Adult native English speakers do not commit errors in usage.

<Nice example, but the teacher's reponse here strikes me as a rather elaborate attempt to avoid being labeled "prescriptive" -- a label to which the teacher seems to have a pathological abhorrence!  >

What an odd sort you are, Jim. If a teacher tries to tell things the way they are, he abhors prescriptivism. And pathological? Don't be so melodramatic, Jimmy.

<once the student gets to America maybe he can try using "ain't" himself, and see what kind of reaction he gets, and decide for himself.  " src="/emoticons/emotion-1.gif">>

Let's run it. See what folks think:

Student: Sir, should we use "ain't" if we go to America?

Teacher Jim: Tell you what, when you get to America you can try using "ain't" yourself, and see what kind of reaction you get. Then you can decide for yourself. 

Students All: ........................

<Should we ...? is a yes/no question.>

For whom? And just because you ask me a yes/no question, does it follow that I have to give a yes/no answer? Now who's being prescriptive, Jim?

<It's like asking what time it is and being given a survey of how timepieces are made in different countries.>

<Lastly, I think you may be trying to slip the word appropriate into that answer to show that considerations of appropriateness are not necessarily prescriptive.>

A rather pathetic comparison, Jim.

Nobody is trying to slip anything anywhere, Jim. You've decided upon, and been precriptive about, the meaning of the word appropriate. You've insisted that a teacher who uses that word is behaving prescriptively in all cases of that use. I do not agree with your interpretation/s.

<I think the teacher's use of appropriate implicitly means 'you should' to the student.  >

Difference?

Teacher:1 I say you should.

Teacher 2: They say you should.

....................

 

A should is a should is a should.  No student could mistake that "they" refers to an authority of some kind, so the I / they distinction is immaterial.

CJ

BTW, Jim, what does the term "Forum Guru" mean to you and how do you think most students here interpret that label?

In this last series of posts, the discussion has become too diffuse to follow.  It now seems to be going off in all directions, with no real hope of regaining focus.  I just want to point out that having an opinion is not the same as prescribing, and that the word "prescriptive" has taken on the status of a curse, both in this thread and in the field of language study in general.  I'll just have to leave it at this:  Yes, I do prescribe at times, and I do describe at times.  But in doing the one or the other I don't see myself as criminal or saint.  Get a grip, people! 

CJ

At great risk of being the next person tarred and feathered, perhaps we need to think of these pursuits - teaching and describing - like an anthropologist and a policeman. One merely notes what it happening as scientific study and the other tries to ensure the society mores and norms, as codified by laws, are followed.

The analogy breaks down because there is no one standard to decide that English usage is "legal" or not -- there is no Supreme Court, only various usage panels, and the body of literature, and so on. So the teacher/editor is in the position of trying to convey the laws as they understand them, without universal agreement on what they are.

If Faulkner writes in a way that the M-W usage panel would find non-standard, who is "right"? No one here can say. Some who have said "This is standard English" on here have been vilified on the forums as not being open to other various "legitimate" dialects.

When I make comments like "You could say it this way" or "That would be wrong" I generally mean in American business today, because "American business English" is my standard.

Unless we have a formal council on the proper use of the English language, we will simply never have agreement here on "shoulds."