The majority in King v. Burwell surprised many observers by declining to grant Chevron deference to the IRS interpretation of the Affordable Care Act at issue. Instead, the Chief Justice’s opinion held thatChevron does not apply to questions that are of “deep economic and political significance.”

This post does not analyze how this decision relates to Court precedents on the scope of Chevron, a topic will surely attract significant commentary. This post explores a different question: why is the Court’s application of deference regimes like Chevron so varied and unpredictable? I analyze this question in greater depth in a paper with Professor Bill Eskridge.

One answer, which has some empirical support, is that the justices, like most people, value case outcomes over methodologies such as deference doctrine. Put differently, interest in the legal or policy issues at stake in the particular case at hand overpower concern over being consistent with respect to deference doctrine. The result is an unclear body of case law. This explanation does not appear to work for King v. Burwell, as the case outcome would have been the same had the Court appliedChevron deference.

A related explanation is that the cost to the justices (and to the Court itself) of diverging from precedent on deference is lower than for substantive issues. Because people care less about abstract methodological issues like deference, diverging from precedent attracts less attention. Furthermore, methodological issues like deference less directly implicate reliance interests, an important rationale for adhering to precedent. Again, this explanation does not appear to work for King v. Burwell because applying Chevron would not have altered the outcome.

Another explanation is that justices take a larger strategic view of the Court’s position in the separation of powers system, preferring a deference regime that will best achieve their goals (whether legal or policy) over the long term. Under this view, one might argue that conservative justices have become less enthusiastic about Chevron deference under a Democratic president and Republican Congress. Perhaps this explains why the Chief Justice sought to restrict Chevron in this and other recent cases. But it does not explain why all four of the more liberal justices signed onto the Chief’s Justice’s opinion without writing separately on Chevron.

Finally, perhaps all of this is the product of sincerely held but complicated (and evolving) preferences among the justices over deference doctrine itself. But, this is difficult to test.

In short, none of these explanations is fully satisfactory. Perhaps the answer will become clearer as the doctrine evolves over, but I’m not optimistic after looking back at 31 years of muddled cases onChevron’s scope.