usage) Some authorities insist, prescriptively, that relative which should be used only in non-restrictive contexts. For restrictive contexts (e.g., The song that made the charts in 2004 is better than the later ones), they prefer that. Actual usage does not support this "rule." Fowler, who proposed the rule, himself acknowledged that it was "not the practice of most or of the best writers." Even E.B. White, a notorious "which-hunter," wrote this: "the premature expiration of a pig is, I soon discovered, a departure which the community marks solemnly on its calendar." In modern UK usage, The song which made the charts in 2004 is better than the later ones is generally accepted without question.

Quotations

• 1611 — King James Version of the Bible, Luke 1:1

  Forasmuch as many have taken in hand to set forth in order a declaration of those things which are most surely believed among us...