At the time, he thought that schizophrenia would break up into four basic groups, based on positive/negative affect (does an episode have the person doing extra activity or withdrawing) and, I think, whether or not the person has hallucinations.
I haven't really kept in touch with the literature to see how his 4-way prediction went, but I have never seen anything to counter the idea that schizophrenia is more than a single disease. And, of course, classification of disease is a key element of treating it, so if schizophrenia is not being properly classified...