APS and Systems Theory — Similarities, Differences, and Limits

Abstract

Systems theory provides powerful tools for describing interaction, feedback, and dynamics in biological systems. This article clarifies the relationship between systems approaches and the APS framework. While APS incorporates key insights from systems theory, it diverges by grounding biological organisation in viability-oriented, constraint-closed activity. APS shows that not all systems are biological and that biological systems are defined not by complexity or feedback alone, but by endogenous normativity and agency.

Systems Theory and the Study of Organisation

Systems theory encompasses a broad set of approaches that model phenomena in terms of interacting components, feedback loops, and dynamic behaviour. In biology, these approaches have been central to moving beyond strictly reductionist explanations.

Rather than analysing isolated parts, systems approaches examine how interactions among components produce organised behaviour over time. Concepts such as feedback, regulation, stability, and emergence are central to this perspective. APS treats such phenomena organisationally rather than as unexplained higher-order properties. See Emergence in Biology — An APS Clarification.

These tools have proven extremely powerful for describing biological systems, from metabolic networks to ecological dynamics. In this respect, systems theory captures an important aspect of living organisation: that biological phenomena are distributed across interacting processes rather than located in isolated components.

Points of Convergence with APS

APS shares several core commitments with systems approaches.

Both reject the idea that biological explanation can be reduced to isolated parts. Both emphasise that organisation arises through interaction, and that behaviour must be understood in terms of processes unfolding across time and scale.

Systems concepts such as feedback, coupling, and dynamic stability align naturally with APS descriptions of how living systems sustain themselves. In particular, the emphasis on distributed causation resonates with APS’s view that agency, process, and scale are co-constitutive.

For these reasons, systems theory provides an important descriptive and analytical toolkit within an APS framework. APS therefore preserves the explanatory strengths of systems approaches while rejecting the idea that formal system description alone exhausts biological explanation. See Reductionism in Biology — An APS Clarification.

APS Box — How APS Relates to Other Theoretical Frameworks

Contemporary frameworks such as control theory and nonlinear dynamical systems theory provide powerful and indispensable accounts of living systems. They explain how systems regulate their behaviour, maintain stability, and exhibit complex dynamics across time.

APS does not replace these approaches, nor does it reduce them to a single underlying model. Instead, it addresses a different question: what kind of organisation makes a system a living system in the first place.

Multiple theoretical frameworks can therefore apply to the same system, but they do so in different ways and address different explanatory questions. A dynamical systems description may characterise the system’s trajectories, and a control-theoretic model may describe its regulatory structure. These accounts are often non-reducible to one another, and each can be independently valid.

However, such accounts do not by themselves distinguish living systems from non-living systems. Many non-living systems also exhibit regulation, feedback, and complex dynamics.

APS contributes by specifying the organisational conditions under which a system must actively maintain its own viability. A system is viability-oriented when its processes are organised such that their effects contribute, directly or indirectly, to maintaining the conditions required for the system’s continued existence.

Importantly, in APS, viability is not defined by reference to life itself. It is specified in terms of the persistence of an organised system within a bounded region of possible states. A living system is therefore not defined in a circular sense as “that which maintains viability”, but as a system whose organisation is structured around maintaining these conditions.

In this sense, APS provides a way of identifying what makes a system a living system, rather than a general account of everything such a system does.

This does not mean that APS provides a complete or self-sufficient account of living systems. Describing how such systems behave, regulate, and evolve requires additional theoretical frameworks. APS specifies conditions that are necessary for identifying living systems, but it does not by itself exhaust the explanations required to understand them.

A complete scientific understanding of living systems therefore requires multiple forms of explanation. Dynamical and control-theoretic accounts explain how systems behave and regulate. APS clarifies the conditions under which such systems count as living systems at all.

Key Point:
Explaining regulation, dynamics, or behaviour is not the same as explaining what makes a system a living system. APS addresses this latter question by specifying the organisational conditions under which viability is maintained.

The Limits of Systems Theory

Despite these strengths, systems theory typically remains normatively neutral. It can describe how systems behave, but it does not, by itself, establish what makes a system biological.

In many systems approaches, the definition of the system itself—its boundaries, variables, and relevant processes—is introduced by the observer. This is sufficient for modelling and analysis, but it does not establish what makes a system biological.

As a result, systems theory can be applied equally to:

living organisms
mechanical devices
economic systems
climate dynamics

The same formal tools describe all of these cases, but they do not distinguish between them in terms of their mode of organisation. This also helps explain why similar functional patterns may be realised across very different material systems without thereby erasing the distinction between biological and non-biological organisation. See Multiple Realization and Biological Organisation.

APS: From Systems to Biological Organisation

APS incorporates the insights of systems theory while specifying the conditions under which a system counts as biological.

In APS, biological systems are not defined by complexity, feedback, or dynamic behaviour alone. They are defined by viability-oriented, constraint-closed organisation.

In this sense, purpose in living systems is not externally imposed design, but the organisation of activity relative to viability.

This introduces a fundamental distinction:

In general systems theory, interactions can be described without reference to what is at stake for the system
In APS, interactions are organised around the maintenance of the system’s own persistence

This gives rise to endogenous normativity. Processes matter because they contribute to or undermine the continued viability of the system. This is not imposed by the observer but arises from the organisation of the system itself. This differentiation is a form of evaluation: the ongoing modulation of activity in relation to what supports or undermines persistence. This viability-based normativity grounds biological function as the normatively structured contribution of processes to persistence.

System Boundaries and Organisational Closure

A central difference concerns how system boundaries are understood.

In many systems approaches, boundaries are defined for analytical convenience. The system is whatever is selected for study, and its limits depend on the modelling framework.

In APS, boundaries are not arbitrary. They are determined by constraint-closed organisation—the network of processes that mutually sustain one another and collectively maintain the system’s persistence.

This means that a biological system is not simply a set of interacting components but a self-delimiting organisation. Its boundaries are enacted through its own activity, not imposed from outside.

Agency and the Distinction Between Living and Non-Living Systems

Because systems theory is normatively neutral, it does not by itself distinguish between living and non-living systems.

APS introduces this distinction through the concept of biological agency. Living systems actively regulate the conditions of their own persistence. They do not merely exhibit dynamic behaviour; they sustain themselves through ongoing, viability-oriented activity.

This distinguishes biological systems from:

machines, which typically operate according to externally imposed functions
physical systems, which evolve according to general laws without self-maintained organisation

In APS terms, agency is not an additional feature layered onto a system. It is the activity through which a system maintains itself as a system.

Systems, Organisation, and the Appearance of Cognition

Because systems theory can describe complex, adaptive, and dynamically stable behaviour, it is often used to model systems that appear intelligent or cognitively organised, including artificial, computational, and social systems.

From an APS perspective, this descriptive power does not imply that such systems instantiate cognition.

Cognition, in APS, is not defined by behavioural complexity, feedback, or dynamical organisation alone. APS therefore distinguishes biological organisation from adaptive systems in general. Artificial, computational, or cybernetic systems may exhibit feedback, regulation, optimisation, and distributed coordination without participating in viability-oriented self-maintaining persistence. Behavioural sophistication alone is therefore insufficient for biological agency or cognition.

From an APS perspective, this descriptive power does not imply that such systems instantiate cognition.

Cognition, in APS, is not defined by behavioural complexity, feedback, or dynamical organisation alone. It is a mode of viability-oriented, constraint-sensitive organisation found in systems that regulate their own conditions of persistence.

APS therefore distinguishes biological organisation from adaptive systems in general. Artificial, computational, or cybernetic systems may exhibit feedback, regulation, optimisation, and distributed coordination without participating in viability-oriented self-maintaining persistence.

Behavioural sophistication alone is therefore insufficient for biological agency or cognition. For further discussion, see Why AI Is Not Biological Agency and Why Life Is Not Intelligence.

Many non-biological systems can exhibit sophisticated forms of coordination, adaptation, or optimisation. However, they do not sustain themselves as systems, do not generate their own conditions of existence, and do not operate through constraint-closed organisation.

For this reason, systems theory can describe the behaviour of both living and non-living systems using similar formal tools, but only living systems exhibit cognition in the APS sense.

Systems Theory Within APS

From an APS perspective, systems theory is best understood as a descriptive and analytical layer rather than a complete account of life.

It provides tools for modelling:

interactions
feedback structures
dynamical trajectories

APS situates these tools within a broader explanatory framework that specifies:

why certain processes matter (viability)
how organisation is maintained (constraint closure)
what distinguishes living systems (agency)

In this way, systems theory is neither rejected nor replaced. It is integrated and grounded within an account of biological organisation.

Key Point

Systems theory describes patterns of interaction and dynamic organisation, but life is defined by viability-oriented organisation.