Viability and fitness are often treated as interchangeable concepts, but APS distinguishes them because they address different explanatory questions.
Viability concerns whether organised persistence can be maintained under present conditions. A living system remains viable when it successfully sustains the organisation required for continued existence despite internal fluctuations and environmental challenges.
Fitness concerns whether such persistence contributes to continuity across generations. It therefore addresses the historical continuity of organised persistence rather than its immediate maintenance.
This distinction reveals an important asymmetry. Viability is explanatorily prior to fitness. Living systems must first remain viable before continuity across generations becomes possible. Fitness therefore presupposes organised persistence rather than explaining its emergence.
APS consequently treats viability and fitness as complementary temporal dimensions of the same underlying phenomenon. Viability concerns the maintenance of continuity in the present, while fitness concerns the continuity of such persistence through evolutionary time.