-기(가/에)

-기(가/에) 

To be easy to + V 

-기 쉽다

To be difficult to + V

-기 어렵다

"Verb stem + 기" is a noun form, therefore in principle, there has to be a marker after it, but in the forms above, the marker is dropped.

Which markers were dropped?

It depends on the context but it can be either originally -기에 쉽다/어렵다 or originally -기가 쉽다/어렵다.

-기에 쉽다/어렵다

When you use the marker -에 it means that something is easy/difficult FOR + V-ing.

-기가 쉽다/어렵다

When you use the marker -가, it means that "DOING something" is easy/difficult.

Example #1

제 이름은 발은하기(가) 어려워요.

My name is difficult to pronounce.

Example #2

이건 만들기(가) 어려워요.

This is difficult to make.

Example #3

이건 어린이가 사용하기(에) 어려워요.

Using this is difficult for a child.

In this example, the subject of the verb is 사용하다 is 어린이 and 어린이 is followed by 가, the subject marker, it sounds rather repetitive to use -가 again, so in this kind of sentence, people tend to use -에 instead of -가 before 쉬워요/어려워요.

Example #4

사용하기가 쉬워요.

It's easy to use.

사용하기에 쉬워요.

Using it is easy.

In all the above sentences, you can drop -가 or -에.

Other words can also be used with V + -기(가/에)

Example

-기가 편리하다/-기(에) 편리하다

to be convenient to + V / to be convenient for + V-ing

-기(가) 좋다/-기(에) 좋다

to be good to + V / to be good for + V-ing

-기(가) 불편하다/-기(에) 불편하다

to be inconvenient to + V / to be inconvenient for + V-inf