Аннотация:The work is devoted to the problem of harmonization of the philosophical foundations of dynamics and thermodynamics. The laws of mechanics are reversible, which seems to contradict the condition of the increase in entropy in a closed thermodynamic system, which follows from the second law of thermodynamics: it turns out that different parts of physics interpret the concept of time differently. At the beginning of the 20th century, the problem of the contradiction between dynamics and thermodynamics attracted close attention; now interest in it has noticeably waned.The basis for solving this problem is the ontological principle of the unity of the world. The contradiction under discussion exists in our descriptions of nature, and not in nature as such: Nature is one in its essence, and cannot have logically contradictory properties. The mistake is the violation of the law of identity in the process of reasoning, leading to a “contradiction” between mechanics and thermodynamics: the 2nd law was introduced axiomatically in the construction of thermodynamics; then it was substantiated within the framework of statistical physics by Maxwell and Boltzmann based on the theory of probability; for any system there is a non-zero probability of its violation. Thus, when the 2nd beginning is reduced to dynamics, it is treated as a statistical law, and then requirements are made to it as to a dynamic law. The “contradiction” between dynamics and thermodynamics is a consequence of this illegal (for an essentially probabilistic statement) status of the 2nd principle, which imposes a ban on some dynamically possible states.