1. Different explanations: grades are differentiated according to different quality, degree and status, and classes are social groups in different positions in a certain social and economic structure.
2. Different criteria for division: the grades are divided according to the size of power, including the three grades before the French Revolution, and the classes are divided according to the different status and the amount of property occupied, including the peasant class, the working class and the bourgeoisie.
3. The scope of existence is different: there is a hierarchy in feudal society and slave society, and there is a class in private ownership society.