When to use which and when to use that is pretty darn confusing for most people. Many of us use the ‘does it sound right?’ rule. Or we use that when we’re being informal and which when we’re being formal. Or sometimes we don’t give a hoot and use that or which interchangeably.
It’s pretty subtle but the rule is as follows:
We use which when we’re adding information.
The books, which have green covers, are new.
So all the books are new. And we’re just letting you know they have green covers as an extra bit of information.
On the other hand, we use that when we are restricting information.
The books that have green covers are new.
We’re being very specific. Only the books that have green covers are new.
Clauses containing which are set off by bracketing commas. Which means they can be removed from the sentence and still make sense.
The books, which have green covers, are new.
The books are new.
So to recap. If you’re adding a bit of extra information, just for the heck of it, use which. Otherwise use that. Simples.
Rob Dobson is a freelance SEO Consultant. He works with clients directly or via design and development agencies. He has worked for South West Trains, PayPoint, MTV, SITA, and Sanderson as well as many SMEs.
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