don't and can't

[Learneng]

Will you please explain when to use either of them.

Will this change the context of the sentence: I don't understand.....I can't understand.

[luke]

Hi Learneng,

Whilst can is a modal auxiliary verb (MDV), do is not. Thus the effects are quite different. MDV's are used to add extra meaning to the main verb, whilst don't just negates it.

So to answer your question;

I don't understand = At this time, there is no point of understanding achieved. It is likely to be a temporary thing
I can't understand = Suggests that after several attempts of trying, you still don't have the ability to understand