Interpretation Canons

Expressio unius est exclusio alterius means the expression of one thing excludes others. In HTSUS classification, it makes chapter note lists exhaustive: items specifically named as excluded are excluded; items not named remain classified normally.

Lex specialis is the legal maxim that a specific provision controls over a general one. In HTSUS classification, it underlies why chapter notes override section notes, specific headings beat general headings, and GRI 3(a) awards classification to the more specific description.

Mutatis mutandis means "with the necessary changes having been made." In HTSUS classification, GRI 6 applies GRIs 1–5 to subheadings mutatis mutandis — the same rules govern, adapted to operate at the subheading level.

Noscitur a sociis means "a word is known by the company it keeps." In HTSUS classification, it guides interpretation of ambiguous heading terms by reference to the surrounding terms in the same provision — CBP and CIT cite it regularly in scope disputes.