What is a Complex System?

J.A.C Ladyman, J. Lambert, Karoline Wiesner

Research output: Contribution to journalArticle (Academic Journal)peer-review

430 Citations (Scopus)


Complex systems research is becoming ever more important in both the natural and social sciences. It is commonly implied that there is such a thing as a complex system, different examples of which are studied across many disciplines. However, there is no concise definition of a complex system, let alone a definition on which all scientists agree. We review various attempts to characterize a complex system, and consider a core set of features that are widely associated with complex systems in the literature and by those in the field. We argue that some of these features are neither necessary nor sufficient for complexity, and that some of them are too vague or confused to be of any analytical use. In order to bring mathematical rigour to the issue we then review some standard measures of complexity from the scientific literature, and offer a taxonomy for them, before arguing that the one that best captures the qualitative notion of the order produced by complex systems is that of the Statistical Complexity. Finally, we offer our own list of necessary conditions as a characterization of complexity. These conditions are qualitative and may not be jointly sufficient for complexity. We close with some suggestions for future work.
Translated title of the contributionWhat is a Complex System?
Original languageEnglish
Pages (from-to)33-67
Number of pages35
JournalEuropean Journal for Philosophy of Science
Issue number1
Early online date19 Jun 2012
Publication statusPublished - Jan 2013

Structured keywords

  • Centre for Science and Philosophy
  • Centre_for_science_and_philosophy


  • complexity
  • statistical complexity
  • information
  • complex system

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