Structures are conditions that limit the Domain of connectivity of system operations: they are the conditions for the →Autopoiesis of every system.
The concept of structure describes the selection of the relations between elements that are accepted in the system.
In →meaning-constituting systems, structures cannot merely consist of the relations between elements, since elements are events without duration [→Event]: with their disappearance, the relations also would disappear, and with them the system itself.
The selections that become structurally relevant are those that limit the possibilities of recombining the elements (communications or thoughts).
This means, first, that structure and system are not coterminous. Although there can be no structureless systems, and structures can only ever be structures in a system, the two terms describe two completely different findings: whereas elements of a system are operations that, as such, must be constantly reproduced, structures condense only by repeating the identical in different combinations. Thus, the identity of the system can be maintained when its structures change. The same goes for objects, situations, periods of time, people, and so on: in all these cases, it is about meaningful combinations that become more significant as structures when it is possible to generalize their identity beyond each moment in which they take place.
Structures can also be described as selections of selections because they limit the connectivity (first selection), based on which the system produces its own elements (second selection). Without structures, the system could not determine whether its own further operations even occur: on the contrary, it would find itself confronted with the indeterminacy of the connections and therefore the impossibility of continuing its autopoiesis. The complexity of the system is made determinable by building structure, and the selectivity of the individual events is maintained and re-introduced in the next event as a range of possibilities from which the next selection can be obtained.
In this sense, structures guarantee the existence of the system not because of their stability, but for the sole reason that they can secure the transition from one operation to the next. The stability of the system must therefore be thought of as “dynamic stability,” because the continuity of the system is only guaranteed by the discontinuity of its operations. Structures are maintained when they are repeated and condensed in various situations, otherwise they will be forgotten.
In the case of social systems, structures are the structures of →expectations that reveal possibilities of communication that the system can orient itself towards: by constructing expectations, a social system can determine connections and therefore also operative possibilities. Without structure, communication could decide neither which topics can be discussed, nor clarify who should begin to communicate when. Autopoiesis and structure of social systems, therefore, do not coincide: operations – i.e., system elements – are communications, whilst the structural elements are expectations.
From a temporal Point of View, structures guarantee the reversibility of selections, although, as events, selections disappear irreversibly into the past. The structure admits duration against the background of the temporal punctuality of events and, therefore, also admits the re-actualization of situations in which new operations must be selected. Thanks to its structures, a system can recall past situations or imagine future ones by abstracting from the unceasing perpetuation of operations. In this sense, structures make the selectivity of communication visible, as well as revealing the possibility of different directions for selections.
Structures can change; the system is therefore capable of learning. We can only speak of learning in relation to structures, because events cannot be changed: they occur and then instantly disappear. Only their information value is surprising and introduces novelties compared to what the system expects on the basis of its structures. [G.C.]
Social Systems (1995: Ch. 8); Introduction to Systems Theory (2012: 239-247).