Expressio Unius
Expressio unius est exclusio alterius — "the expression of one thing is the exclusion of the other" — is a canon of statutory construction holding that when a legal text specifically enumerates certain items, items not mentioned are presumed excluded. In HTSUS classification, this principle gives force to enumerative chapter and section notes: a list of excluded goods excludes exactly those goods, and similar goods not listed remain subject to normal classification.
In Detail
The maxim is a standard tool of statutory interpretation in U.S. courts, including the Court of International Trade and the Court of Appeals for the Federal Circuit. Its application is not mechanical — courts consider whether the drafter's evident purpose was to create an exhaustive list or merely an illustrative one. The presence of terms like "including" or "such as" signals an illustrative, non-exhaustive list; their absence in an enumerative context signals exhaustiveness. In the HTSUS, note drafters are deliberate, and enumerative lists in chapter and section notes are generally read as exhaustive.
In the HTSUS, expressio unius most commonly applies to exclusionary notes that list specific goods excluded from a chapter or heading. If Chapter 84 Note 1 excludes "articles of Chapter 85," the exclusion is specific to that chapter — articles of Chapter 86 are not excluded by that note, even if they might be analogous. Conversely, an inclusionary note listing specific goods does not automatically include goods not listed, even similar ones. The enumeration is the boundary.
The maxim also operates at the heading level. An eo nomine heading that specifically names certain goods implicitly excludes similar goods not named — a heading for "ball bearings" does not cover roller bearings by inference. This is expressio unius working alongside lex specialis: the specific enumeration controls, and what is not enumerated is not covered. The interaction between these canons is why the precise language of headings and notes is treated as definitive, not merely illustrative.
Classification Significance
Expressio unius determines the boundaries of note-based exclusions and inclusions, which govern GRI 1 analysis. Misreading an enumerative list as non-exhaustive — concluding that a note's exclusion extends beyond its listed items by analogy — is a classification error that CBP audits routinely catch. The canon is also invoked in CBP protests and CIT appeals when the scope of a chapter note exclusion is disputed. Understanding it precisely is essential for defensible classification documentation.
How Kanon Handles This
Kanon's corpus parser captures chapter and section notes in structured condition trees, and the classification engine treats enumerated lists in exclusionary notes as exhaustive — applying expressio unius to determine precisely which products a note affects and which it does not. The boundaries of each note's application are documented in the Classification Support Package as part of the GRI 1 analysis.