I’ve previously expressed my preference for making a distinction in usage of the sort that Richard describes, so I trust I won’t be taken for a hidebound reactionary if I point out that writers of usage advice sometimes have to be descriptivists about prescriptivism, so to speak. People read usage manuals because, among other reasons, they don’t want their writing to contain what will be seen as errors. A writer of usage advice might feel that there is nothing wrong with “alright”, but if he is scrupulous he will have to warn his readers that there are still significant numbers of people who consider it an error, and that the teacher, editor, or potential employer that the reader might be writing for (or to) could be one of them.
I have no problem with a usage manual that explains the issue and points out that some people will, regardless of facts and logic, still consider the usage an error. Is there such a usage manual available? Why yes, there is. Here’ s hint: it is not by Bryan Garner.
A usage manual has more than one function. Yes, advising how to avoid the appearance of error (as contrasted with actual error) is high on the list. But people also use these things to judge others and to defend their judgments of others. Give these people a usage manual chock-full-o-facts (lets, hypothetically, call this book “MWDEU") and they will be encouraged to think about the subject rationally; at least they won’t be given ammunition to use against others.