Jaap Hage graduated in both law and philosophy at the University of Leiden, and defended there his doctoral thesis about the normative meaning of facts. Then he redirected his research to Artificial Intelligence and Law, and in particular the logic of (defeasible) legal reasoning. On this topic he published numerous articles and two monographs (1997: Reasoning with Rules; 2005: Studies in Legal Logic). Meanwhile he had left Leiden for Maastricht University, where he became the chair holder for Jurisprudence. His main topic of research became the basic concepts of law, and the grounding of law in social reality. On these topics he also published numerous articles, co-edited a collection of articles (2009: Concepts in Law) and published a monograph (2018: Foundations and Building Blocks of Law). Recently his research interest has moved to the relation between law and the cognitive sciences.