The subject of research is the theoretical and methodological foundations of the dialectic of contradictions in the development of the economic system and the classification of economic systems in the dynamics of their development. The aim of the study is quantitative and qualitative changes in the process of forming the main components of economic system development under the influence of external factors. Research methods. The article uses general and special methods of research of economic processes, analysis of economic systems and synthesis of processes aimed at forming components of economic system development. Results of work. As a result of writing the article, it was found that quantitative changes in the economic system are an increase or decrease in components or a decrease in their numerical values, which at certain stages of development lead to a qualitative leap. Structural changes in the economic system are changes in the proportions of components, which do not necessarily have to be accompanied by an increase or decrease in their number. On the contrary, the number of components may remain the same, but structural changes may lead to a qualitative leap. Thus, the conclusion that both quantitative and structural changes play a causal role in the qualitative relation to economic systems can be formulated as a threat to the security of their development. After all, according to the dialectic of the driving forces of any system, there are contradictions, and change cannot be only where there are no contradictions, we can say that external and internal contradictions are an integral part of economic systems and a threat to their security. Field of application of results. Economics and management of the national economy at the macroeconomic and microeconomic levels, enterprise management, management, strategic management. Conclusions. As a result of the study, taking into account many additional factors and features of the main components of sustainable development of the economic system, we can conclude that the basis of the economic system is the production subsystem, represented primarily by tangible and intangible industries. The core of the production subsystem are areas of specialization that determine the economic structure, external and internal relations of the economic system, the main factor – the qualifications of workers whose products are intended for export to other regions and countries (government order). The level of security of this subsystem of the economy is much higher, because the products and services of these enterprises are always in stable demand in the market. However, deep disparities in the level of development of industries and enterprises of various forms of ownership are a serious obstacle to the formation of progressive market structures and are the cause of bankruptcy of many enterprises. The social subsystem and the spiritual sphere perform the most important economic and social function – the expanded reproduction of the population. In particular, the tasks of the social subsystem include: ensuring normal living conditions of the population; education and training of the younger generation; prevention and protection of public health; social protection of the population.