International lawyers seek to demonstrate that their discipline is scientific; that is, committed to values including rationality, progress and objectivity.42 43 But what is reasonable depends on the circumstances.44Reasonableness is assessed according to the special features of a case.45 It is not a benchmark capable of precise definition or mechanical application. But reasonableness ‘is often a false friend that gives the impression of an objective threshold where none exists’.46 Although it provides flexibility for a court, the concept is vague and offers little clear or practical guidance to decision makers. Reasonableness moreover implies that the standard does not remain fixed. It requires a highly fact-specific inquiry.
42A Orford, ‘Scientific Reason and the Discipline of International Law’ (2014) 25 EJIL 369.
44ICJ, Advisory Opinion on the Interpretation of the Agreement of 25 March 1951 between the World Health Organisation and Egypt  ICJ Rep 96.
45Wemhoff v Germany App no 2122/64 (ECtHR, 1968) Ser A, No 7, para 10.
46The Government of Sudan/The Sudan People’s Liberation Movement/Army (Abyei Arbitration), Award of the Arbitral Tribunal of 22 July 2009, Dissenting Opinion of Judge Al-Khasawneh, para 182.