Here's an excerpt from the majority opinion in the recent Loper Bright U.S. Supreme Court decision that puts an end to Chevron deference, in which the majority says that it does not make sense to talk about "permissible" interpretations because there is always a "single, best" interpretation:
Courts, after all, routinely confront statutory ambiguities in cases having nothing to do with Chevron—cases that do not involve agency interpretations or delegations of authority. Of course, when faced with a statutory ambiguity in such a case, the ambiguity is not a delegation to anybody, and a court is not somehow relieved of its obligation to independently interpret the statute. Courts in that situation do not throw up their hands because “Congress’s instructions have” supposedly “run out,” leaving a statutory “gap.” Post, at 2 (opinion of KAGAN, J.). Courts instead understand that such statutes, no matter how impenetrable, do—in fact, must—have a single, best meaning. That is the whole point of having written statutes; “every statute’s meaning is fixed at the time of enactment.” Wisconsin Central Ltd. v. United States, 585 U. S. 274, 284 (2018) (emphasis deleted). So instead of declaring a particular party’s reading “permissible” in such a case, courts use every tool at their disposal to determine the best reading of the statute and resolve the ambiguity.
In an agency case as in any other, though, even if some judges might (or might not) consider the statute ambiguous, there is a best reading all the same—“the reading the court would have reached” if no agency were involved. Chevron, 467 U. S., at 843, n. 11. It therefore makes no sense to speak of a “permissible” interpretation that is not the one the court, after applying all relevant interpretive tools, concludes is best. In the business of statutory interpretation, if it is not the best, it is not permissible.
In the WTO law context, we are all familiar with the idea of permissible interpretations as set out in AD Agreement Article 17.6(ii):
In examining the matter referred to in paragraph 5:
...
(ii) the panel shall interpret the relevant provisions of the Agreement in accordance with customary rules of interpretation of public international law. 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.
In Colombia - Frozen Fries, the MPIA arbitrators, when discussing Article 17.6(ii), emphasized the possibility of there being multiple permissible interpretations, rather than having to reach a single "final" or "correct" interpretation in every case:
4.13. Reading these provisions together, we aim to integrate the elements of interpretation under Article 17.6(ii). As a result, we will begin by asking ourselves whether Colombia's proposed interpretation of the phrase "where appropriate" in Article 5.2(iii) – reflected in MINCIT's decision to initiate its investigation, in part, on the basis of third-country sales prices – is a "permissible" one. As a yardstick for "permissibility", the first sentence of Article 17.6(ii) refers us to the customary rules of treaty interpretation. However, we will not engage in our own, de novo interpretation of the terms "where appropriate" so as to arrive at what we consider to be the "final" or "correct" application of Articles 31 and 32 of the Vienna Convention. Instead, we will ask whether a treaty interpreter, using the method for treaty interpretation set out in the Vienna Convention – that is, an interpretation "in good faith in accordance with the ordinary meaning to be given to the terms of the treaty in their context and in the light of its object and purpose" and, where appropriate, "supplementary means of interpretation" – could have reached Colombia's interpretation. And this even though we, as de novo treaty interpreters, might have reached a different conclusion.
4.14. Our approach assumes, as the second sentence does, that different treaty interpreters applying the same tools of the Vienna Convention may, in good faith and with solid arguments in support, reach different conclusions on the "correct" interpretation of a treaty provision.43 This may be particularly true for the Anti-Dumping Agreement, which was drafted with the understanding that investigating authorities employ different methodologies and approaches. Treaty interpretation is not an exact science and applying the Vienna Convention's method does not magically and inevitably lead to a single result. In most cases, treaty interpretation involves weighing, balancing, and choice.
4.15. Thus, the ultimate question for us when testing a proposed interpretation is to draw a line beyond which an interpretation is no longer "permissible" under the Vienna Convention method for treaty interpretation. Dictionary meanings support the idea that the search for "permissible" interpretations differs from an attempt to find one's own – "final" and "correct" – interpretation.44 Rather, the question is whether someone else's interpretation is "permitted", "allowable", "acceptable", or "admissible" as an outcome resulting from a proper application of the interpretative process called for under the Vienna Convention. Obviously, not just any interpretation put forward by an authority can be accepted as "permissible". The interpretative process under the Vienna Convention sets out an outer range beyond which meanings cannot be accepted. Just as permissible interpretations cannot be limited to a single "final" and "correct" answer as determined by a given tribunal, not all interpretations have the required degree of solidness or analytical support for them to be given deference as "permissible" within the bounds of the Vienna Convention method for treaty interpretation.
The approach set out by the MPIA above can be distinguished from earlier WTO decisions that seemed wary of a standard that was open to multiple permissible interpretations.
(Jackson and Croley laid out the connection between Chevron and the Article 17.6(ii) standard here).
I'm not sure I understand the reluctance to accept that statutes or treaties may be vague or ambiguous enough that there are multiple permissible interpretations. In some instances, the choice between one interpretation or another is a very close call. If a court is considering multiple interpretations, and one is slightly better than another (say, 55% to 45%, to put concrete figures on this), I'm not convinced that declaring the 55% interpretation to be the "best" one, which therefore must be followed, is always the right approach. At some degree of uncertainty about which interpretation is best, I would have no problem saying, in the circumstance where an agency is crafting an implementing regulation based on its interpretation of the statute, that there are multiple permissible interpretations.
Of course, if you do adopt a "best" interpretation approach, the statute or treaty drafters can step in to correct the interpretation if they don't like how the court came out. But in practice, that's often difficult for practical political reasons, and the court's interpretation is likely to govern. It's worth noting in this context that there are policy implications from these interpretive choices, and we should think about which government actors are best placed to take responsibility for these policy decisions.
I suspect that many people will consider this suggestion to be a bit off the wall, but to deal with the political and policy-making concerns, I would be interested in thinking about a process through which courts could say to the legislators/treaty drafters something to the effect of: "We're not sure what you meant with regard to how this ambiguous provision should be interpreted in the context at hand. Could you please clarify?" I haven't given any deep thought to how this might work in practice, but perhaps something along the lines of this, this, this, or this in the U.S. domestic context.
