The APA thus codifies for agency cases the unremarkable, yet elemental proposition reflected by judicial practice dating back to Marbury: that courts decide legal questions by applying their own judgment. It specifies that courts, not agencies, will decide “all relevant questions of law” arising on review of agency action, §706 (emphasis added)— even those involving ambiguous laws—and set aside any such action inconsistent with the law as they interpret it. And it prescribes no deferential standard for courts to employ in answering those legal questions. That omission is telling, because Section 706 does mandate that judicial review of agency policymaking and factfinding be deferential. See §706(2)(A) (agency action to be set aside if “arbitrary, capricious, [or] an abuse of discretion”); §706(2)(E) (agency factfinding in formal proceedings to be set aside if “unsupported by substantial evidence”).
In a statute designed to “serve as the fundamental charter of the administrative state,” Kisor v. Wilkie, 588 U. S. 558, 580 (2019) (plurality opinion) (internal quotation marks omitted), Congress surely would have articulated a similarly deferential standard applicable to questions of law had it intended to depart from the settled pre-APA understanding that deciding such questions was “exclusively a judicial function,” American Trucking Assns., 310 U. S., at 544. But nothing in the APA hints at such a dramatic departure. On the contrary, by directing courts to “interpret constitutional and statutory provisions” without differentiating between the two, Section 706 makes clear that agency interpretations of statutes—like agency interpretations of the Constitution—are not entitled to deference. Under the APA, it thus “remains the responsibility of the court to decide whether the law means what the agency says.” Perez v. Mortgage Bankers Assn., 575 U. S. 92, 109 (2015) (Scalia, J., concurring in judgment).
The text of the APA means what it says.