Expressio unius est exclusio alterius

Expressio unius est exclusio alterius means that the express mention of one thing implies the exclusion of another. As an aid to interpretation of statutes and documents, it suggests that where the legislature or the parties have specifically listed certain persons, things or modes, they intended to leave out those not listed. A related form is expressum facit cessare tacitum: what is expressed makes what is implied silent.

The maxim is an aid, not a rule of law, and courts apply it with caution. It yields where the context shows that the list was illustrative rather than exhaustive, where the omission was accidental, or where applying it would produce an absurd or unjust result or defeat the purpose of the provision. It is commonly used when a statute prescribes a particular manner of doing a thing; the inference is that it must be done in that manner and not otherwise. It differs from ejusdem generis, which restricts general words following specific words to things of the same class, and from noscitur a sociis, which reads a word in the light of its companions. Expressio unius operates on what is omitted; those maxims operate on what is included.

The maxim also guides the reading of contracts. In A.B.C. Laminart Pvt. Ltd. v. A.P. Agencies, Salem (1989), the Supreme Court considered a clause making disputes 'subject to Kaira jurisdiction'. It held that words such as 'alone', 'only' or 'exclusive' make the exclusion of other competent courts clear, and that without them the maxim expressio unius est exclusio alterius may apply in an appropriate case. On the facts, the clause did not clearly exclude the Salem court, which therefore had jurisdiction.

Examiners usually ask for the meaning of the maxim, its contrast with ejusdem generis and noscitur a sociis, and its use in construing jurisdiction clauses.