From the "Speaking Polite Japanese"/ "Polite Form and verb Stem" page:
I have heard on a number of occasions that the negative non-past conjugation as given here is not an "officially" correct conjugation. Instead, what's considered to be a more "correct" conjugation is to actually replace the 「ないです」 part with 「ありません」. The reasoning is that the polite negative form of the verb 「ある」 is not 「ないです」 but 「ありません」. Therefore, 「かわいくない」 actually becomes 「かわいくありません」 and 「静かじゃない」 becomes 「静かじゃありません」.
I agree that ない should become ありません in order to be the more gramatically correct polite conjugation. However, I don't think that that is the end of it. I have been taught that じゃ is in fact a contraction of では. Therefore, the truly correct polite version of じゃない is in fact ではありません。
The choice between じゃ and では is one of formality, not politeness. Although formal language tends to be considered polite, formality and politeness aren't quite the same thing. A conversation with a stranger on the street is an informal setting (since it's not a special occasion, and it's obviously not the written language), but one where you're expected to be polite.
It's kind of like English: you might greet an old friend with "What's up, ya old bastard?", but you wouldn't greet a stranger that way; you'd be more polite. But you'd have no trouble using contractions such as "it's" and "don't" with them, and in fact you may sound strange if you deliberately avoid them.
That said, I think ではありません is worth a mention because very many Japanese lessons use it, and it's very common. It's just less likely to be used in informal situations is all.
Last edited by furrykef (2009-09-23 01:55:32)