Kagan calls the majority decision that executive “agencies have no special competence” [to interpret ambiguous legislation] malarkey. She says it is the courts that lack the expertise and experience and assigned work scope for dealing with political ambiguities.

The majority makes two points in reply, neither convincing. First, it insists that “agencies have no special competence” in filling gaps or resolving ambiguities in regulatory statutes; rather, “[c]ourts do.” Ante, at 23. Score one for self-confidence; maybe not so high for self-reflection or -knowledge. Of course courts often construe legal texts, hopefully well. And Chevron’s first step takes full advantage of that talent: There, a court tries to divine what Congress meant, even in the most complicated or abstruse statutory schemes. The deference comes in only if the court cannot do so if the court must admit that standard legal tools will not avail to fill a statutory silence or give content to an ambiguous term . That is when the issues look like the ones I started off with: When does an alpha amino acid polymer qualify as a “protein”? How distinct is “distinct” for squirrel populations? What size “geographic area” will ensure appropriate hospital reimbursement? As between two equally feasible understandings of “stationary source,” should one choose the one more protective of the environment or the one more favorable to economic growth? The idea that courts have “special competence” in deciding such questions whereas agencies have “no[ne]” is, if I may say, malarkey. Answering those questions right does not mainly demand the interpretive skills courts possess. Instead, it demands one or more of: subject-matter expertise, long engagement with a regulatory scheme, and policy choice. It is courts (not agencies) that “have no special competence”–or even legitimacy–when those are the things a decision calls for.