TY - JOUR AB - Purpose Complex systems adapt to survive, but little comparative literature exists on various approaches. Adaptive complex systems are generic, this referring to propositions concerning their bounded instability, adaptability and viability. Two classes of adaptive complex system theories exist: hard and soft. Hard complexity theories include Complex Adaptive Systems (CAS) and Viability Theory, and softer theories, which we refer to as Viable Systems Theories (VSTs), that include Management Cybernetics at one extreme and Humanism at the other. This paper has a dual purpose distributed across two parts. In Part 1, the purpose of this paper is to identify the conditions for the complementarity of the two classes of theory. In Part 2, the purpose is to explore (in part using Agency Theory) the two classes of theory and their proposed complexity continuum.Design/methodology/approach A detailed analysis of the literature permits a distinction between hard and softer approaches towards modelling complex social systems. Hard theories are human-incommensurable, while soft ones are human-commensurable, therefore more closely related to the human condition. The characteristics that differentiate between hard and soft approaches are identified.Findings Hard theories are more restrictive than the softer theories. The latter can embrace degrees of “softness” and it is explained how hard and soft approaches can be mixed, sometimes creating Harmony.Originality/value There are very few explorations of the relationship between hard and soft approaches to complexity theory, and even fewer that draw in the notion of harmony. VL - 48 IS - 6 SN - 0368-492X DO - 10.1108/K-06-2018-0337 UR - https://doi.org/10.1108/K-06-2018-0337 AU - Yolles Maurice PY - 2018 Y1 - 2018/01/01 TI - The complexity continuum, Part 1: hard and soft theories T2 - Kybernetes PB - Emerald Publishing Limited SP - 1330 EP - 1354 Y2 - 2024/04/23 ER -