A number of particle properties stem from the use of γ 0 as adjunctator (Bargmann-Pauli) in the Dirac theory (spin alignment, Dirac current, etc.). The early motivations for accepting γ 0 as adjunctator were representation-dependent, mildly bearing relation to the actual conditions forcing γ 0 as adjunctator. Representation-independent approaches to the physical predictions of the Dirac equation are somewhat new, here presented as being the reasons for γ 0 as adjunctator of the Dirac theory, together with the essential role of the latter in the physical aspects of the theory.