A MODEL OF JURIDICAL ACTS Jaap Hage 1 ABSTRACT This papers belongs to a project that deals with juridical acts, powers and competences. It is primarily meant for a readership with an interest in implementing juridical acts in a knowledge-based system, but only the final part of the paper is technical. Most of the paper is devoted to creating an understanding of what goes on when the law makes it possible to intentionally create or modify legal facts. To this purpose, there is special attention for the concept of a juridical acts and for the different kinds of rules which make it possible to change the ‘world of law’ by means of intentional acts. Keywords Avoidance, competence, institutional facts, powers, (kinds of) rules 1 Introduction In law, juridical acts (legal acts, legal transactions, acts-in-the-law, Rechtsgeschäfte, actes juridiques) play a central role. The concept of a juridical act applies to phenomena in different legal systems, even in systems where the expression ‘juridical act’ is not part and parcel of every lawyer’s conceptual tool kit. Juridical acts, such as contracting, or terminating a contract, making a last will, transferring a property right, making a statute, granting a license, and passing a verdict, are familiar phenomena in the law of both the common law and the civilian tradition. In the civilian tradition it is customary to treat all these different events under the common denominator of juridical acts. Expressions used to denote them are ‘juridical acts’ (Von Bar 2009, 183), ‘Rechtsgeschäfte’(Larenz and Wolf 2004, 393) and ‘actes juridiques’ (Terré 2006, 170). In the common law tradition, the notion of a juridical act does not play the central role which it has in the civilian tradition, but a similar role is taken by the notion of a power. Where the civilian tradition speaks of a juridical act, the common law tradition speaks of the exercise of a power (Halpin 1996). As a first approximation, juridical acts may be characterized as intentional changes in ‘the world of law’, where the world of law is the set of all facts and things brought about by the law. (This will be made more precise in section 4.) Although quite a bit work in AI and Law more or less touches upon juridical acts (e.g. Hage and Verheij 1999; Hage 2005b; Andrade 2007; Dahiyat 2007; Sartor 2005, chapters. 21-25, 2006, 2009 a and b), a systematic treatment of this central legal notion from 1 The author thanks Torben Spaak and the anonymous reviewers for Artificial Intelligence and Law for their useful comments on the draft version of this paper. The usual disclaimer applies.