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Usually といけない follows ない形 of 辞書形. For example,

  * 寝る前に、歯を磨かないといけない。I have to brush my teeth before sleeping.
  * 明日までに宿題を出さないといけない。I have to hand in my homework by tomorrow.

Today, I read a new grammar 辞書形＋といけない. I really don't know what this grammar
mean. For example,

  * 風邪を引くといけないから、暖かい服を着たほうがいい。
  * 子供が寂しがるといけないと思って、おもちゃで遊ばせておきました。
  * 子供に言い過ぎるといけないと思うが、すぐ口を出してしまう。

The book also provides other but similar meanings for each sentence above as
follows.

  * ～引いてはから～ is equal to ～引くといけないから～
  * ～寂しがってはと思って～ is equal to ～寂しがるといけないと思って～
  * ～言い過ぎてはと思うが～ is equal to ～言い過ぎるといけないと思うが～

Any comments and suggestion are appreciated.
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2016-04-05T15:16:34.727
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2016-04-05T17:07:17.653
2016-04-05T15:21:25.040
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question
grammar
What does 辞書形＋といけない mean?
I think that what is important to see here is that the と here is the
conditional-と.

>   * 歯を磨かないと…if you don't brush your teeth
>   * 風邪を引くと…if you catch a cold
>

Next step is to understand the いけない part. You can see it as _won't go (well)_
in the meaning of _not good_.

>   * 歯を磨かないといけない…if you don't brush your teeth, that'll be not good. (Hence
> the meaning of: you **must** brush your teeth.)
>   * 風邪を引くといけないから、暖かい服を着たほうがいい。…because if you catch a cold it will be _no
> good_ , you'd better wear a warm piece of clothing. (Hence, you should wear
> a warm piece of clothing because you don't want to end up catching a cold.)
>

* * *

Here ては is a shortened version of てはだめだ・てはいけない・てはならない. Again, ては indicates
conditional.

So 引いては~から ≒ 引いてはいけない ≒ 引くといけない
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2016-04-05T15:48:20.627
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2016-04-05T17:07:17.653
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answer