I just read this lesson on imabi and i'm confused.

"To make a polite negative phrase, you have two options. You can simply add です
to ～ない. When you do this, you aren't actually saying "is" again. In this case,
です's meaning is just showing politeness. Or, you can use ～｛では・じゃ｝ありません. If you
remember from Lesson 8 that だ comes from である and that it will be important to
know this later on, the time is now. Polite conjugations using it are "more
polite" than just using です. So, they are best used with people whom you should
show more respect."
CC BY-SA 3.0
2015-07-26T01:52:16.433
25938
2015-07-26T03:03:09.777
10726
question
word-choice
This is pretty long, do you say this fully or is it one or the other? Also what does it mean? では・じゃ｝ありません
It means you can either use `ではありません` or `じゃありません` to express a negative
polite phrase.

So, `私は医者ではありません` and `私は医者じゃありません` are both fine.
CC BY-SA 3.0
2015-07-26T02:21:42.630
25940
2015-07-26T02:21:42.630
10045
25938
answer
You can make a polite negative version of a noun or na-adj by either adding
「です」 to 「ない」 (making 「ないです」) or saying 「ではありません / じゃありません」.

Examples:  
「静かではありません。」  
「静かじゃありません。」  
「静かじゃないです。」
CC BY-SA 3.0
2015-07-26T03:03:09.777
25943
2015-07-26T03:03:09.777
25938
answer