In this paper the author distinguishes the substantial, logical and semantic differences between laws and rules. Laws are discovered by man and independent of man’s will. Laws play their own roles by themselves and it is impossible that they are disobeyed. Rules are worked out by man and play their own roles by following them. From the point of view of grammar, laws are declarative sentences and rules are imperative sentences. Man can follow rules or can not follow rules. The paper has the semantic analyses of the meanings of the sentence that man acts according to laws. It holds that man acts according to rules. Rule?following that is a basic way for man to act is closely related to human nature, according to which man can regarded as an economic one or as a social one, and rationality, maximized rationality or adaptable rationality.
