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When is it appropriate to use 'that' as opposed to 'which'?

I can't figure out whether to use that or which:

"and initiate collaborative projects that will extend beyond the conference"

or "and initiate collaborative projects which will extend beyond the conference"


Both are semantically very clear. No difference in understanding.

As mentioned in the page http://www.thefreedictionary.com/which:

It is used to refer to a thing or things mentioned previously to distinguish it or them from others.


This is the book (which/that) you wanted.

Clearly, in the above context, any one could be chosen.

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    I think there are two schools of thought here- one that states the two are interchangeable and one that says they aren't. I am in the camp that says they aren't. Your example requires that. – Jim Oct 4 '12 at 6:30
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    which should be used to introduce non-restrictive clauses, that introduces restrictive clauses. If you can substitute 'which, by the way,' and it still makes sense then it is non-restrictive and should use which. If the purpose of the word is to distinguish the one you are talking about from others then it is restrictive and should use that. See Robusto's answer here: english.stackexchange.com/a/15216/17956 – Jim Oct 4 '12 at 6:46
  • I just checked the first seven results from this Google search, and not a-one of them said that the two words were interchangable in that context. Conversationally, I agree, most people wouldn't bother to correct you if you used the wrong word, and the meaning would be clear. Still, this answer is tenuous, in that it could easily create the impression that either one is correct, even in formal writing. – J.R. Oct 4 '12 at 8:10
  • @J.R. So the translators of the King James Bible and Franklin D, not to say the distinguished authors of 'The Cambridge Grammar', got it wrong? – Barrie England Oct 4 '12 at 8:40
  • @Barrie: I was careful not to say that. :^) I'm saying that of the two answers – yours and Neeraj's – which both point in the same direction, Neeraj's is more weakly substantiated. – J.R. Oct 4 '12 at 8:47

You can use either. Some people may tell you that only that is allowed to introduce a clause of that kind (a definining or restrictive relative clause), but that view is not supported by the evidence. For example, Render therefore unto Caesar the things which are Caesar's (King James Bible) and a date which will live in infamy (Franklin D Roosevelt).

As the authors of 'The Cambridge Grammar of the English Language' (using 'integrated' instead of 'defining' or 'restrictive') write:

Integrated relatives with which are grammatical in all varieties of English.

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