Proportionality in International Law

Across a broad range of subjects, there is now wide agreement that the principle of proportionality governs the extent to which a provocation may lawfully be countered by what might otherwise be an unlawful response. That is the central role assigned to proportionality in international law and it is deeply rooted in the cultural history of societies. However, if the core institutions of a legal system are too weak to be relied upon to take remedial action against wrongdoers, then they must at least be authorized to license appropriate action by the wronged party and to insure that its response remains within prescribed parameters.The practice described in this essay demonstrates that a high degree of accord is emerging across a broad range of issues to the appropriate standards by which the proportionality of countermeasures can be assessed. The practice of various institutions authorized to render second opinions as to the compliance with those standards is gradually narrowing the range of indeterminacy inherent in the term proportionality. Some of this case law has been disappointingly episodic. The well-crafted second opinion, through its precision, its invocation of precedent, and its careful weighing of the probity of the facts presented to it, deepens and narrows the jurisprudential stream while strengthening its embankments.If applied in practice through second opinions rendered by legitimate institutions, proportionality is an example of an indeterminate principle becoming gradually empowered to provide persuasive answers to difficult questions and, thereby, case by case, building the objective determinacy of the principle.