Biological explanation becomes unstable when Agency, Cognition, and Sentience are treated as interchangeable. In APS, they refer to different biological or experiential attributions, and evidence for one does not by itself establish the others.
Agency is viability-oriented activity through which living organisation sustains the conditions of its persistence. It is therefore fundamental to life, but Agency alone does not establish Cognition. Biological Evaluation, Significance, and Integration may organise activity in increasingly flexible ways without necessarily crossing the cognitive threshold.
Cognition is a further attribution. Biological agency becomes cognitive when integrated biological significance modulates activity across a temporal field of viability-relevant possibilities in ways not exhausted by immediate or fixed regulation. Cognition therefore cannot be inferred merely from responsiveness, regulation, evaluation, learning-like change, or other capacities that may also admit an adequate non-cognitive explanation.
Sentience, by contrast, concerns subjective experience. Neither Agency nor Cognition, as APS defines them, is sufficient evidence that a system experiences, feels, or is aware. Cognitive organisation may therefore be investigated without assuming Sentience, just as viability-oriented Agency may be investigated without assuming Cognition.
The distinctions are consequently both conceptual and evidential. Evidence for Agency does not automatically establish Cognition, and evidence for Cognition does not automatically establish Sentience. Keeping these claims separate allows biological organisation, cognitive activity, and subjective experience to be investigated without importing properties from one into another.
Key Point. Agency does not entail Cognition, and Cognition does not entail Sentience. Each attribution requires evidence appropriate to the phenomenon being explained.