which

What, of those mentioned or implied.

• Which song shall we play?
• They couldn't decide which song to play.
• Which one is bigger?

The/Any ... that; whichever.

• Take which one you want.
• You may go which way you please.

Designates the one(s) previously mentioned.

• He once owned a painting of the house, which painting would later be stolen.
• She only speaks Chinese, which language I can hardly follow.
• For several seconds he sat in silence, during which time the tea and sandwiches arrived.

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

• Which is which?
• By now, you must surely know which is which.
• Which is bigger, the red one or the blue one?

The/Any ones that; whichever.

• Please take which you please.

In a non-restrictive relative clause, referring to something previously mentioned. Referring to a preceding noun.

• I dropped a saucepan, which knocked over the eggs, which went all over the kitchen floor.
• I found my camera, which I thought I'd lost, under the bed.
• I entered the room, at the far end of which was a small table.

Referring to a preceding noun.

• I dropped a saucepan, which knocked over the eggs, which went all over the kitchen floor.
• I found my camera, which I thought I'd lost, under the bed.
• I entered the room, at the far end of which was a small table.

Used of people (now generally who, whom, that; which remains possible with words also referred to by it such as baby, child).

• She had a young child, which cried incessantly.

Referring to a preceding statement.

• The front door was open, which concerned me.
• He had to leave, which was very difficult.
• She saved my life, for which I am eternally grateful.

In a restrictive relative clause, referring to a noun previously mentioned.

• This is the letter which I received.
• This is the letter in which he explains his decision.

Used of people.

Introduces an anacoluthon.

And; but.

• They only offered me five dollars, which I wouldn’t do it for less than fifteen.