There's where we part company

Not bad parting company as long as we have a conversation.

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.

There is a difference between breaking a rule for an obvious purpose or breaking a rule because you never exactly knew what the rule was.

I meant when someone writes well, thus handling this device for parsing and generating acceptable sentences in a given language well, he/she may want to take "liberties" for expressive or aesthetic or whatever reasons which I called "obvious purpose" (which apperently wasn't very clear and obvious).
To a good reader these free movements in writing are obvious, I mean logic, natural and enjoyable.

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.

Question: do you still think it is important that children learn grammar well. We are not born with this understanding.
We really have to learn it. All of us. ( olly :~) )