Why Agency Must Be Diagnosable

Within APS, agency is the defining activity of life. Living systems are not merely collections of components or mechanisms but viability-oriented organisations that actively maintain the conditions of their own continued persistence. If this claim is to function as a scientific principle rather than a philosophical proposal, agency must be empirically tractable. The central challenge is therefore not simply to define agency, but to determine how agency can be identified, investigated, and evaluated in real systems.

This challenge arises across multiple domains of inquiry. Biologists seek criteria for distinguishing living from non-living systems. Astrobiologists seek methods for detecting life beyond Earth. Synthetic biologists seek to determine whether artificial systems exhibit genuinely life-like organisation. In each case, the underlying question is the same: how can agency be diagnosed?

Recent work in theoretical biology has increasingly argued that agency is fundamental to living systems. Rosslenbroich and colleagues, for example, argue that agency should be understood as an inherent property of living organisms rather than a specialised feature associated only with cognition or complex behaviour. APS shares this broad orientation but extends it in a distinctive direction. If agency is fundamental to life, then biology requires methods capable not merely of recognising agency conceptually but of investigating it empirically. The problem is therefore not only what agency is, but how agency becomes scientifically observable.

APS approaches this problem by treating agency as an observable organisational phenomenon rather than an invisible internal property. Agency becomes tractable because viability-oriented activity leaves detectable traces and generates characteristic responses to changing conditions. The task of diagnosis is therefore to identify and interpret these forms of evidence.

More specifically, APS argues that diagnosis should focus upon viability-oriented agency. The central question is not whether a system merely exhibits activity, complexity, or self-organisation. Many non-living systems display such features. The diagnostic question is whether a system actively contributes to maintaining the conditions required for its own continued persistence. Agency therefore becomes visible through the organisational and regulatory activities through which viability is preserved across time.

Two Paths to Empirical Access

APS identifies two complementary routes through which agency becomes empirically accessible.

The first involves the detection of organisational signatures. These are relatively stable patterns of organisation that indicate the presence of viability-oriented activity. Examples include boundary regulation, self-maintenance, adaptive plasticity, self-repair, and the coordination of processes across multiple scales of organisation. Such signatures provide evidence that a system actively contributes to its own persistence.

The second involves the analysis of perturbation responses. Rather than examining organisational patterns alone, this approach investigates how systems respond when conditions relevant to viability are altered. Perturbations reveal the regulatory dynamics through which living systems preserve themselves, reorganise activity, and recover from disruption.

These approaches are sometimes treated as competing strategies. APS instead treats them as complementary perspectives on the same underlying phenomenon. Organisational signatures reveal the relatively stable structures produced by agency, while perturbation responses reveal the active processes through which agency operates.

Importantly, neither form of evidence possesses independent significance. Both derive their explanatory value from their relationship to viability-oriented agency. Organisational signatures matter because they reflect the historical effects of viability-maintaining activity. Perturbation responses matter because they reveal that activity in operation. Together they provide observational access to the same underlying organisational reality.

The distinction is therefore not between two different kinds of life, but between two different forms of evidence for the same viability-oriented organisation.

Organisational Signatures of Agency

Every persistent living system exhibits organisational features that reflect its viability-oriented activity. These features are not arbitrary traits but recurring patterns generated by the ongoing maintenance of living organisation.

Boundary regulation provides one example. Living systems selectively manage exchanges between themselves and their surroundings, maintaining organisational integrity while remaining coupled to environmental conditions. Homeostatic and homeorhetic processes provide another example. Living systems actively stabilise the conditions required for continued viability despite continual internal and external change.

Constraint closure offers a deeper organisational signature. The activities of living systems contribute to the maintenance of the very constraints that make those activities possible. Organisational persistence therefore becomes visible through the reciprocal relations that sustain viability over time.

Cross-scale coordination provides further evidence. Molecular, cellular, physiological, behavioural, and ecological processes do not operate independently but become integrated within a broader organisational structure oriented toward persistence. Such integration is difficult to explain without recognising the viability-oriented organisation that produces it.

Taken together, these features form organisational signatures of agency. They reveal systems whose structures cannot be adequately understood as passive outcomes of physical processes alone because the organisation itself contributes to maintaining the conditions required for its continuation. The signatures therefore point beyond static organisation toward the agency responsible for sustaining that organisation.

These signatures do not constitute agency themselves. They are evidence of agency. They function as organisational footprints left by the ongoing activity of systems engaged in maintaining their own viability. Diagnostically, they identify candidate agents whose organisation warrants further investigation.

Perturbation as a Diagnostic Tool

Organisational signatures provide important evidence of agency, but they do not reveal how a system responds when viability is challenged. For this reason, APS places particular emphasis on perturbation-based investigation. Perturbations expose the regulatory dynamics through which living systems actively maintain themselves and therefore provide direct access to agency in operation.

A perturbation occurs when conditions relevant to viability are altered. These alterations may be internal or external, minor or severe, temporary or persistent. What matters diagnostically is not the perturbation itself but the system’s response. Living systems characteristically reorganise their activity in ways that preserve viability, restore organisational integrity, or compensate for changing conditions.

This capacity for reorganisation distinguishes viability-oriented systems from many forms of non-living self-organisation. A crystal may maintain a stable structure under suitable conditions, but it does not actively respond to threats to its continued existence. A living system, by contrast, often modifies its behaviour, physiology, development, or ecological interactions in ways that contribute to its own persistence.

Perturbation therefore reveals something that organisational signatures alone cannot fully disclose. It identifies which conditions matter to a system, which processes are mobilised when viability is threatened, and how organisational continuity is actively maintained. In this sense, perturbation does not merely test organisation. It reveals the evaluative structure through which viability-oriented organisation operates.

This diagnostic significance becomes particularly important within APS because evaluation is understood as an intrinsic aspect of viability-oriented agency. Living systems do not merely respond to changing conditions. They respond differentially according to the consequences those conditions have for persistence. Perturbation therefore reveals more than regulatory capacity alone. It provides access to the evaluative organisation through which viability is maintained. Responses become scientifically informative because they disclose what matters to the system and how the system acts to preserve those conditions.

APS consequently treats perturbation as one of the most powerful diagnostic tools available for investigating agency. When a system reorganises activity in response to viability-relevant disturbance, agency becomes directly observable through the system’s own regulatory behaviour.

Viability Gradients and Viability Landscapes

Perturbation becomes particularly informative when viewed in relation to viability itself. APS proposes that living systems occupy regions of possibility within which continued persistence remains achievable. Outside these regions, viability deteriorates and organisational continuity becomes increasingly difficult to maintain.

This perspective allows diagnostic investigation to move beyond simple binary distinctions between life and non-life. Instead of asking only whether a system is viable, APS asks how viability changes under different conditions and how systems respond to those changes. The resulting patterns can be understood as viability gradients.

A viability gradient describes how changes in internal or external conditions alter a system’s capacity to maintain organised persistence. Some changes may have little effect, while others may progressively reduce the system’s ability to sustain itself. Still others may trigger compensatory responses that restore viability despite disruption. The gradient therefore provides information not merely about the state of a system but about the relationship between changing conditions and the system’s capacity for continued persistence.

When these gradients are considered collectively, they form a broader viability landscape. This landscape represents the range of conditions within which a system can continue to persist, the regions in which viability becomes increasingly difficult to maintain, and the thresholds beyond which organisational continuity breaks down.

The concept of a viability landscape provides a particularly powerful way of understanding agency. Agency does not occur independently of viability constraints. Rather, agency operates within viability landscapes by continually regulating activity in relation to changing conditions. Living systems effectively navigate these landscapes through their responses to opportunities, disturbances, and threats. Some forms of activity move a system toward regions of greater viability, while others move it toward regions in which persistence becomes increasingly precarious.

This perspective shifts diagnosis away from static classification and toward dynamic investigation. The central question is no longer simply whether a system satisfies a predefined definition of life. Instead, the question becomes how a system responds as its position within a viability landscape changes. The more systematically a system regulates activity in ways that preserve or restore viability, the stronger the evidence that viability-oriented agency is present.

Viability landscapes also provide a common framework through which organisational signatures and perturbation responses can be interpreted together. Organisational signatures indicate the presence of viability-oriented organisation within particular regions of the landscape, while perturbation responses reveal how that organisation navigates changing conditions. Signatures therefore provide evidence of the organisational consequences of agency, while perturbations reveal agency operating within the landscape itself.

From an APS perspective, this may be one of the most important implications of viability-oriented diagnosis. Agency is not merely detected through isolated traits or behaviours. It becomes visible through the systematic ways in which systems navigate the changing viability conditions associated with continued persistence.

Why Signatures and Perturbations Must Be Integrated

Neither organisational signatures nor perturbation responses are sufficient on their own to diagnose agency comprehensively. Each provides access to a different aspect of viability-oriented organisation, and each becomes more informative when interpreted alongside the other.

Signatures identify candidate agents. They reveal organisational patterns that suggest the presence of viability-oriented activity. Homeostatic regulation, adaptive plasticity, self-repair, and constraint closure all provide evidence that a system actively contributes to its own persistence. Yet signatures alone can sometimes be difficult to interpret. Certain forms of self-organisation may exhibit superficially similar patterns without possessing the regulatory dynamics characteristic of living systems.

Perturbations provide a different form of evidence. They reveal how systems respond when viability becomes threatened. However, perturbation responses are most meaningful when interpreted within an organisational context. A response can only be understood as viability-oriented if the organisational conditions that make viability possible are already known.

APS therefore treats signatures and perturbations as complementary forms of evidence. Signatures identify the organisational structures associated with agency, while perturbations reveal the activity through which those structures are maintained. One provides evidence of organisational continuity; the other reveals the dynamics of organisational maintenance.

Viewed together, these forms of evidence reveal a deeper unity. Organisational signatures provide evidence that viability-oriented agency has been operating over time. Perturbation responses reveal that same agency acting in the present. The former captures the relatively stable products of agency, while the latter captures agency in operation. Diagnosis becomes most powerful when both perspectives converge upon the same underlying organisational interpretation.

Agency becomes diagnostically tractable when both forms of evidence converge. A system exhibiting organisational signatures consistent with viability-oriented activity and demonstrating regulatory responses to viability-relevant perturbations provides substantially stronger evidence of agency than either form of evidence alone.

The central APS insight is therefore not that diagnosis requires signatures or perturbations, but that both are observational windows onto the same underlying phenomenon: viability-oriented agency.

Diagnosing Marginal Cases

The integration of organisational signatures and perturbation responses becomes particularly valuable when investigating marginal or controversial cases. Many systems occupy regions near the boundaries of conventional biological classifications, making diagnosis difficult when based solely on component lists or traditional definitions of life.

Viruses provide a familiar example. Viral systems possess continuity, heredity, and evolutionary capacity, yet their dependence upon host organisms raises questions about whether they constitute autonomous living systems. Organisational signatures may reveal some aspects of viability-oriented organisation, while perturbation-based investigation can help determine the extent to which regulatory activity is genuinely attributable to the virus itself rather than to the host system within which it operates.

From an APS perspective, the central issue is not whether viruses satisfy a predefined checklist of biological properties. The issue is whether evidence converges upon the presence of viability-oriented agency. Organisational signatures and perturbation responses therefore become complementary tools for investigating how much agency is attributable to the viral system itself, how much remains dependent upon host organisation, and how these relationships change across different contexts.

Protocells, synthetic biological constructs, and other experimentally created systems present similar challenges. Such systems may exhibit some signatures associated with living organisation while lacking others. Perturbation analysis allows investigators to examine whether these systems actively preserve viability under changing conditions or merely display transient forms of self-organisation.

APS therefore replaces binary classification with a more nuanced diagnostic framework. Rather than asking whether a system possesses a fixed set of defining properties, APS investigates the degree to which organisational signatures and perturbation responses jointly support the presence of viability-oriented agency. Marginal cases become scientifically informative precisely because they illuminate the conditions under which agency emerges, persists, and breaks down.

Life Detection Beyond Earth

The same diagnostic framework extends naturally to astrobiology and the search for life beyond Earth. One of the central challenges of life detection is that direct observation of agency may be impossible. Investigators often have access only to traces, residues, environmental modifications, or other indirect forms of evidence.

In such contexts, organisational signatures become especially important. Persistent chemical disequilibria, complex boundary structures, self-maintaining environmental patterns, and other forms of organised continuity may provide evidence that viability-oriented activity has occurred. These signatures function as indicators of agency even when the underlying system cannot be directly observed.

Yet APS also recognises the limitations of signatures alone. Many apparent biosignatures may have non-biological explanations. For this reason, APS interprets life detection as a process of evaluating converging lines of evidence rather than identifying a single decisive marker. The stronger the integration among organisational signatures, the stronger the inference that viability-oriented activity may be present.

This perspective represents a subtle but important shift in emphasis. Traditional approaches to life detection often focus upon identifying characteristic biological traits, molecular signatures, or chemical markers. APS instead focuses upon identifying evidence consistent with viability-oriented agency. The question is not merely whether a particular chemical pattern resembles known biology. The question is whether the available evidence supports the existence of a system actively engaged in maintaining conditions necessary for its own persistence.

Where perturbation-based investigation becomes possible, diagnostic confidence can increase substantially. Experimental manipulation, environmental monitoring, or longitudinal observation may reveal regulatory responses consistent with agency. In this way, APS provides a framework capable of integrating indirect and direct forms of evidence within a unified theory of life detection.

The significance of this approach extends beyond astrobiology. It demonstrates that agency can remain diagnostically accessible even when conventional biological assumptions concerning chemistry, morphology, or evolutionary history are unavailable. By focusing on viability-oriented organisation rather than particular biological materials, APS seeks to provide a framework capable of investigating unfamiliar forms of life without presupposing that they resemble terrestrial organisms.

Toward an Empirical Programme of Agency

The broader significance of APS lies in its transformation of agency from a philosophical concept into an empirical research programme. If agency is the defining activity of life, then scientific investigation requires methods capable of identifying, evaluating, and comparing agency across diverse systems and contexts.

Recent theoretical developments have increasingly argued that agency must occupy a central place within biological explanation. APS accepts this conclusion but insists that agency must also become scientifically investigable. The challenge is therefore not merely conceptual but methodological. A theory that places agency at the centre of life must also explain how agency can be recognised, analysed, and compared across different systems.

Organisational signatures provide one route to empirical access. They reveal the stable organisational patterns produced by viability-oriented activity and allow investigators to identify candidate agents. Perturbation responses provide another route. They reveal the regulatory dynamics through which living systems preserve viability and expose the evaluative structure that guides their activity.

Together these approaches establish a unified framework for diagnosis. Signatures reveal the organisational footprints of agency, while perturbations reveal agency in operation. Neither replaces the other. Instead, both contribute complementary evidence concerning the same underlying phenomenon.

This integration offers a common framework for biological diagnosis, life detection, synthetic biology, origins-of-life research, and the investigation of marginal cases. More fundamentally, it demonstrates that viability-oriented agency is not merely a theoretical abstraction but an empirically tractable feature of living systems.

APS therefore reframes diagnosis itself. The central question is no longer whether a system possesses a predefined list of biological traits. The question becomes whether organisational evidence and regulatory evidence converge upon the existence of a system actively engaged in maintaining the conditions of its own persistence.

Diagnosis consequently becomes the empirical investigation of viability-oriented agency. Organisational signatures reveal the relatively stable consequences of that agency, while perturbation responses reveal the regulatory activities through which it operates. Together they provide complementary windows onto the same underlying phenomenon: the active maintenance of organised persistence.

Continue Exploring

  • How to Diagnose a Biological System
  • Diagnosis as Continuity Analysis
  • Life Detection in APS
  • Malfunction, Breakdown, and Death
  • Agency as the Defining Activity of Life

Key Point

Agency becomes empirically tractable when organisational signatures and perturbation responses are investigated together. Organisational signatures reveal the relatively stable footprints of viability-oriented activity, while perturbation responses reveal the regulatory dynamics through which viability is maintained. Their integration provides a unified framework for diagnosing living systems across biological, synthetic, and astrobiological contexts. Within APS, diagnosis ultimately becomes the empirical investigation of viability-oriented agency.