Before discussing the Later Mohists in greater detail, let us glance at the textual explanation of the loss and recovery of the Mohist Canons. The currently accepted textual theory says the Mohists wrote two 'Canons' (I and II). Each consisted of around 80 short maxims. Since they were short, Mohists economized by writing the first half of each Canon vertically across the top of a standard sized book of bamboo strips. They wrote second half along the bottom; a key phrase at the end instructed us to read this text "in rows." The editors indexed the terse theorems of the Canon to another bamboo book called Canon Explanations. These contained longer passages including explanatory formulae, examples and arguments for the Canon's maxims. They indexed the Explanations by writing the first character of the relevant Canon to the side of the explanatory string.
We suppose that later scribes, lacking understanding of both the organization and the philosophical thrust, copied straight through each strip ignoring the "rows." Effectively, they shuffled the Canon like a deck of cards. Since Classical Chinese had no punctuation or grammatical inflection, this textual disaster (1) obscured the slogans, (2) jumbled the order and (3) shrouded the indexing principle. The scribes also shifted the indexing character into the flow of the text of the orphaned explications. Having lost the ordered link between canon and explanation, the tradition then treated the whole corpus as incoherent essays. Other common sources of textual corruption, including displaced strips of characters, mistakes in copying, scribal emending and so forth, further complicated the textual puzzle.
The philosophical sophistication and difficulty of the text,
The school's obliteration at the beginning of China's philosophical Dark Age (roughly 200 BC),
The placement in the middle of the most vociferous anti-Confucian classical text,
Medieval Confucian orthodoxy did not tackle the puzzle until the textual studies movement of the late Qing (1644-1911). Angus Graham credits Sun I Jang (1848-1908) with the insight about how to reorder and analyze the content—the instruction to 'read these horizontally.' (Sun, in turn, credits it to Bi Yuan.) Various Chinese scholars proposed reconstructions. Angus Graham's Later Mohist Logic, Ethics and Science delivered a well-argued version of the reconstructed text to Western sinologists in 1972. Many problems and obscurities remain, but Graham's reconstruction was enough to reveal a reflective, coherent and reasonably sophisticated theory of language.
The maxims do deal with central philosophical concepts and, like Chinese dictionaries, frequently consist of lists of substitution characters or a range of examples. Some slogans are metaphors on which the Explanations expand. Others are helpful ways of re-thinking and reflecting on a familiar concept. In addition to theory of language, intelligible sections of the Canon present fragments of ethics, epistemology, geometry, optics, and economics.