A holon is something that is simultaneously a whole and a part. The term was coined by Arthur Koestler to describe stable intermediate forms that exist in evolutionary processes. A holon is a self-organizing system composed of other holons that exists at the balance between chaos and order. Holons can be individual entities with their own identity or agency, or social groups with collective identity but no single leader. Artifacts created by holons are also considered holons, though they lack attributes like agency. Holons are useful for understanding complex multi-agent systems.

1. A holon (Greek: ὅλον, holon neuterform of ὅλος, holos"whole") is
something that is simultaneously a whole and a part. The word
was coined by Arthur Koestler in his book The Ghostin the
Machine (1967,p. 48). Koestlerwas compelledby two observations
in proposing the notion of the holon. The first observation was
influenced by Nobel Prize winner Herbert A. Simon's parable of the
two watchmakers—in which Simon concludes that complexsystems
evolve from simple systems much more rapidly when there are stable
intermediate forms presentin that evolutionary process than if they
are not present.[1]
The second observationwas made by Koestler
himself in his analysis of hierarchies and stable intermediate forms in
both living organisms and social organizations. He concluded that,
although it is easy to identify sub-wholes or parts, wholes and parts in
an absolute sense do not exist anywhere. Koestlerproposed the
word holon to describe the hybrid nature of sub-wholes and parts
within in vivo system
A fractal is close to the idea ofholon,as it is a part that represents a
whole at the same time. Do seeds contain trees or do trees contain
seeds?We could say both are true, because 'trees and seeds' is an
example of a holon.

2. General definition
A holon is a system (or phenomenon) that is an evolving self-
organizing dissipative structure, composedof other holons, whose
structures exist at a balance point between chaos and order. It is
sometimesdiscussed in the context of self-organizing holarchic
open systems (or, SOHO systems).[2]
A holon is maintained by the
throughput of matter–energy andinformation–entropyconnected to
other holons and is simultaneously a whole in and itself at the same
time being nested within another holon and so is a part of something
much larger than itself.
Types of holons
Individualholon
An individual holon possessesa dominant monad; that is, it
possessesa definable "I-ness".An individual holon is discrete,self-
contained, and also demonstrates the quality of agency, or self-
directed behavior.[4]
The individual holon, although a discrete and
self-contained whole, is made up of parts; in the case of a human,
examples of these parts would include the heart, lungs, liver, brain,
spleen,etc. When a human exercises agency,taking a step to the
left, for example, the entire holon, including the constituent parts,
moves together as one unit.
Socialholon
A social holon does not possess a dominant monad; it possesses
only a definable "we-ness",as it is a collective made up of individual
holons.[5]
In addition, rather than possessing discrete agency, a social
holon possesseswhat is defined as nexus agency. An illustration of
nexus agency is best described by a flock of geese.Each goose is an
individual holon, the flock makes up a social holon. Although the flock
moves as one unit when flying, and it is "directed" by the choices of
the lead goose,the flock itself is not mandated to follow that lead
goose.Another way to considerthis would be collective activity that

3. has the potential for independentinternal activity at any given
moment.
Artifacts
American philosopher Ken Wilberincludes Artifacts in his theory of
holons. Artifacts are anything (e.g. a statue or a piece of music) that
is created by either an individual holon or a social holon. While
lacking any of the defining structural characteristics - agency; self-
maintenance; I-ness; Self Transcendence - of the previous two
holons, Artifacts are useful to include in a comprehensive scheme
due to their potential to replicate aspects of and profoundlyaffect(via,
say interpretation) the previously describedholons. Artifacts are
made up of individual or social holons (e.g. a statue is made up of
atoms).
The developmentof Artificial Intelligence may force one to question
where the line should be drawn between the individual holon and the
artifact.
Heaps
Heaps are defined as random collections of holons that lack any sort
of organisational significance.A pile of leaves would be an example
of a heap. Note, one could question whether a pile of leaves could be
an "artifact" of an ecosystem "socialholon". This raises a problem of
intentionality: in short, if social holons create artifacts but lack
intentionality (the domain of individual holons) how can we distinguish
between heaps and artifacts? Further, if an artist (individual holon)
paints a picture (artifact) in a deliberately chaotic and unstructured
way does it becomea heap?
Holons in multiagent systems
Multiagent systems are systems composedof autonomous software
entities. They are able to simulate a system or to solve problems.A
holon, just like an agent, is an intelligent entity able to interact with
the environment and to take decisions to solve a specificproblem.
Holon has the noteworthy property of playing the role of a whole and
a part at the same time. This reflects at the organizational level:
holarchy functions first as autonomous wholes in supra-ordination to
their parts, secondly as dependentparts in sub-ordination to controls
on higher levels, and thirdly in coordination with their local
environment.[6]

4. The SARL agent-oriented programming language is a language that
has a native supports of the conceptof holon. The associated run-
time environment Janus enables to run the implemented holons.