Sometimes, I forget to use the proper form when an adverb is required. Or sometimes it simply doesn't appear to me one is required, unless I actually consider the grammar of my sentence. I suppose that's mostly because in my native language (German), there is no morphological difference between an adverb and an adjective.
This led me to wonder:
Is this distinction in English merely an idiosyncrasy or can I really semantically convey something other than intended, if I omit the suffix by mistake?