じゃ・では / Ja - de wa question
 

What's the difference between "ja arimasen" and "dewa arimasen"?

I was taught that "ja arimasen" is what's generally spoken, but not usually written and is more colloquial than "dewa arimasen" which is used more in writing.

～ます　～ません　です　でした etc. are almost never seen in writing unless quoting someone's written speech.

Here's from a news article today:
ロシアを訪問中のヒラリー・クリントン米国務長官は13� ��、モスクワでラブロフ外相と会談した。両外相は第１次戦略兵器削減条約（ＳＴＡＲＴ１）に 代わる新たな核軍縮条約の年内締結に向け交渉を加速す ることで合意した。
　会談後の共同記者会見でクリントン長官は新核軍縮条 約について「我々の目的はＳＴＡＲＴ１が期限切れとな る12月５日までに条約締結の作業を終えることだ」と発� ��した。ラブロフ外相は「大きな前進があった」と述べたが、 核弾頭の上限など具体的な内容には言及しなかった。

I know most text tends to use plain form, MMM, but the OP used 'masen' and the question was about the use 'ja' and 'dewa'.

I'll rephrase it then; I was taught that 'ja' is more usually spoken and less usually written and 'dewa' is the reverse.

If that's still wrong, then please let me know so I can add another complaint to the 'why my teacher needs to be fired' list.

Im JPnese.exactly.you are right.

I was taught the same way, Columbine. I don't think a native speaker would agree, though. Essentially they mean the same thing, and you could argue 'de wa' is more formal than 'ja', but they more than likely can be used interchangeably.

Thanks mate :)

There have been a few topics about this subject before. Nagoyankee has said that じゃありません is not/very rarely used. Now that I have a formal Japanese teacher (it's not a greatly difficult course quite easy so far, nothing I didn't know, but I need a high school level foreign language qualification to get into Japanese at university) she said じゃありません is not uncommon. She is also a native speaker. So I think either may acceptable.

Nagoyankee has said specifically that じゃない and ではありません are the typical pairings. I was taught じゃありません in school many years ago, but I have never a single time ever heard it said by a Japanese person. I lived in Kanagawa and went to school in Tokyo, for what it's worth.