I've heard the definition of a necessary assumption, many many times. But for some reason, it doesn't click in my head 100 percent.

A necessary assumption is something that is REQUIRED for the argument to be true, meaning if this assumption is false, then the argument CANNOT be valid. The conclusion WILL not follow given the evidence.

But does this mean that no matter what premises you add to the current argument, the conclusion will not follow - or just that the GIVEN, limited evidence cannot be used to come to the conclusion? Sometimes I've seen an approach where people look for situations where the conclusion does follow, despite denying the assumption - that's how you can tell it's an incorrect choice. But this does not make intuitive sense to me because I feel like you can always come up with premises where they can make the conclusion follow.

I hope I'm making sense..