Vague expressions are omnipresent in natural language. As such, their use in legal texts is virtually inevitable. If a law contains vague terms, the question whether it applies to a particular case often lacks a clear answer. One of the fundamental pillars of the rule of law is legal certainty. The determinacy of the law enables people to use it as a guide and places judges in the position to decide impartially. Vagueness poses a threat to these ideals. Inborderline cases, the law seems to be indeterminate and thus incapable of serving its core rule of law value.In the philosophy of language, vagueness has become one of the hottest topicsof the last two decades. Linguists and philosophers have investigated what distinguishes "soritical " vagueness from other kinds of linguistic indeterminacy, such as ambiguity, generality, open texture, and family resemblance concepts. There is a vast literature that discusses the logical, semantic, pragmatic, and epistemic aspects of these phenomena. Legal theory has hitherto paid little attention to the differences between the various kinds of linguistic indeterminacy that are grouped underthe heading of "vagueness ", let alone to the various theories that try to account for these phenomena.Bringing together leading scholars working on the topic of vagueness inphilosophy and in law, this book fosters a dialogue between philosophers and legal scholars by examining how philosophers conceive vagueness in law from their theoretical perspective and how legal theorists make use of philosophical theories of vagueness. The chapters of the book are organized into three parts. The first part addresses the import of different theories of vagueness for the law, referring to a wide range of theories from supervaluationist to contextualist and semantic realistaccounts in order to address the question of whether the law can learn from engaging with philosophical discussions of vagueness. The second part of the book examines different vagueness phenomena. Thecontributions in part 2 suggest that the greater awareness to different vagueness phenomena can make lawyers aware of specific issues and solutions so far overlooked. The third part deals with the pragmatic aspects of vagueness in law, providing answers to the question of how to deal with vagueness in law and with the professional, political, moral, and ethical issues such vagueness gives rise to.

Prof. Dr. Ralf Poscher is Professor of Public Law and Legal Philosophy at Albert-Ludwigs-University of Freiburg and managing director of the Centre for Security and Society of the University of Freiburg. Prof. Poscher has been a Fernand Braudel Senior Fellow at the European University Institute in Florence (2013), a guest researcher of the "Program in Law and Public Affairs" at Princeton University (2012), a member of the Institute for Advanced Study in Princeton,USA (2007-2008), and a visiting professor at the University of Osaka (2007). His areas of research cover legal theory, fundamental rights and national security law.Geert Keil is Professor of Philosophy at Humboldt University of Berlin. His main areas of research are the philosophy of mind and action, epistemology, philosophical anthropology and metaphysics. Awarded with a Heisenberg scholarship of the German Research Foundation (DFG) and a Feodor Lynen scholarship of the Alexander von Humboldt Foundation, he researched at the Universities of Trondheim, Stanford, and Basel. From 2005 to 2010 he held a chair in theoretical philosophy at RWTH AachenUniversity.