This study considers State silence which may entail acquiescence and can thus contribute inter alia to the formation of historic rights, the identification of customary international law, and the interpretation of treaties over time. Relying on the historical understanding of acquiescence in British and francophone literature, it argues that there are probability and normative justifications for establishing acquiescence as a ‘presumption of acceptance’ in international law, and that these considerations have influenced the modern international law understanding of acquiescence as an exceptional occurrence subject to stringent qualifications.