From Definition to Method

APS defines life as viability-oriented, constraint-closed organisation. Diagnosis, therefore, cannot consist in identifying traits or components. It must evaluate whether a system is actively sustaining the conditions of its own persistence.

This article provides a practical method for doing so.

The Diagnostic Question

All APS diagnosis is organised around a single question:

Does this system sustain its own viability—and how?

Everything that follows operationalises this question.

Step 1 — Identify the System as an Organised Whole

Diagnosis begins by specifying the system under investigation.

This is not a trivial step. In APS, a biological system is not defined by boundaries alone but by functional coherence—the organisation through which processes contribute to continued persistence.

For a formal definition, see What Is an Organism?.

Diagnostic focus:

  • What processes are functionally integrated?
  • What constitutes the system’s continued existence?

Step 2 — Assess Constraint Closure (Necessary Condition)

Next, determine whether the system exhibits constraint closure.

This involves identifying whether processes within the system mutually sustain one another in a closed network of dependencies.

However, this is only a threshold condition.

For clarification, see Constraint Closure — What It Does and What It Does Not Do.

Diagnostic focus:

  • Do processes contribute to maintaining the conditions that enable other processes?
  • Is the system organisationally self-sustaining, or merely assembled?

Step 3 — Apply Perturbation

Diagnosis becomes meaningful under perturbation.

A perturbation is any disruption that challenges the system’s continued viability:

  • environmental change
  • internal failure
  • resource limitation

The goal is not to destroy the system, but to reveal how it responds.

For the role of organism–environment relations in this process, see Organism–World Coupling — Why Agency Is Not Control.

Step 4 — Evaluate Organisational Response

Following perturbation, evaluate how the system responds. Three outcomes are diagnostically distinct:

  • Degradation
    The system fails to recover and moves toward breakdown

  • External Stabilisation
    The system is restored only through external intervention

  • Endogenous Reorganisation
    The system reorganises its own activity in ways that restore viable conditions

Only the third outcome demonstrates biological agency.

Step 5 — Assess the Viability Gradient (VG)

Diagnosis is not binary. Systems differ in how effectively they sustain themselves.

The Viability Gradient (VG) captures this:

  • High VG: robust, adaptive maintenance of viability
  • Low VG: fragile, easily disrupted organisation

Diagnostic focus:

  • How resilient is the system under perturbation?
  • How effectively does it restore viable conditions?

Step 6 — Assess the Normativity Gradient (NG)

Diagnosis also evaluates how the system differentiates between viable and non-viable states.

The Normativity Gradient (NG) captures the degree to which:

  • the system’s activity is oriented toward persistence
  • deviations from viability are detected and corrected

Diagnostic focus:

  • Does the system modulate its activity in response to conditions?
  • Are changes directionally oriented toward restoring viability?

Step 7 — Assess Cognitive Integration (CI)

Finally, assess the integration of regulation across the system.

The Cognitive Integration (CI) dimension distinguishes:

  • simple reactive adjustment
  • coordinated, system-wide modulation
  • integrated regulation across multiple processes and timescales

Diagnostic focus:

  • Are responses local or system-wide?
  • Does the system coordinate multiple processes in restoring viability?

Step 8 — Evaluate Across Scale

All diagnosis must be multiscale.

A system may:

  • maintain short-term stability while degrading long-term
  • exhibit local coherence but global failure

Diagnostic focus:

  • Is viability sustained across relevant timescales?
  • Are processes coordinated across spatial extent?

What Counts as a Positive Diagnosis?

A system qualifies as biologically viable in APS when:

  • it exhibits constraint closure
  • it responds to perturbation through endogenous reorganisation
  • it maintains viability across time and scale
  • its activity is normatively oriented toward persistence

Failure in any of these dimensions indicates reduced or absent biological organisation.

From Diagnosis to Explanation

APS diagnosis does not replace explanation—it grounds it.

By identifying how a system sustains (or fails to sustain) its own viability, diagnosis provides a basis for:

  • understanding biological function
  • distinguishing living from non-living systems
  • evaluating borderline cases

A Practical Summary

In practice, APS diagnosis follows this sequence:

  • Identify the system as a coherent organisation
  • Assess constraint closure
  • Apply perturbation
  • Evaluate organisational response
  • Assess VG, NG, and CI
  • Evaluate across scale

This sequence transforms biological diagnosis from classification into operational evaluation of living organisation.