World Futures, 64: 305–320, 2008 Copyright c  Taylor & Francis Group, LLC ISSN 0260-4027 print / 1556-1844 online DOI: 10.1080/02604020802301105 INTRODUCTION TO THE MODEL OF HIERARCHICAL COMPLEXITY AND ITS RELATIONSHIP TO POSTFORMAL ACTION MICHAEL LAMPORT COMMONS Department of Psychiatry, Harvard Medical School, Cambridge, Massachusetts, USA The Model of Hierarchical Complexity is introduced in terms of its main concepts, background, and applications. As a general, quantitative behavioral developmen- tal theory, the Model enables examination of universal patterns of evolution and development. Behavioral tasks are definable and their organization of information in increasingly greater hierarchical, or vertical, complexity is measurable. Fifteen orders of hierarchical complexity account for task performances across domains, ranging from those of machines to creative geniuses. The four most complex orders are demonstrated by postformal stages of thought, which measure beyond formal operations, the highest stage found by Piaget for adults. KEYWORDS: Behavioral, development, evolution, information, Model of Hierarchical Complexity, performance, postformal, stages, tasks. This introduction to the Model of Hierarchical Complexity describes its basic terms and concepts, presents the orders of complexity and transition steps between stages of performance, introduces applications of the Model, and lays out its historical origins. The last 4 of the 15 stages of hierarchical complexity are referred to as postformal thought, highlighted in this special issue. Thought is action. These stages are briefly introduced here, and other articles in this issue will bring those and many other stages to life. The Model of Hierarchical Complexity (MHC) (Commons, Trudeau, Stein, Richards, and Krause, 1998; Commons and Richards, 1984a, 1984b) offers a stan- dard method of examining the universal patterns of evolution and development. It is a quantitative behavioral developmental theory (the formal theory is presented separately in this issue). There are two kinds of hierarchical complexity. The com- monly recognized one refers to the ubiquitous linear hierarchies that are described in many fields of study. These are descriptive. By contrast, the Model of Hierar- chical Complexity offers a standard method of examining the nonlinear activity of constructing the universal patterns of evolution and development. It accounts for evolution and development by recognizing their patterns are comprised of tasks, Address correspondence to Michael Lamport Commons, Ph.D., Dare Institute, 234 Huron Ave., Cambridge, MA 02138-1328, USA. E-mail: commons@tiac.net 305