For me a grammar is a sort of abstract device for parsing and generating acceptable sentences in a given language.
I think this is how I understand grammar too.
With breaking a rule because you never exactly knew what the rule was I meant: in many publications, newspapers, magazines, critics and articles I notice that they are more and more written by people who never learned to properly use this sort of abstract device for parsing and generating acceptable sentences in a given language. So they (sentences) are not acceptable but is seems to be such a general phenomenen.
If I may, I think that your understanding grammar does differ a great deal from how zmj and I understand it. For me, this abstract device for parsing and generating acceptable sentences is acquired by children, almost automatically and largely unconsciously. By the time children learn to read, they already have a mastery of most of the grammar of their language. So when you say that there are adults who don't understand how to use this abstract device for parsing and generating acceptable sentences, in other words they don't know the grammar of their native language, I'm very skeptical.
A real example might help.
