Prescriptive Grammar does more harm than good

(Apologies for the shortness of the argument presented here. At the time of this writing there is thirty minutes left on the clock. No excuses, just an explanation. Many apologies.) My opponent starts off her argument by asserting that prescriptive grammar is unnecessary because all that is needed for communication between two individuals is a "shared grammar." But my opponent seems to be missing the entire point of grammar. Grammar is a set of rules that sets a standard for a great population so that it becomes easier for that population to communicate. For example, in the sentence "Bob opened the crate of apples that had a birthday last month," it is clear, though not at first, that it is Bob that had a birthday, not the crate of apples. But it's confusing. Prescriptive grammar tries to combat ambiguities such as these. Grammarians would say that sentence contains an "ambiguous that." They'd say the sentence is better revised, "Bob, who had a birthday last month, opened the crate of apples." So, while it is hard to conceive why someone would say "butter is than better margarine," it is clear that prescriptive grammar is necessary to promote clearer communication. My opponent then goes on to assert that a generation will fill in the grammatical blanks of the previous generation and that is therefore unnecessary to have any authority on grammar. Again my opponent seems to be missing the entire point of grammar. Let us take an example somewhat removed from grammar: diction. Is there anything inherently wrong with someone using a word differently from everyone else? No, not really. Those listening can always ask for clarification, and as long as there is some common ground between the speaker and listeners they will eventually come to understand one other. But it's awful annoying. We have supreme sources to clarify what is and what is not correct to make thing easier. Same thing with grammar. My opponent then goes on to say that prescriptive grammar changes with time. But I fail to see how this is much of a problem. A lot of grammar is inherent. For example, in the sentence "The person who killed your father is I," it is logical to say 'I,' because "is" is a linking verb which tells the listener that this one thing equals this thing. So, the subjective case makes sense. To my knowledge, this rule has not changed since its conception. It makes complete and logical sense. But other rules do change. For example, it used to be acceptable to use the relative pronoun "which" when referring to people, as in "our father which art in heaven." But with time, grammarians realized that to avoid ambiguities it was best to reserve the relative pronoun "who" (with the occasional exceptions for "that") when describing people. So, grammar does change, and there is an objective component to it... so what? With more understanding, science changes. Is this somehow a problem for science as well? In closing, my opponent attempts to illustrate harm caused by prescriptive grammar, saying that those who have not been trained in prescriptive grammar are unfairly punished. You know, I was on a music review website the other day (http://thepunksite.com...), and it was clear that the reviewers did not understand even basic grammar. They misused semicolons, misused vocabulary ("then/than" and "it/it's"), and just had horrendous style. And I immediately closed the website and went to the Rolling Stone. My opponent would argue that I unfairly treated ThePunkSite.com. But here's the thing: whether she likes it or not, grammar *is* a good indicator of how educated someone is. It's a way of showing the reader you're intelligent, at least in the academic sense. And that's not to say that one should *always* follow the rules. In the above paragraphs, along with the unintentional typos, I've made many intentional errors. Instead of calling misuse of vocabulary "awfully annoying," for example, I used the incorrect "awful annoying" to more fully express my disgust. But here's another thing: you can only know how to break the rules if you know the rules beforehand. And once you do know the rules, you're free to express yourself in ways you never could have before. You'll notice, for example, that the vast majority of the literary Gods had great control of prescriptive grammar. Might I suggest that this is not a coincidence.