The use of "which"

Question

Hello friends,
I have a simple question about the use of "which".
When I am using "which" as a pronoun, do I need to put a comma before "which"?
Example:
1. A third channel is provided by special recruitment agencies, which may be private enterprises or the.....
2. The presence of corporate managers and experts in less-developed countries can also contribute to the development of migration networks which encourge movements...

These two sentences are taken from the same article. In the first one, we use a comma before "which" and in the second, we do not.
So how do I understand if I need to put a comma before"whcih"?
Thank you in advance,
With Kind Regards,
Exciter

MrPedantic · Accepted Answer

Hello Exciter

If the 'which' clause adds new information about the noun it relates to, put a comma.

If the 'which' clause defines the noun it relates to, don't. (You can use 'that' instead of 'which' in such cases.)

MrP

Rolebra2005 · Answer

Thanks for the "that" reference, which (that) provides no clue.  "That" can be used in either sentence and, therefore, provides no clue or resolution to resolving the comma question.  Neither does "adds new information" as opposed to "defines the noun" clarify anything important in a determination of punctuation.  The clause in each case can be considered to do one or the either or both.

CalifJim · Answer

Here's another way to look at it.

Set the "which" clause off by commas when you consider it a parenthetical remark. Otherwise, don't use commas.

If I want to talk about a book, and it just happens that I bought it yesterday, then I use commas. The fact that I bought it yesterday is just thrown in as a less important element of the sentence.

"The book, which I bought yesterday, contains some very interesting passages."

If I want to single out a book as the one I bought yesterday -- not one I bought at another time -- I don't use commas. The fact that I bought it yesterday is important to showing which particular book I'm talking about.

"I have thoroughly enjoyed the last three books I've bought. But the book which I bought yesterday was the best."

CJ

MrPedantic · Answer

My last answer was rather woolly, and R2005 has rightly expressed some reservations.

Let me rephrase it, and expand on my defective 'that' comment, in the light of CJ's much better explanation:

'If the 'which' clause can be left out of the sentence, use commas. If it can't, don't.'

Applying this to CJ's sentences:

1. 'The book, which I bought yesterday, contains some very interesting passages.'

Here, the 'which' clause gives additional, non-essential information about the book, and can be omitted:

1a. 'The book contains some very interesting passages.'

'That' doesn't usually sit very comfortably as an alternative to 'which' in this structure:

'The book, that I bought yesterday, contains some very interesting passages.'

2. 'I have thoroughly enjoyed the last three books I've bought. But the book which I bought yesterday was the best.'

Here, the 'which' clause gives essential information about the book (it 'defines' the book), and so can't be omitted. If we do omit it, we get:

2a. ?'I have thoroughly enjoyed the last three books I've bought. But the book was the best.'

'That' sits usually sits very comfortably in this structure:

2b. 'I have thoroughly enjoyed the last three books I've bought. But the book that I bought yesterday was the best.'

(Some people say that 'that' should always be used in place of 'which', where the relative clause defines the noun, as in this instance. I myself am more inclined to 'trial by ear'.)

Interestingly, in #2, there's a second, hidden 'defining' relative:

2c. '...the last three books (that/which) I've bought.'

A 'defining' which/that can usually be omitted:

2d. 'The book I bought yesterday was the best.'

MrP

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