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Systems thinking: a select glossary

Updated Monday, 11 October 2021
Get to grips with the terms which drive systems thinking.

Woman thinking

This glossary contains definitions of some generalized system concepts used in Systems Practice. What is a mess? and how does it differ from a difficulty? Find out here!

One of the key principles in Systems Thinking is feedback.

If you want to know more about Systems Thinking, the Open University course T205 Systems Thinking, Principles and Practice is an excellent introduction to the discipline.

Definitions of some generalized system concepts used in systems practice.


The borders of the system, determined by the observer(s), which define where control action can be taken: a particular area of responsibility to achieve system purposes.

Closed system

A system which is closed to inputs from its environment, e.g. a transistor radio is closed to energy. In practice such systems rarely exist, but many systems are treated as if they were closed.


(i) First-order communication is based on simple feedback (as in a thermostat) but should not be confused with human communication, which has a biological basis.

(ii) Second-order communication is understood from a theory of cognition which encompasses language, emotion, perception and behaviour. Amongst human beings this gives rise to new properties in the communicating partners who each have different experiential histories.


Logical dependence between components or elements (including sub-systems) within a system.


A situation considered as a bounded and well defined problem where it is assumed that it is usually clear who is involved and what would constitute a solution within a given time frame.

Emergent properties

Properties which are revealed at a particular level of organization and which are not possessed by constituent sub-systems. Thus these properties emerge from an assembly of sub-systems.


That which is outside the system boundary and which affects the behaviour of the system; alternatively the 'context' for a system of interest.


A form of interconnection, present in a wide range of systems. Feedback may be negative (compensatory or balancing) or positive (exaggerating or reinforcing)
Want to know more? Explore positive and negative feedback.


Layered structure; the location of a particular system within a continuum of levels of organization. This means that any system is at the same time a sub-system of some wider system and is itself a wider system to its sub-systems.


A constructed system, of interest to one or more people, used in a process of inquiry; a term suggested to avoid confusion with the everyday use of the word 'system', as in e.g. 'transport system' (used synonymously with 'system of interest').

Measure of performance

The criteria against which the system is judged to have achieved its purpose. Data collected according to measures of performance are used to modify the interactions within the system.


A mess is a set of conditions that produces dissatisfaction. It can be conceptualized as a system of problems or opportunities; a problem or an opportunity is an ultimate element abstracted from a mess.

Monitoring and control

Data collected and decisions taken in relation to measures of performance are monitored and controlled and action is taken through some avenue of management.


An elaboration of the concept of hierarchy which avoids the human projection of 'above' and 'below' and recognizes an assemblage of entities in relationship, e.g. organisms in an ecosystem.

Open system

A system which is open to its environment such that there are recognizable inputs to the system and outputs to the environment, e.g. an organism is an open system for inputs of food (energy).


A way of experiencing which is shaped by our personal and social histories, where experiencing is a cognitive act.


Objective, goal or mission of the system; the raison d'être which in terms of a model developed by people is to achieve the particular transformation that has been defined.


Elements which are available within the system boundary and which enable the transformation to occur.


An integrated whole whose essential properties arise from the relationships between its parts from the Greek synhistanai, meaning 'to place together'.

System of interest

The product of distinguishing a system in a situation in which an individual or group has an interest or stake.

Systems thinking

The understanding of a phenomenon within the context of a larger whole; to understand things systemically literally means to put them into a context, to establish the nature of their relationships.


Literally, a network of pre-understandings or prejudices from which we think and act; how we make sense of our world.


Changes, modelled as an interconnected set of activities which convert an input to an output which may leave the system (a 'product') or become an input to another transformation.


A way of thinking which is inappropriate for the context or issue being explored.


That view of the world which enables each observer to attribute meaning to what is observed (sometimes the German word Weltanschauung is used synonymously).


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