Yesterday, the Court decided Esquivel-Quintana v. Sessions, an immigration case implicating Chevron. Under Chevron, of course, courts and agencies are bound by unambiguous statutes. But if a statute is ambiguous, courts must defer to reasonable interpretations of that statute rendered by the agency charged with interpreting that statute.   One issue underlying Chevron is identifying what determines whether a statute is unambiguous. That was one of the questions in Esquivel-Quintana.

At issue in the case were several provisions of the Immigration and Nationality Act authorizing the removal of an alien convicted of a state-law felony for “sexual abuse of a minor.” Esquivel-Quintana was convicted of violating California’s statutory rape law. That law makes it a crime for a person to have sexual intercourse with a “minor” who is more than three years younger than the perpetrator, and it defines “minor” as a person under 18. The Board of Immigration Appeals held that Esquivel-Quintana’s conviction provided a basis for removal.

The Supreme Court reversed. It refused to defer to the Board’s interpretation, concluding that the Immigration Act unambiguously defined minor as a person younger than 16. But here’s the thing. The text of the Immigration Act does not define minor. Nor does minor have a single, commonly accepted definition. Sometimes it refers to someone under 21 (drinking), other times to someone under 18 (most things), and still other times other times to someone under 16 (driving). So to support its conclusion that the Act unambiguously defines minor as under 16, the Court pointed to dictionary definitions, state laws, and other federal acts defining minor.

As others have noted, it’s hard to say that those materials unambiguously establish that the Immigration Act defines minor as younger than 16. Consistent with the different uses I just mentioned, dictionaries do not uniformly define minor as under 16. Nor do state laws. And although it is true that other federal statutes define minor as under 16, the absence of a comparable definition (or a cross reference to those other statutes) in the Immigration Act arguably suggests that it does not adopt the same definition.   These ambiguities suggest that the Act does not firmly establish a minor as under 16.

But another important point is that the Court’s approach shifts the line between Chevron’s step 1 and step 2.  Dictionaries are a fair way to ascertain a word’s meaning because their function is to define words. But state laws and other federal laws are another story. Their function is to regulate, not provide definitions.   They can provide insights into meanings of words used in other statutes, but that is only incidental. It is for this reason that courts turn to other statutes when interpreting a statute that is unclear on its face. Those other statutes are just circumstantial evidence of meaning—just like legislative history, the social events giving rise to the enactment of a statute, and the countless other things courts look at when interpreting ambiguous statutes. By claiming that those other statutes can establish unambiguity, Esquivel-Quintana shifted the role of other statutes from Chevron step 2 to Chevron step 1.

Maybe the Court meant in Esquivel-Quintana to make another inroad on Chevron. But if we accept Chevron and its premise that agencies have the primary authority to interpret statutes, agencies should not be forced to dig through the federal and state code books when rendering their interpretations. Their job is to implement policies that are consistent with the text of the statute, not to try to uncover Congress’s intent through archaeology. Permitting a court to determine that a law is unambiguous based on other state and federal laws impairs the ability of agencies to accomplish that task.