Really, there are only two schools: the prescriptivists and the descriptivists. Specializations only confound this dichotomy. For the sake of what exactly? I’m not yet so sure. All the so-called sub-fields are just attempts to take prescription out of the picture—the race to objectivity and to publish! Then, of course, you have corpus linguistics which is modernity’s fancy word for philology, except not as classy. There, I said it.