  Wright did not elaborate upon the difference between direct and indirect verification in actual practice. He had much more to say about differences in method between science and philosophy. He believed that all branches of knowledge had to follow the method of verification belonging to science. The “philosophy of method” is incomplete, however, in that it cannot say what constitutes verification in all the departments of knowledge. Because there is no “complete inventory of our primary sources of knowledge,” there can be disagreement as to what constitutes a legitimate appeal to observation or what is a real verification (PD 45). Platonists or rationalists claim verification for their theories because they have made an observation of what reason reveals to them. In fact, they have made an induction from rational introspection (PD 46). The positivists' claim, which Wright endorsed, is simply that “verification by reason settles nothing” and that only data from sensible experience are reliable enough to admit ideas into the range of what is held to be true.