An agent is a representation of an action. One action may not have
more than one agent, but a single agent may cause more than one action.
The necessity of this representation is seen when we describe
a human being and want to distingush between the human's body and
and the way (s)he acts. Generally, the concept of agent takes on the
cybernetic description of some part of reality, and leaves
physical (as well as chemical and bioligical) description to physics
When we speak of an action, we speak also of an agent that performs
the action. An agent is the carrier of will, the entity that chooses
between possible actions. We do not see agents, we see only what they
are doing. But we use the concept of agent to create models of the world.
We break what is going on in the world into parts and call these parts
actions. Then we notice that actions have certain structure. Some actions
are taking place in parallel, others consecutively. A number of actions
can be considered as one complex action (cf. process). We start the description
of this structure by introducing the notion of agents that perform actions.
The same agent may perform, consecutively, some number of actions.
Different agents may execute actions in parallel. The agent of a complex
action can, somehow, call a "subcontractor" agent.
Introduction of agents is, speaking informally, our first theory
of the world. Further development of the theory can go in various
directions. Since the thinking being understands agent seeing himself
as the primary model, it is natural that in primitive societies the concept
of agent is understood anthropomorphically: as something which is very
similar, if not identical, to ourselves. Hence the animism of primitive
thinking: understanding of all actions as initiated by various kinds
of spirits or other imaginary creatures.
The development of modern science banned spirits from the picture of the
world. But agents, cleared from anthropomorphism, still remain,
even though the physicists do not call them so. What is Newtonian force
if not an agent that changes, every moment, the momentum of a body?
Physics concentrates on the description of the world in space and
time; it leaves -- at least at the present day -- the concept of angent
implicit. We need it explicitly because of our metaphysics based
on the concept of action, not to mention the simple fact that cybernetics
describes, among other things, the behavior of human agents.
(This last field of application of cybernetics is, of course, one of the
reasons for our metaphysics).