A case of double negative?

Question

Quite often I would come across conversations similar to the one below:

"Is it a difficult test?"

"Not for you it isn't."

So it's commonplace to hear constructions such as "Not for you it isn't" and "Not to me it doesn't" etc. But from my standpoint it seems like a case of double negative, as there are more than one negative element/form involved. Should I rephrase it to "For you it isn't" ? Or is it that it has become idiomatic and removing one negative element would sound clumsy in comparison?

Many thanks in advance.

Answer 1

"Is it a difficult test?"

"Not for you it isn't."

"For you it isn't." This is fine and most of us would understand what you mean, but it could mean the test isn't difficult for most people.

Not for you it isn't."

This means that the test may well be difficult for other students, but for you, (evidentially smart 'you'), it should be no problem.

Answer 2

Grammatically, you are correct. The construction is wrong. It is an informal, colloquial way of speaking. It sounds okay in conversation, but don't write it.