Two Sides of Spin Concept
The notion of the spin is shown to have two constituents, as exemplified by the spin of the electron. The first one is related to the form of the wave equation and determines the fermion or boson particle type. This implies the spin taking strictly half-integer or integer number. The second side of spin manifestation is related to the physical nature of the spin of the electron (and the corresponding magnetic moment) in the interaction resulting in nonuniform motion. It is shown that in this manifestation spin is no more fixed constant.