In the phenomenological approach, the problem of the possibility of applying the additivity principle to the calculation of physical quantities or characteristics of multicomponent solid metal solutions, including high-entropy ones, is analyzed. These values and characteristics include the lattice parameter and the Debye temperature, since they can be considered indirectly through the radius and mass of an atom as their own, rather than collective, characteristics of individual components, such as, for example, the magnetic moment of an atom, magnetization, heat capacity. It is proposed to consider the relative change in resistance when measuring the thermal coefficient of resistance or the strain coefficient as conditionally individual characteristics of individual components. At the same time, applying the principle of additivity to collective quantities or characteristics (melting temperature, Fermi energy, mean free path of electrons) can give very approximate values.