The apparatus of deductive methods of reasoning developed by mathematical (symbolic) logic is usually not applied in an explicit form not only at the level of everyday reasoning, but even in such a strict science as mathematics. This, however, does not mean that the theory of deduction (including such a section as metamathematics) has a purely theoretical interest. It is widely used in the foundations of mathematics, in solving some mathematical problems, in engineering. Ideas and methods of symbolic logic became widely used in the analysis of individual fragments and components of scientific knowledge in general (the logic of scientific knowledge). However, in logic there is such a section as the theory of definition, which studies components that are present in an explicit form (or implied) in any more or less complete reasoning (both everyday and scientific), in any concept or theory.