Theory of the Internal Space

It is postulated that fermions with identical space-time properties have to obey the exclusion principle unless they differ dynamically in their interaction with other particles. This postulate is formulated within the framework of a theory of the internal degrees of freedom. When all possible Yukawa-type couplings are examined, this postulate together with some other specification singles out the $\phi ·\tau$ interaction between pion and nucleon. Finally, when applied to electric interactions it requires the displacement of the nucleon center of charge.