Scattering and Bound StatesMankind's unified understanding of scattering and bound states has been very brief. It is therefore not unusual to expect that separate theoretical models be developed for scattering and for bound states. The successes and limitations of Feynman diagrams are well known. The covariant harmonic oscillator formalism takes care of Step 1. In order that both field theory and the oscillator formalism be useful for constructing a theoretical model belonging to Step 2, they should be based on the same set of physical principles.