In APS, multiple realization does not imply that any material arrangement can perform any biological function. Biological organisation remains constrained by the requirements of viability-oriented persistence.
What can be multiply realised are not isolated outputs, behaviours, or functions considered in abstraction, but organisational roles within systems that successfully maintain continuity across time. Similar viability-oriented roles may therefore be realised through different material, developmental, ecological, or evolutionary pathways, provided those pathways preserve the organisational relations required for persistence.
For this reason, APS treats multiple realization as constrained rather than unrestricted. Different structures, mechanisms, or processes may support comparable biological roles only where they maintain the conditions necessary for viability, regulation, development, reproduction, adaptation, or continuity more generally.
This reframes the concept biologically. The central question is not simply whether different mechanisms can produce the same effect, but whether different forms of organisation can sustain comparable patterns of viable persistence.
Key Point: In APS, multiple realization concerns the possibility that different organisational pathways may sustain similar continuity-preserving roles, provided the requirements of viability-oriented persistence remain satisfied.