I know that not everyone reads the comments, so I thought I'd pull something out of the comments on a previous post by Marc Benitah on the Kosovo ICJ decision. In our brief back and forth there, Marc pointed me to a statement by Judge Simma in his separate opinion in that case:
... the Court could have explored whether international law can be deliberately neutral or silent on a certain issue, and whether it allows for the concept of toleration, something which breaks from the binary understanding of permission/prohibition and which allows for a range of non-prohibited options. That an act might be “tolerated” would not necessarily mean that it is “legal”, but rather that it is “not illegal”.
See para. 9.
With regard to all things related to international law, I like to start with my usual caveat that I don't know all that much about international law. But in reading the Judge Simma quote, I was struck by the possible parallel to AD Agreement Article 17.6(ii). The second sentence of that provision says:
Where the panel finds that a relevant provision of the Agreement admits of more than one permissible interpretation, the panel shall find the authorities' measure to be in conformity with the Agreement if it rests upon one of those permissible interpretations.
Article 17.6(ii) is sometimes analogized to a deferential standard of review in the U.S. administrative law context, but maybe it has a counterpart in this kind of thinking about international law as well? Could the "range of non-prohibited options" be similar in effect to "more than one permissible interpretation"? I know the U.S. is skeptical of giving too great a role to international law in WTO dispute settlement (see, e.g., here), but I wonder if this could be a useful argument for it to make in support of "zeroing" being allowed.
(I should clarify that I don't necessarily support either the permissibility of zeroing or the use of international law in WTO dispute settlement. Just thinking out loud here!)
