1. After te-form of verb + wa
ここでタバコを吸ってはいけません。
Koko de tabako o sutte wa ikemasen.
You must not smoke here.
あまりお酒を飲んではいけないよ。
Amari o-sake o nonde wa ikenai yo.
You mustn't drink too much.
2. After stem of nai-form of verb + nakereba
もう行かなければいけません。
Mou ikanakereba ikemasen.
I have to go now.
(ikemasen may be replaced by narimasen)
3. After dictionary form of verb + to, followed by kara
雨が降るといけないから傘を持って行った方がいいですよ。
Ame ga furu to ikenai kara kasa o motte itta hou ga ii desu yo.
It's better to take an umbrella with you because it'll be bad if it rains. (You had better take an umbrella in case it rains)
4. Used as adjective
それのどこがいけないのですか。
Sore no doko ga ikenai no desu ka.
What's wrong with it?
