Eugene Volokh's article Correcting Students' Usage Errors Without Making Errors of Our Own, 58 J.L.E. 533 (2008) reminds those of us who have been teaching or practicing for some time of something we probably learned early on when commenting on the writing of a student or new lawyer:  there is a difference between an actual usage error and a manner of writing that most lawyers prefer.  For example, as a new professor,  I was surprised to find that many students use "can not" rather than "cannot," when, throughout my life, English teachers had impressed upon me that only the latter was correct.  (In fact, my spell-checker is marking "can not" incorrect now!)  Nowadays I do point out errors to my students, but, more importantly, I talk to them about their audience.  Volokh uses the example of how most attorneys prefer "judgment" to "judgement."  By focusing on what trained legal readers expect, I avoid misrepresenting a spelling or usage as incorrect when it may be permissible.  But I also find that such a focus has the added benefits of making the students feel welcomed into a certain tradition of writing and keeping them more engaged.  So remember, next time you pick up your pen or pencil to edit a student or new lawyer's work, try to comment on the acceptability rather than the correctness of the writing.