Korean From Zero! – Lesson 16 – Not being able to do
16-15. Contracted versions of 지 못하다 and 지 않다 There are shorter versions that are commonly used for ~지 못하다 (unable to) and ~지 않다 (won’t, don’t) forms. The short versions are 못 and 안. They are added directly in front of the 다 form of the verb. Then all you do is treat it as a NEW verb and follow all the patterns and rules you already know. Simple!
Even though in the prior section we taught distinct differences between ㄹ 수 없다 (can not) and 뭇 + verb (unable) actual usage if among Koreans doesn’t follow such clear lines. For example, it’s more common to just say 못 해요 to say you can’t do something than 할 수 없어요.