If A and B are not the same, it is correct to say that A differs from B.

Which is correct, though, A is different from B, or A is different to B?

I've never heard an American speaker say different to, though I've read it in British authors. Here, we sometimes say different from and sometimes different than. Some people seem to think there is a distinction in meaning between these last two. If there is, it is a distinction without a difference to me.

I'd like to point out that where different to does occur in American speech, it has an entirely different sense than in the phrase Ewood intends. You could get, for example, "Afterwards, things were entirely different to Max." In such a construction, the prepositional phrase acts as a modifier, and can be omitted: Things were very different; they were never thereafter the same. In the phrases different from B and different than B, there is really no prepositional phrase modifier at all. Rather, different from and different than are each themselves constituents taking B as a complement.

I was always taught that the correct term is "different from."

"Different from" is stating a fact.

If you use "than" then you should actually have something to compare, as in "A is more different than is B" or "B is less different than is A."

But if you want only to point out the fact that they are different, you would say "A is different from B."

Strunk&White say 'one thing differs from another; therefore say different from.

Oxford Universal Dictionary allows different from, to, or than.

I think this usage, different to, is analagous to 'contrary to'.

My thanks to everyone. This bears out what I thought, but wasn't sure about, that 'is different from', being just another way of saying 'differs from', is the fundamentally correct way.

'Different than' (not more or less, just different) sounds wrong to my British ears, and appears to be an American construction, while 'different to' is a British abnormality - other than the particular case mentioned by Maiku.

'Different than' can be used when it is followed by a clause

e.g. Today the cause of individual freedom is different than it was in Homer's day.

It is not correct to use 'different than' followed by a noun or short phrase.

Ewood: I agree that the "different to" usage is strictly British. Whether it is anomalous there I can't say. The last time I met it was in a novel by Ruth Rendell, a very respectable writer from the U.K., even if most of her books are sometimes dismissed as mere "thrillers."

Babthrower: It is true that "different than" is preferred before whole clauses. "Than" is felt to have the force of a subordinating conjunction here, so no other clausal complementizer is required. But please note that "from" can also occur here, if there is also an appropriate complementizer, e.g., "The linguistic facts could turn out to be different from what you suppose."

Your assertion that it is "not correct" to use "different than" before simple noun phrases is simply observationally inadequate. Such expressions occur every day in acceptable American English. I myself would have no hesitation in writing, for example, "My observations are different than yours." You don't have to like it, but it happens. Was your teacher named Miss Fidditch, by the way?

Yes, Maiku, and she had magic powers. Of course we know that many expressions are well understood and used colloquially even though the grammar police don't like them. Still, we should keep an eye peeled for time-tested rules: there is usually a lot of thought behind them.