In logic, there are usually four fundamental laws: the Law of Identity, the Law of Non-Contradiction, the Law of the Excluded Middle, and the Law of Sufficient Reason. Mastering these can help us identify common logical errors and avoid being misled by sophistry.

First, the Law of Identity. In the same line of thinking or discussion, the meaning of a concept must remain consistent and cannot change midway. For example, if you are discussing the fruit "apple," you cannot suddenly switch to "Apple iPhone" during the argument, or it would be a fallacy of equivocation, undermining the premise of the discussion.

Second, the Law of Non-Contradiction. Under the same conditions and at the same time, two contradictory propositions cannot both be true. For instance, the statements "This year, I will not accept gifts during festivals" and "I will accept gifts only from certain people" cannot both be true at the same time; either you accept gifts or you do not, otherwise it is a contradiction.

Third, the Law of the Excluded Middle. In the same line of reasoning, two contradictory propositions cannot both be false; one must be true. That is, for a clearly defined question of right and wrong, a judgment must be made between "yes" and "no," and you cannot deny both.

Fourth, the Law of Sufficient Reason. In thinking and reasoning, a judgment is considered true only if there are sufficient reasons or grounds. Correct reasoning cannot be made out of thin air; it requires facts, evidence, or logical support. For example, deciding to take an umbrella when going out is justified if the weather forecast issued a heavy rain warning and it is already raining outside—these are sufficient reasons.

In summary, these four laws require: concepts to remain consistent, arguments to be free of self-contradiction, judgments to be clear, and conclusions to be supported by reasons. They form the basic rules of rational thinking.