Autonomous agents are situated in some environment. Change the environment and we may no longer have an agent. A robot with only visual sensors in an environment without light is not an agent. Systems are agents or not with respect to some environment. It neither plans nor learns.
Agents can exist alone or as a society.
A society may be divided into subsocities, grops, subgroups, teams, etc. Concepts, Kinds, and Cognitive Development. Langton, Christopher, ed.