Interaction system
An interaction system is a form of social system in Niklas Luhmann's theory of communicative autopoiesis. It is the most elementary and ephemeral type of social system, produced by the physical or virtual co-presence of multiple participants who can perceive each other and adjust their behavior accordingly. Unlike organizations or mass media systems, interaction systems do not persist beyond the moment of interaction; they dissolve when the participants disperse.
The defining feature of an interaction system is its closure mechanism: presence. The system exists only as long as the participants are mutually present and perceivable. A conversation is the paradigm case: it generates its own topics, turn-taking rules, and relational definitions, and it maintains itself by continuously producing new utterances that refer to prior ones. The moment the participants leave the room or end the call, the interaction system ceases to exist. Its elements — the utterances — have no existence outside the ongoing present.
In Luhmann's framework, interaction systems are distinct from the psychic systems (consciousnesses) of the individual participants and from the broader social systems (organizations, functional systems) that may observe or record the interaction. A conversation is not the same as the consciousnesses of the people having it, nor is it the same as the organization that might later use the conversation as a decision premise. It is a sui generis system with its own autopoiesis.
The concept of interaction system is important because it shows that social systems do not require permanence or material infrastructure to be operationally closed. A conversation is closed because only utterances in the conversation can produce further utterances in the conversation. The closure is temporal, not spatial. This answers the material boundary problem that critics raise against communicative autopoiesis: the boundary is not a membrane but a moment — the continuous present of the interaction.
Interaction systems are structurally coupled with both psychic systems and organizational systems. The participants' consciousnesses perturb the interaction system by producing utterances, and the interaction system perturbs the participants' consciousnesses by producing utterances that must be processed. Organizations perturb interaction systems by providing decision premises that constrain what can be said (e.g., a meeting agenda), and interaction systems perturb organizations by producing decisions that enter the organizational memory.