International Encyclopedia of Systems and Cybernetics

"a) A section of a hierarchy which is defined by a scale",

"b) The scale of an observation" (T.F.H. ALLEN & T.B. STARR, 1982, p.271).

M. BUNGE emphasizes that… "a level is not a thing but a set and therefore a concept, though not an idle one, Hence levels cannot act upon on another". All talk of interlevel action is elliptical or metaphorical, not literal" (1979, p, 13). Formerly, BUNGE also wrote: "A level is a section of reality characterized by a set of interlocked properties and laws, some of which are peculiar to the given domain, and which are assumed to have emerged in time from other (lower or higher) levels existing previously" ("Metascientific queries", 1959, p.8).

M. MESAROVIC, D. MACKO and Y. TAKAHARA introduce three different notions of level: "1) the level of description or abstraction; 2) the level of decision complexity, and 3) the organizational level. To distinguish between these notions, we use the terms "strata", "layers" and "echelons" respectively. The term "level" is reserved as a generic term referring to any of these notions when there is no need to emphasize the distinction. We point out that, in the description of an actual hierarchical system, all three notions might be involved; the case where only one notion is applicable is an exception rather than the rule" (1970, p.37).

ALLEN and STARR state: "Many different entities may be observed scaled to a certain level distributed horizontally across a hierarchy" (p.271).

Complex systems are necessarily multi-leveled, as the harmony of their different subsystems requires the shaping of hierarchic controls or distributed and interconnected regulations, and each subsystem is in turn made of elements or parts and acts as their coordinator.

F.E. EMERY states that "in analysis of any one level of a system's organization it probably would be adequate to consider only the ones inmediately above and below" (1969, p.15).