Although I definitely cringe when I hear people use "they" instead of the more "correct" "he or she," I recognize that there is probably no such thing as a "static" language.That is the consensus among grammarians who see language as a static system
For some background, an excellent course on language (which I purchased and absorbed) and how language changes over time is the one sold by The Teaching Company entitled "History of the English Language," by Professor Seth Lerer at Stanford (bio here:)
http://english.stanford.edu/bio.php?name_id=76
Here's an advertisement for the course:
http://www.teach12.com/ttcx/coursedescl ... rofessor80
(I hope posting these links doesn't break some Quatloos rule; I have no financial interest in Professor Lerer's work or in The Teaching Company - it's just a great course in my opinion).
Professor Lerer is very enthusiastic about his subject, and his lecture style is top-notch in my opinion. Really good stuff.
I also cringe when I hear what I think linguists call may call "idiolectic vowel shift" - as evidenced by the tendency of some Americans to pronounce (for example) the following sentence: "I have a good job and I'm making big bucks" as "I have a good job and I'm making big BOX." -- i.e., the tendency to shift the "u" in "bucks" to something like an "ah" sound, as the "o" in "box." Lots of educated people do this. I think it's done in an effort to sound "sophisticated" except that the people who do it may not even realize that they're doing it (pronounced "bucks" as though it's "box", for example). Although it sounds grating on my ears, it's just a normal part of the development of language.
If this tendency becomes widespread, so that the pattern is followed by a large sub-group of the population, then the practice presumably ceases being called "idiolectic vowel shift" and becomes "dialectic vowel shift." And enough vowel shifts over time, with enough different vowels, might result in something like the Great Vowel Shift that occurred in English:
http://en.wikipedia.org/wiki/Great_Vowel_Shift
Language constantly changes, sometimes slowly, sometimes quickly.
Anyway, Professor Lerer is great.