"A compound thing , the components of which are not coupled, linked, connected, or bounded" (M. BUNGE, 1979, p.4).
BUNGE gives as examples a celestial constellation, or a random sample of a biological population.
The only significative character of aggregates is a certain localization in space and permanence in time.
C. ZELLER constructed some models in order to establish the conditions of stability of aggregates (1967, p.53-55). This author states, for instance, that, in the case of geometric elements in a plane, stability " … is reached when six neighbours are gathered around a base element". (See: "Hexagonal space filling")
It depends, besides, on the shape of the elements, on the initial conditions and, probably on the nature of the substrate.
The relations among elements are thus not absolutely random. The aggregate, when submitted to certain variations of its environment may offer a degree of collective behavior which may even become repetitious and correspond to characterized processes, as for example directional growth.
The theory of criticality studies the behavior of such typical aggregates as snow or sand banks or the characteristics of aggregative phenomena as bush and forest fires, mud slides or stock market panics.
According to A. ANGYAL "Wholes cannot be compared to additive aggregations at all…
"In aggregates is is significant that the parts are added; in a system it is significant that the parts are arranged" (1969, p.26).
And, besides:" … aggregation and whole formation are processes of an entirely different order" (p.27)
It remains nevertheless true that aggregates seem in some cases to be the forerunner of association and differentiation.
According to V. KREMYANSKIY: "In chaotic aggregates, the interconnections between the elements are comparatively uniform, but they are particularly simple when a relative organizational simplicity typifies the elements themselves. The nature of the elements is not changed by entering or leaving the aggregate. Where there is a large number of elements, changes in the chaotic whole depend more on changes in many elements than on solitary or small groups of elements. The total of its internal interconnections, and hence the internal conditioning of the changes, bears a predominantly statistical or "probability" character". (1969, p.126-7)
Some authors use the term "congeries" (plural) as a substitute for aggregate.