Expressio unius est exclusio alterius is a canon of statutory and contract interpretation meaning “the expression of one thing is the exclusion of another.” When a statute or agreement lists specific items, courts presume that anything left off the list was left off on purpose. It is a presumption, not a rule, and its strength depends entirely on whether the list looks deliberate or merely illustrative.
What the Canon Actually Does
The reasoning is simple. If a drafter took the trouble to name particular things, a court should respect that choice rather than add items on its own. The more detailed and careful the list, the stronger the inference that omissions were intentional.
The Supreme Court leaned on this logic in Russello v. United States (1983). One subsection of the RICO forfeiture statute reached “any interest” a defendant acquired through racketeering; the very next subsection narrowed its reach to interests “in any enterprise.” The Court held the mismatch was intentional. Congress used broad language in one place and narrow language next door, and if it had wanted both subsections to be narrow, it would have written them that way.1Justia U.S. Supreme Court Center. Russello v. United States, 464 U.S. 16 (1983)
The Ninth Circuit applied the same logic in Silvers v. Sony Pictures Entertainment, Inc. (2005). Federal copyright law spells out who may sue for infringement. Because Congress had specified the list of proper plaintiffs, the en banc court held that assignees of bare infringement claims, who did not hold the underlying copyright, were excluded from bringing suit.2Justia Law. Silvers v. Sony Pictures Entertainment Inc., 402 F.3d 881 (9th Cir. 2005)
In both cases the specificity itself did the work. A statute that names three vehicles subject to inspection invites the inference that a fourth was left out on purpose.
When Courts Reject the Canon
The presumption breaks down when the omission looks accidental or when the list was never meant to be complete. In Barnhart v. Peabody Coal Co. (2003), the Supreme Court refused to treat two listed exceptions in the Coal Industry Retiree Health Benefit Act as implying the exclusion of a third scenario Congress had not anticipated. As the Court put it, “the enunciation of two exceptions does not imply the exclusion of a third when there is no reason to think that Congress considered such an exclusion.”3Cornell Law Institute. Barnhart v. Peabody Coal Co.
In United States v. Vonn, the Court declined to apply the canon mechanically to Federal Rule of Criminal Procedure 11. The presence of a harmless-error standard in one part of the rule did not, on its own, exclude the plain-error standard found elsewhere in the rules. History and purpose controlled instead.4Cornell Law Institute. United States v. Vonn
Certain textual signals defeat the canon almost automatically:
- “Including” or “such as” tells the reader the items are examples, not boundaries.
- “At a minimum” signals a floor with room above it.
- Catch-all phrases like “or other similar conduct” tell the court the drafter wanted flexibility beyond the named items.
The canon works when a list looks designed to be complete. When context suggests the drafter was giving examples, courts set it aside.
How It Interacts With Other Canons
Expressio unius rarely operates alone. Its most common companion is ejusdem generis, “of the same kind.” When a statute lists specific items followed by a general term, such as “cars, trucks, buses, and other vehicles,” ejusdem generis limits the general term to things similar to the specific ones listed. A court might read “other vehicles” to include vans but not bicycles. That softens expressio unius: instead of excluding unnamed items entirely, the general term creates a category that captures similar ones the drafter did not spell out.
Noscitur a sociis, “a word is known by the company it keeps,” uses surrounding words to clarify an ambiguous term within a list. If a statute regulates “banks, savings institutions, and credit unions,” a court reading “savings institutions” would look to the neighbors and conclude the statute targets consumer deposit-taking entities. This canon can either confirm that a list has a bounded purpose or reveal that the listed terms share a meaning broad enough to reach items not named.
The rule against surplusage also shapes the analysis. Courts assume every word in a statute carries independent meaning. If treating an unlisted item as included would make one of the listed terms redundant, that pushes toward exclusion. This is where expressio unius draws its strongest support: a legislature would not have bothered listing specific items if it meant the provision to reach everything.
Why the Canon Matters More After Loper Bright
Under Chevron U.S.A., Inc. v. Natural Resources Defense Council, courts confronting ambiguous statutes often deferred to the administering agency’s interpretation as long as it was “permissible.” That framework blunted textual canons. Even if expressio unius pointed one way, an agency’s reading could survive if it fell within a zone of reasonable interpretation.
The Supreme Court’s 2024 decision in Loper Bright Enterprises v. Raimondo overruled Chevron. Courts must now exercise “independent judgment in deciding whether an agency has acted within its statutory authority” and use “traditional tools of statutory construction” to find the best reading of the statute, not merely a permissible one.5Supreme Court of the United States. Loper Bright Enterprises v. Raimondo
The underlying dispute showed why the shift matters for expressio unius. Congress had expressly authorized industry-funded onboard observers for certain fisheries and for foreign vessels, but said nothing about the Atlantic herring fishery. A dissenting judge below argued that this silence, read against the express provisions elsewhere, “unambiguously indicated that NMFS lacked the authority” — a textbook expressio unius argument.5Supreme Court of the United States. Loper Bright Enterprises v. Raimondo Under old Chevron deference, an argument like that could lose at step two. Without Chevron, it lands with full force.
The practical result: litigants challenging agency action have stronger footing to argue that congressional silence reflects intentional exclusion rather than an ambiguity for the agency to fill. Agencies face more pressure to ground their authority in explicit statutory text.
Expressio Unius in Contracts
The canon applies with equal force to private agreements. When a contract lists specific rights, obligations, or triggering events, courts generally treat unlisted items as excluded. A lease that lets the landlord enter “for inspections, repairs, and emergencies” likely does not authorize entry for casual check-ins. The specificity cuts against reading in additional purposes.
The complication is implied terms. Courts sometimes read obligations into contracts that the parties did not spell out, such as duties of good faith, reasonable notice requirements, or industry customs, when doing so is necessary to make the agreement workable. Those implied terms can collide with expressio unius. If a contract explicitly lists three grounds for termination, does that exclude termination for fraud simply because fraud is not named? Most courts would say no. Some obligations are fundamental enough to survive even a detailed express list.
The line usually turns on whether the express terms look designed to be comprehensive. A carefully negotiated, exhaustive remedies clause sends a different signal than a short list of illustrative examples. The language around the list matters as much as the list itself.
Drafting Around the Canon
Because expressio unius turns specificity into a weapon, anyone drafting a statute or contract has to think about what a list leaves out, not just what it includes. The most common safeguard is the phrase “including but not limited to,” which signals that the items that follow are examples rather than a closed set.
Other drafting techniques serve the same goal:
- Adding an interpretation clause that defines “include,” “includes,” and “including” as non-limiting wherever they appear.
- Using catch-all provisions such as “and any other similar activities” or “or as otherwise determined by the board” to preserve flexibility.
- Writing broad categorical language (“any fraudulent act”) followed by examples for clarity, rather than a fixed list.
The tradeoff is real. Broad language prevents unintended exclusions but invites disputes about scope. A statute that reaches “any unfair business practice” will generate more litigation over its boundaries than one naming five specific prohibited acts. Skilled drafters combine categorical language with specific examples, making the scope clear without sealing it off.