Vygotsky believes that the use of tools makes people adapt to nature in a new way, that is, the indirect way of material production, instead of adapting to nature in a direct way like animals. The indirect experience of human beings, that is, the experience of social and cultural knowledge, is condensed in the production of human tools, which makes the law of human psychological development not restricted by the law of biological evolution, but by the law of social and historical development.

Of course, the tool itself does not belong to the psychological field, nor does it join the psychological structure. It is precisely because of this indirect "material production tool" that "spiritual production tool" appears in human psychology, that is, the unique language and symbols of human society. The similarity between production tools and language symbols is that they make indirect psychological activities produce and develop. The difference is that production tools point to the outside, causing changes in objects, and symbols point to the inside, which does not cause changes in objects, but affects people's behavior. Controlling nature and controlling behavior are interrelated, because people are changing their own nature while transforming nature.

Secondly, he discussed the essence of "development" and put forward his concept of cultural and historical development. Vygotsky believes that in the eyes of psychologists, development refers to psychological development. The so-called psychological development refers to: a person's psychology (from birth to adulthood) is a process of gradual transformation from low-level psychological function to high-level psychological function under the influence of environment and education.

What is the sign of the development of psychological function from low level to high level? Vygotsky can be summarized into four aspects: 1, a random function of psychological activities; 2. Abstraction of psychological activities-generalization function; In other words, various functions are advanced by the participation of thinking (mainly abstract logical thinking); 3. The relationship between various psychological functions is constantly changing and combining, forming an indirect psychological structure mediated by symbols or words; 4. Personalization of psychological activities.

What are the reasons for the development of psychological function from low level to high level? Vygotsky emphasized three points: first, it originated from the development of social culture-history and was restricted by social laws. Secondly, from the perspective of individual development, children form various new psychological functions on the basis of low-level psychological functions by mastering the intermediary links of high-level psychological functions-language and symbols. Third, advanced psychological function is the result of constant internalization.

It can be seen that Vygotsky's psychological development view is closely related to his cultural-historical development view. He emphasized that the advanced function of psychological development is the product of interpersonal relationship and social, cultural and historical development in the process of human material production; It is emphasized that the psychological development process is a qualitative change process, and a series of indicators are determined for this change process.