This article is exactly what Persig is talking about. In it, a mother, Kim O'Connell, recounts her experience with her son Declan's extended periods of complete silence, which she discovered has a name: Selective Mutism.Through multiplication upon multiplication of facts, information, theories and hypotheses, it is science itself that is leading mankind from single absolute truths to multiple, indeterminate, relative ones.
So science has added another category, that's what science is all about. It's a process that began with Aristotle. It's called classification. Selective Mutism is unique, requiring unique handling, unique treatment and possibly unique drugs--multiplication of facts, etc., leading from single absolute truths (root causes, if you will) to multiple, indeterminate, relative ones. The child's behavior, in other words, is meaningless. These are just symptoms of a disease that he's come by at random.