It's a which hunt

Q. A what

A. A which hunt: the conundrum of when to use 'which' or 'that' in subordinate clauses.

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Q. Subordinate clauses

A. A subordinate clause is one that requires the main part of the sentence to give it meaning, one which won't make sense on its own. An example of this would be: 'The car, which is blue, has alloy wheels'. The main part of the sentence is 'the car has alloy wheels'; the subordinate or qualifying clause is the extra information, the fact that the car is blue.

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The usage is intimately linked with the distinction which grammarians make between non-restrictive and restrictive clauses.

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Q. Restrictive

A. A restrictive clause is one which 'restricts' the meaning of the noun it is referring to. So to take the example above: 'The car, which is blue, has alloy wheels' is non-restrictive because the sentence works without the subordinate. However, 'the car that is blue has alloy wheels' is restrictive because it limits the scope of the word car, indicating that the writer doesn't mean all cars, only the one painted in that particular colour.

Style guides used to state categorically that non-restrictive clauses should be introduced by 'which' and must be separated by commas from the rest of the sentence to indicate parenthesis, while restrictive clauses should be introduced by 'that' and are not separated off from the rest of the sentence.

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However, things are less 'restrictive' these days.

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Q. How so

A. Because there are occasions when the two words are interchangeable and 'which' doesn't always have to be introduced by a comma. Any of you who use the grammar check function in Word will probably have noticed that it will always pick you up on a 'which' not preceded by a comma and offer you ', which' or 'that'. This is a rather simplistic way of looking at it.

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Despite the shift in usage, there remain some situations in which 'that' is still preferable to 'which'. For example: in clauses that follow impersonal constructions - such as 'it is' - 'that' is preferred (so 'it was the car that is blue'); clauses which refer back to the words anything, nothing, something or everything (so 'I like nothing about the car that's blue'); and finally, clauses which follow a superlative also tend to work better with 'that' (so, 'that's the bluest car that I've ever seen').

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Q. So it does matter

A. It's not for the most part problematic in spoken English - 'that is' contracts to 'that's', making it less of a mouthful that 'which is', so you may find that you'll naturally say 'that's' on occasions when you'd write 'which is', if you get the drift.

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Anyway, the rules have relaxed over the last century, so, apart from the instances mentioned above, you won't go wrong if you use 'that' for restrictive clauses and 'which' for others.

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This isn't simply a pedants' soapbox - honest.

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For more on Phrases & Saying click here

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By Simon Smith