Which is some gain actually: "hpd" is itself a way of paraphrasing facts, not an explanation. But it carries on its face that emptiness. The "personality" part does something else: it offers (still *not* an explanation) the provisional estimation that it is a class of disorders that probably have different dynamics (and causes) than "affective" disorders (e.g., depression) or cognitive disorders (e.g., schizophrenia).
Classification is *not* in itself science, hardly much of a beginning even, but it certainly helps not to try to find a common explanation for the rotting of peaches and the dissolution of meteors. Not knowledge, but a provisional guide to expanding knowledge. And it also makes it easier to dismiss cockamamie diagnoses such as "multiple personality disorder," which doesn't even name anything.
And I say this even knowing that *probably* the terminology will change again, and I can't predict in advance that the terminological change will be more than fashion, but neither can anyone predict in advance that it *won't* be more than fashion.
Carrol