One chapter in the later Mohist texts, known as Xiaoqu, is probably the most important in Mohism. This were the essential rules about how words refer to things.
The Xiaoqu chapter lists five similarities and differences between statements:
(1) Sameness in being identical (two names refer to the same object, event, or situation) (versus difference in reference to two objects)..
 
(2) Sameness in being separate parts of the same unit (being part of the same whole) (versus difference in the sense of not being attached).
(3) Sameness in being together or united (versus difference in not being in the same place).
(4) Sameness in being “of a kind” (the same category of thing) (versus difference in not being of a kind).