Cybernetics & Human Knowing' Vol.9, No.34,2002, pp. 55-78 Spencer-Brown, Luhmann and Autology Michael Schiltz & Gen Verschraegenl Abstract: In this article we try to show how a social theory can be constructed which takes the requirement of self-implicatio n ot autology serious. For this purpose, we turn to Niklas Luhmann's theory of self-referential. autopoietic systems. For it is our thesis that the specific conatus of Luhmann,s enterprise is to construct an autological social theory, i.e. a theory which is sufficiently complex to imply itself, to describe itself in the course of describing its objects of investigation. To demànstrate this claim, the line of argument has firmly been rooted in George Spencer-Brown's l-zzw of Fornrs,a work central to systems theory. The architecture of Luhmann's Systems theory is thus presented in accordance with Spencer-Brown's calculus of indications. Special attention is being paid to systems theory's Leitdffirenz system/environment. For this distinction is literally maintained as the alpha and the omega of the theory: the Leítdiffererza carries theoretical observations, and at the same time permits the self-observation. By means of the figure of 're-entry', drawn from Spencer-Brown's calculus, we show horv the starting distinction between system and environment, can 're-enter' the construction founded upon it and makes it possible for the theory to observe itself as a system within an environment' 1. Introduction: systems Theory and the Requirement of Autology Niklas Luhmann describes his theory of autopoietic self-referential social systems as a universalistic theory (Luhmann, t99511984, p. 10). The implications of such a claim are vast and can hardly be underestimated' Not only does Luhmann maintain that it is able to describe and reconstruct everything social (Luhmann, 1g97,p.16); he also argues that, as a corollary of this claim, his theory of social systems is applicable to itself, i.e. that the theory appears to itself as a possible object of investigation. Such self-reflection is in no way to be taken as an un"necessary intellectual tour-de-force, ÍroÍ ought it be misconstrued as some form of theoretical self-inflation. In fact, the opposite is the case. We contend that, to be fully acceptable, a sociological theory must also be about itself' For no sociological statement, no essay and no theory can say anything about society withouialso being part of society itself. Social theories arise, as all theories do, within a social fabric, constitutively involving social institutions, social expectations, shared vocabularies, etc. Hence, all sociological communications must account for their being communicated within society' Although this may seem obvious, we feel that many social theories do not recognizà this axiom and talk about society as if their own theoretical [1] Michael Schiltz, Deparrment of Oriental Studies. Faculty of Arts, Catholic University Leuven, Blijde Inkomsstraat 21, 3000 Leuven, Betgium, e-mail: Michael.Schiltz@arts'kuleuven ac'be GeÍ Verschraegen, Deparrment of Sociology, Faculty of Social Sciences, Catholic University Leuven, E. Van Evenstràat2b,j000 L.ur.n, Belgium, email: Gert.Verschraegen@soc.kuleuven.ac.be