Reductionism is often understood as the view that explaining a system requires analysing its smallest components and the physical laws governing them. APS accepts that living systems are materially constituted in this way but rejects the assumption that explanation begins at that level.
Biological explanation concerns how systems sustain themselves as organised, viable entities over time. Components such as genes and molecules contribute to this activity, but their biological significance arises only within the organisation they help maintain. Outside that context, they remain physically real but are not yet biologically explanatory.
APS therefore distinguishes material constitution from explanatory priority. What a system is made of does not by itself determine how it must be explained. Explanation begins where biological intelligibility begins: with viability-oriented, constraint-closed organisation.
Reductionism is thus not rejected but delimited. It captures the material basis of living systems while leaving open the organisational conditions that make biological phenomena possible.