s. The concept may be the name of commonness of things or the name of a set of things, the standard of classification is the commonness. The content of concept is the logical construct produced after abstraction of things. Different degrees of abstraction can produce different degrees of concept. For example, sparrow, bird, animal, creature, matter are all concepts, but they have different degrees of abstraction.

G.C.Lichtenberg, Professor of physics at Gottingen University said, "Mother Nature does not create genera and species, she creates individuals."[5] Therefore, concept is not the simulation of objective things, but the innovation of logical construct. The method of innovation is abstraction. For example, there are many kinds of birds, there are migratory birds and resident birds, there are carnivores and omnivores, and there are many differences in size, call, color and so on. The concept of "bird" ignores all these differences, focusing only on the fact that they have wings, no teeth, etc., and then we make the logical construct of "bird". The concept does not exist in the objective world. There are sparrows and eagles, but no individual animal is named bird. The objective world has white, red, yellow and black horses, but no horse. There is not a horse in colour both white and black, yellow and red at the same time. The concept "horse" can only exist in the human mind as a product of thought game. So Gongsun Long, an ancient Chinese thinker, said, "A white horse is not a horse."

Gongsun Long said, "A chicken has three feet." Because he added concepts of different abstract degrees together. A chicken's feet include the left foot and the right foot, which are abstracted to produce the concept of "foot". The abstract "foot" is neither left foot nor right foot, and it includes both left and right feet. It includes the feet of all chickens, big and small, of all colors, it is both one foot and countless feet. The two feet of a chicken should not add to the abstract foot of course.