Quick question - when I was little, which was a looong time ago, I was taught never to start a sentence with and, but, because etc. Obviously people do, nowadays, but what about 'which'? I've seen it done often enough, but is it still strictly speaking frowned upon?

I'd say it depended entirely on what you were writing. I wouldn't use it in formal written English but I have definitely used it in writing fiction. To show a disjointed thought process. Or for comic effect.

Well obviously it's okay with a question:

Which of the dogs was ill?

I would do it in a non-question sentence, but only if I really wanted to emphasise it.

I went running along the road looking for the dog. Which was lost and had been missing for hours. I found her in a ditch

just makes the writer look ignorant. But - say -

So, we've proved that only person who could have killed John in Dover at least an hour before he was found at 4.15, was Alice. And we know that Alice was seen in a café in Honfleur at 6.45, so she must have taken less than two and a half hours to cross the Channel. Which is impossible.

might well work, because it suits the way that it would be said. Narrative in fiction always has one foot in how people actually speak, after all - and sentence structures have to reflect that, as well as grammatical correctness.

<Added>

Crossed with Jem. Yes, exactly.

Or for comic effect.

You're right, Jem. Starting with 'which' can usefully generate a comic or wry effect.

"...and our eldest son, Alexander, won the Nobel Chemistry Prize. So we all went over to Stockholm, for the presentation, and R.E.M. did an impromptu concert. Which was nice."

Which is from the Fast Show. More examples at
http://whichwasnice.webs.com/

Chris

Thanks folks, it's what I thought you'd say, but happy to have it confirmed. Too much editing shrivels the brain I think...

Even the start of sentence doesn't matter when you apply the creative writing rule... There are no rules, it either works or it doesnae. Which, when you think about it, makes sense. (At least to me). And why is that full stop outside of the bracket? Who cares if it comes with a microsoft green line. It looks better in colour.

Some examples?

Cheers
Michael