I'm done or I've done
I'm done or I've done
When the class is over, our lecturer always says "OK, we're done." Is this sentence grammatically correct? Isn't it a passive form, which simply means we are done by sth./somebody? Can we use "we've done" instead in this case?
Yes. Done here means finished and has been used with this meaning since the 14th century, and no one batted an eyelid till 1917. It has been used by Dickens and Mark Twain amongst others, not to mention in the proverb:
Man's work lasts till set of sun, woman's work is never done.
See MWDEU - http://books.google.com/books?id=2yJusP0vrdgC&pg=PA361
Done here isn't treated as a verb, but as an adjective. According to OALD:
1 finished; completed
When you're done, perhaps I can say something.
Yes, it is grammatical, no, it isn’t passive and no, you can’t say *We've done instead. Done is an adjective meaning finished and the sentence is on the pattern Subject (We) – Verb (‘re) – Complement (done). (An alternative reading is to see the verb to be done as meaning to have done, to have finished, even though *We've done is not actually possible in the context you describe.)
The 're part is in place of the verb are (Which is the conjugated form for we of the verb to be), and we is the subject; done is an adjective meaning "complete, or "finished." So this statement is grammatically correct. We've done has a completely different meaning. The 've part is a conjunction of the verb to have and we. We've done is to say we have done, and we're done is the same as we are done. In this case it would only make sense to say we are done, so the professor is correct.
Is the phrase "fake teeth" correct? I googled it and found out that it is used. But my English tutor says that this phrase is incorrect and the book from Hillside Press had this phrase as a mistake.
So what is true?
Maybe your English tutor wants you to say "false teeth" instead. Google count is 85K for "fake teeth" and 442K for "false teeth".
Note that in the Wikipedia, both "false teeth" and "fake teeth" redirect to the page on dentures. However, in general, while "false teeth" is used as a synonym for dentures, "fake teeth" is more for things like vampire teeth that people wear in Halloween for fun.
Any language teacher that say a phrase is "incorrect" has no understanding of how language actually works. You can say that a term is more common and is the accepted way of saying a thing but if enough people use a word or phrase "incorrectly" then it becomes the accepted standard and the meaning changes. Language is not math and there are no "correct" answers. In language might makes right.