A Reason-Based Approach to Coherence in Customary International Law

This paper focuses on customary international law (CIL) to point out some limitations of a deductive-syllogistic style of reasoning. It emphasises two CIL complexities. First, even well-established CIL rules are known to have exceptions, but that does not call for the conclusion that a CIL rule is non-existent. Second, the preceding practice for recognising a CIL rule does not need to be uniform. If one attempts to explain such complexities employing a syllogism-oriented, deductive style of reasoning, one will face severe difficulties and mismatches between the law and the model in place. While deductivism ties coherence to the absence of contradiction, legal reasoning allows coherence to find its way out of contradiction. As an alternative to the deductive model, this paper argues that reason-based logic (RBL) provides a suitable framework for understanding the law and CIL complexities. This logic is reason-based because it gives the centre stage to reasons instead of syllogisms, allowing one to balance reasons in favour and against a conclusion. This paper is structured as follows: Section 1 focuses on the two abovementioned CIL complexities. Section 2 examines deductivism and points out why it is unable to account for such complexities. Section 3 introduces the reasonbased alternative. Section 4 concludes the paper.