Distinguishability, identifiability, and distinctability concepts lie at the heart of kinetic analysis despite the fact that they have not been described in relation to photokinetic investigation. The three concepts represent the issue of degeneracy of the kinetic solution. This chapter gives their definitions and, more importantly, demonstrates that a kinetic analysis of any photoreaction cannot be considered complete until these three concepts are fully addressed and the issues they may pose are consistently resolved. They should naturally represent the tripod pillar of a full and consistent kinetic analysis. Not addressing any of them exposes the kinetic analysis, results, and conclusions to serious mistakes, misinterpretation, and/or invalidation.