It is often difficult to explain the characteristics of things unilaterally. According to the similarities and differences of shapes, properties, causes and functions of things, things can be divided into several categories, and then explained one by one according to the categories. This interpretation technique is called classification. Classification is an important way to explain complex things clearly. Sometimes it is necessary to explain the characteristics and essence of things from several aspects, which also belongs to classification. For example:

1. The books in the library are classified by country, China and foreign countries. There are times, classical and modern. There are also points by nature, such as science and technology, literature and political economy.

2. According to China Library Classification, library books are divided into five categories, namely, Marxism-Leninism, Mao Zedong Thought, philosophy, social science, natural science and comprehensive books, and 22 basic categories.