In Dubio Mitius

Merkouris, P., 11-Dec-2018, Between the Lines of the Vienna Convention?: Canons and Other Principles of Interpretation in Public International Law. Klingler, J., Parkhomenko, Y. & Salonidis, C. (eds.). Alphen aan den Rijn: Wolters Kluwer, p. 259-306 48 p.

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Latin terms have always been an indispensable tool in the arsenal of any ‘user’ of international law, be they a practitioner, a judge, academic or anyone else who dabbles in the mercurial waters of the international legal system. That is not surprising, as the employment of such terms serves simultaneously two functions. First, it pays homage to the Roman roots of many legal systems, since it was the Roman legal system that was the first to approach the study of law both systematically and systemically. Second, and perhaps more pragmatically, it shrouds the relevant notion with a penumbra of authority. If it is in Latin it must be a principle of binding force with a long tradition of use and of great authoritative value.

Interpretation in international law is no stranger to this approach. Principles such as contra proferentem, pari materia, in dubio mitius, favor debitoris, exceptio est strictissimae applicationis, semper autem in fide quid senseris non quid dixeris cogitandum, and many others too numerous to mention find their way in judgments of international courts and tribunals with notable frequency. Although these principles are not mentioned explicitly in the Vienna Convention on the Law of Treaties (VCLT) that does not automatically imply that they may not form either part of the VCLT interpretation system or of customary international law.

In this Chapter the focus will be on the in dubio mitius principle, often also referred to as restrictive interpretation. First, what we will examine is the history of that principle. Was it always stated as such from the very start or can we trace it back to other principles of Roman law, which were later transmutated into what we recognize today as in dubio mitius? This part of analysis will not only focus only on the origins of the principle in domestic legal systems but will also trace out the origins of the principle in various draft codes on the law of treaties and in the discussions of the Institut de Droit International and the International Law Commission (ILC), when they dealt with the issue of interpretation of treaties during the 50s and 60s. This historical overview will allow us to clarify the key concepts surrounding this principle and also the reasons for it being conspicuous by its absence in the final version of the VCLT text.

However, such an analysis although a good starting point can only take us so far. It is for this reason that the kernels found during the historical overview will be put under the microscope and cross-checked with actual judicial practice throughout the ages and from various international courts and tribunals irrespective of their subject-matter jurisdiction. In this manner, trends in the understanding and employment of the in dubio mitius principle will be identified, as well as any, if at all, relevance for the international legal system as a whole, or for a particular area of international law. Three are the key axes around which the analysis will revolve. First, what the inherent precepts and paradoxes of the notion of in dubio mitius are. Second, whether the in dubio mitius principle has any particular relevance or customary status for a specific area of international law, or for a specific type of treaties and/or provisions. Finally and on the basis of all the aforementioned, what the place of in dubio mitius is in relation to other principles, and more importantly in relation to the interpretative process set out in the VCLT.

All the above considerations will gradually peel off layer by layer all uncertainties, until we reach the nucleus of the binding or not nature of this principle and its apposite place in the interpretative process of the international legal system.
Original languageEnglish
Title of host publicationBetween the Lines of the Vienna Convention?
Subtitle of host publicationCanons and Other Principles of Interpretation in Public International Law
EditorsJoseph Klingler, Yuri Parkhomenko, Constantinos Salonidis
Place of PublicationAlphen aan den Rijn
PublisherWolters Kluwer
Number of pages48
ISBN (Print)9789041184030
Publication statusPublished - 11-Dec-2018


  • in dubio mitius, interpretation, construction, canons of construction, restrictive interpretation, interpretation of treaties, interpretation of customary international law, customary international law, Vienna Convention on the Law of Treaties, VCLT

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