What is the difference between ～してる and ～している?


When do you omit the い? Is it ungrammatical to use してる?




してる is simply a colloquial contracted form of して **い** る, similarly one has
してない contracted from して **い** ない. It is very common in spoken language, but
ungrammatical in "proper" (school) grammar.

This contraction is maybe similar to contractions such as

  * _she had/would → she'd_
  * _it is → it's_
  * _I have → I've_.




してる is simply a colloquial contracted form of して **い** る, similarly one has
してない contracted from して **い** ない. It is very common in spoken language, but
ungrammatical in "proper" (school) grammar.

This contraction is maybe similar to contractions such as

  * _she had/would → she'd_
  * _it is → it's_
  * _I have → I've_.

