There are contradictions between objective things, which do not conform to formal logic. Therefore, dialectical logic negates the rules of formal logic and makes the sentences contain contradictions in order to conform to the characteristics of objective things.
Definition: Formal logic is the rules of rational relations between sentences that do not contain contradictions. Dialectical logic is the rules of rational relations that contains contradictions between sentences.
The objective world is composed of Wu, Shi, Dao, Li and relations. Wu is material, Shi is event, the movement and change of substances and relations. Li is Plato's idea, the commonness of material, and Dao is the law, the commonness of events and relations.[2] Compared with formal logic, dialectical logic is closer to Dao. In the subjective world there are Xin, Xing, Qing, Yi and thought products. Xin is thought, Xing is nature, interests and needs, Qing is mood, emotion and vision, Yi is manner, will and decision. Formal logic is not law, it is rules, and a rule is a decision.
4. Dialectical Logic
4.1 Dialectical Logic Comes from Rethink
There are commonalities between objective concrete things. In language, commonalities can be expressed in terms of concepts. For example, the white of a white horse's fur and the white of the limestone particles are considered the same thing, and we stipulate that the white as a concept must conform to the law of identity.
The objective and real things are very complex, and when making logical rules, people could only pay attention to some attributes of the objective things and ignore others. After the rules of formal logic were formulated, problems were found in use. In order to solve these problems, dialectical logic emerged. There is no absolutely pure white in the world, at first we feel that the white of the white horse is the same as the white of the limestone, and later the difference between them may be slowly found. Another example is that all water can extinguish fire, but some water can be drunk and some water cannot be drunk. From the property of fire extinguishing, pure water and rainwater are the same, from the drinkable property are not the same. According to formal logic, water as a concept should be the same everywhere, but dialectical logic holds that the concept contains differences. People's understanding of objective things has a continuous developing process.
A piece of paper has two sides, I set the top A and the bottom minus A. If he top plane can be extended indefinitely, every part of it is A. But the top and bottom sides of the Mobius strip are connected, so top can be equal to bottom, so A can be equal to minus A. And the inside of a Klein bottle can equal the outside. At the poles of the Earth, south can equal north. You can step into the same river twice, at the same time you can't step into the same river twice.
The initial understanding of things conforms to the law of identity of formal logic, and the in-depth understanding of things produces difference, which conforms to dialectical logic. From this point of view, dialectical logic is more in line with objective reality. But dialectical logic can not be used for logical reasoning, it does not meet the needs of people. Therefore, the value of formal logic is greater, and this value makes formal logic have great vitality.