However, there are problems with this interpretation. By the time of his death he had written 10s of thousands of words. He says: those who are good at discussing antiquity must demonstrate The validity of what they say in terms of modern times; Those who are good at discussing heaven must show proofs from the human world. In discussions of all kinds, men value what is in accord with the facts and what can be proved to be valid. Hence if a man sits on his mat propounding some theory, He should be able to stand right up and put it into practice, and show that it can be extended over a wide area with equal validity. One may sit down and propound such a theory, but he cannot stand up and put it into practice, nor can he extend it over a wide area with any success At all. How, then, could it be anything but erroneous?