This collective work provides a chronological and up-to-date reconstruction of the three-round debate between Robert Alexy and Ralf Poscher.The debate represents the German development of an enduring jurisprudential controversy over the concept and adjudicatory role of legal principles, classically addressed by HLA Hart and Ronald Dworkin. Alexy's principles theory, which has initially defined 'legal principles' as optimisation requirements, currently argues that t...

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. In borderline cases, the law seems t...