The Ontology of Complexity: The Hierarchical Emergence of Nested Constraints

Complexity is ubiquitous yet elusive. From molecules to cells, from organisms to ecosystems and societies, systems exhibit widely different degrees of hierarchical organization, but a unified ontological account of complexity remains lacking. This paper develops an interpretation of complexity within Energy-Efficiency Theory (EET). Starting from minimal EET premises, it proposes that complexity is the hierarchical emergence of nested constraints: complexity arises when constrained-state energy at one scale becomes the reusable substrate for a higher-order constrained structure, with each level maintained through its own Energy-Efficiency Cycle (EEC). The framework distinguishes structural complexity from dynamical complexity, clarifies the energetic conditions under which a new level can emerge, and argues that complexity is bounded by energy availability, coordination costs, and cross-level coupling constraints. It also introduces operational indices for comparing matched systems and proposes heuristic benchmark relations for future empirical work. These quantitative relations are intended as research tools rather than as universal constants derived solely from EET. The paper therefore does not claim to replace existing complexity measures in a single step; instead, it offers a common ontological language for understanding why nested organization appears across physics, biology, and social systems, and why local complexity increase can remain compatible with global entropy increase.