In the same way, it can also be proved that subjective things obey the law of exclusion of middle and the law of non-contradiction. In the past, everyone believed that the law of identity, the law of exclusion of middle and the law of non-contradiction were objective laws. Through the above argument, it can be found that they are originally rules of the subjective world, and methods for dealing with logical structures in the subjective world, rather than methods for dealing with real things in the objective world.

Theorem: The law of identity, the law of exclusion of middle and The law of non-contradiction are the rules of subjective things, and objective things do not abide by the law of identity, the law of exclusion of middle and the law of non-contradiction.

3.2 Cognition Process from Simple to Complex

Objective things are too complex to follow formal logic. If we want to make objective things obey formal logic, we must simplify objective things. For example, each game has its own rules, chess stipulates that pawns can only move one square at a time, only forward, not backward, the chariots can only go straight, the phase can only go diagonal, and so on. These rules are different from objective reality, where chariots can't just go straight. But to play the game must abide by such rules, otherwise it is not fun, can not meet the needs of people.

Formal logic is the rules of rational thought, rules that are simple and useful but unreal, like the rules of chess. The understanding of any objective thing requires a process from simple to complex. The rules of formal logic, including the law of identity, the law of exclusion of middle and the law of non-contradiction, are all artificial logical structures. There is no such logical structure in the objective world, and the purpose of constructing such logical structure is to simplify thinking. The purpose of simplification is to make the sentences do not contain contradictions, and make it convenient for thinking processing, calculation and prediction.

For example, I want to know if the Chaobai River will flood this year. I shall first investigate the flooding information of Chaobai River in previous years and then conduct a statistical analysis. But the river is concrete and complex and changes every year, including the height and strength of river levees, the amount of silt at the bottom of the river, and the amount of aquatic plants. It even changes every day, you can't step into the same river twice. What should I do if I can't use the hydrological data from the last ten years to predict what the river will do this year? We must simplify and assume that all conditions remain the same, that is, the Chaobai River of the past ten years is equal to the Chaobai River of today. Under this premise, the possibility of flood disaster in this year's flood season is predicted, and a preliminary conclusion is obtained. Then, when there is time and conditions, it will be further studied step by step according to the height and strength of the embankment, the amount of silt at the bottom of the river, the amount of aquatic plants and other specific conditions. These in-depth studies should lead to more accurate and true conclusions, but the situation is often too complex to bear fruit. That's when that preliminary conclusion becomes very useful and important. I use the law of identity of formal logic when simplifying and abstracting, and I think this year's Chaobai River is the same river as that of previous years. This is a hypothesis that is simple and useful but not objectively true. The effect of this hypothesis is to reduce a real concrete thing to an abstract logical construction. I am studying a river that has been simplified, and I am dealing with this logical construction, the dealing is a game of thought within the subjective world.