This paper attempts to deal with a short passage found at the end of the third chapter of the Huai Nan tzu book, a compendium of learning assembled in about 120 B.c. under the patronage of the prince Liu An I first became interested in it after reading the tantalizing reference in Needham (SCC, III, 224). (It occurs to me that the preceding sentence or some variant of it is likely to occur in learned journals with a high frequency for the next 50 years at least.) My first efforts to understand the original text led me to the conclusion that it was unique in a number of ways and had points of interest that did not fully appear in the version of Maspero, 1929, 348 ff. Professors A. C. Graham and D. C. Lau both gave very generously of their time in discussions of my first draft. Professor Graham raised the question of possible Mohist influences and brought to my notice a commentary by the Ch'ing scholar Ch'ien T'ang , Huai Nan tzu t'ien wen hsün pu chu c. 1788. I did not feel able to follow Ch'ien in all he wrote, but was relieved to find that we reached the same general conclusions about what the text was saying, although Ch'ien seems to miss much that is important. While there are still some obscurities of language in what appears to be a rather corrupt text, I offer the version given here with a fair degree of conviction that it does not substantially misrepresent the intentions of the unknown author. Any errors that I have obstinately retained despite the helpful advice given to me throughout the time I was engaged on this work are, of course, my responsibility alone.