Difference between なくては and なくてはいけない


What's the exact difference between なくては and なくてはいけない?




# なくてはいけない

  * なくては (unless) + いけない (not good) = necessary
  * Connects to a verb to mean that you must verb

> 寝{ね} **なくてはいけない** 。  
>  _I **have to** sleep._

# なくては

  * Doesn't have いけない
  * Can imply なくてはいけない on its own, usually in the form of なく **ちゃ** : 

> 行{い}か **なくちゃ** 。  
>  _I **gotta** go._ (lit: **If I don't** go.)

  * Almost always used with a negative verb, but can also work like this: 

> 契約{けいやく}を守{まも}ってくれ **なくては困{こま}る** 。  
>  _You **must** keep to your agreement._ (lit: I'll be **troubled if you
> can't** keep to your agreement.)

  * When used with kanji （ **無{な}** くては）, doesnt usually attach _to_ a verb and usually defines _what_ can't be done: 

> この辞書{じしょ}が **無{な}くては済{す}まされない** 。  
>  _I **cannot do without** this dictionary._ ~~(it's the truth)~~




# なくてはいけない

  * なくては (unless) + いけない (not good) = necessary
  * Connects to a verb to mean that you must verb

> 寝{ね} **なくてはいけない** 。  
>  _I **have to** sleep._

# なくては

  * Doesn't have いけない
  * Can imply なくてはいけない on its own, usually in the form of なく **ちゃ** : 

> 行{い}か **なくちゃ** 。  
>  _I **gotta** go._ (lit: **If I don't** go.)

  * Almost always used with a negative verb, but can also work like this: 

> 契約{けいやく}を守{まも}ってくれ **なくては困{こま}る** 。  
>  _You **must** keep to your agreement._ (lit: I'll be **troubled if you
> can't** keep to your agreement.)

  * When used with kanji （ **無{な}** くては）, doesnt usually attach _to_ a verb and usually defines _what_ can't be done: 

> この辞書{じしょ}が **無{な}くては済{す}まされない** 。  
>  _I **cannot do without** this dictionary._ ~~(it's the truth)~~

