It is not meaningful to speak of a “correct” method of legal interpretation on the plausible “impotency assumption” that agents cannot reliably adjust the range of interpretive methods that is sociologically legitimate in any given society at any given time. Whether a method of legal interpretation is correct essentially depends, in part, on the effect its use will have on the legal system as a whole. But, on the impotency assumption, it is Quixotic to think that a given use of the “correct” method of interpretation will improve the legal system. Further, any improvement will be de minimis.
(1) De minimis. If nobody can affect the range of interpretive methods that it is sociologically legitimate for a particular judge to deploy at any given time then the law is not going to be more or less “pure” depending on which of these methodologies that judge employs. Purity is systematic. The law as a whole can be more or less pure. Subsystems of law can be more or less pure. But a decision can never be. Ad hoc purity is thus an oxymoron. As it is all that can be guaranteed by one judge using the correct interpretive methodology – and as that is all that can be guaranteed on a plausible cashing out of the impotency assumption – the incrementation toward purity thereby brought about is therefore de minimis. Thus, the mere fact that a given methodology is the “right” one does not give a judge reason to deploy it* – ex hypothesi, his legal system isn’t going to be any better for his doing so. This means that to select among competing sociologically legitimate methodologies a judge might as well directly recur to other, non-methodological, values.
(2) Quixotic. Judicial decisions are not isolated phenomena – they interact with future decisions and impact on the law in multiple different ways. To use the “correct” interpretive methodology in a situation where multiple methodologies are sociologically legitimate is therefore not only to effect a de minimis improvement in the law, but also Quixotic; subsequent judges will undo what you have done, but what you have done is only valuable if they won’t undo it. (This is because fidelity to the correct interpretive method is meant to promote the virtues of a legal system, not the pre-legally best result in every case.)
* I put “right” in scare quotes because my argument, if successful, actually implies that there is no such thing as a “right” methodology.