From a Guardian editorial of 14 November:
There is another lesson to the Petraeus affair. The former general fashioned for himself a role, which is much more significant than top generals have during wars. [screengrab]
Readers may briefly infer that what is “much more significant” is not a role but Petraeus’s fashioning a role for himself, or they may infer that top generals don’t normally have a role during wars. And then they’ll realise they’ve miscued because of a rogue comma.
The article should read “a role which [or that] is much more significant”. The clause led by which is restrictive, so there should be no comma before it.* Adding one makes the clause non-restrictive and obscures the antecedent – what the relative pronoun which refers to.
The ambiguity is quickly resolved, but it ought never to have arisen. Readers are being made to work unnecessarily for a straightforward point. Whether the comma came from the writer or from a sub-editor trained in the totally fake that/which rule, the sentence is unwittingly spoiled. Punctuation, instead of lending structure, has warped it.
The that/which rule is more typical of US style; elsewhere there is usually no problem with restrictive which. But the Guardian style guide includes the distinction, seemingly in the name of clarity and elegance. So the quotation above, though not a dire failing, is telling: it shows how communication is undermined through misguided deference to a bogus rule.
We can be grateful for the many other instances of restrictive which in the Guardian that have not suffered an intrusive comma. From today’s edition:
we don’t know what position we are going to have in a Europe which is much more tightly integrated as a result of the eurozone crisis.
Ostrovskaya was earlier cited as a critic of my book The Whisperers in the “controversy” which Ascherson mentions.
a picture published by the Sunday Sport which her lawyers described as a “fake up the skirt photo”.
All these phrases are fully grammatical and intelligible. They don’t need commas before which, nor do they need which changed to that.
If writers and editors are led to believe that a comma must precede relative pronoun which as a matter of correctness, some will adopt this erroneous edict and apply it incorrectly – a misstep apparent in the example up top, and in this Language Log post where Geoffrey Pullum calls the rule “a complete disaster”.
The that/which rule is a spurious invention that goes against the standard usage of centuries of good writing. It replaces judgement and grammatical awareness with uncertainty, anxiety, and mechanical behaviour. And the muddle is passed on to readers.
* My earlier post on the that/which rule explains the terminology and offers analysis, history, and commentary from usage authorities.