The maxim expressio unis est exclusio alterius

The maxim expressio unis est exclusio alterius ("to express one thing is to exclude another") allows the courts to imply that where an Act applies a rule to a particular situation, the Oireachtas intended to confine the rule to that situation, and not to apply it in any wider context.

The maxim was applied in Kiely v Minister for Social Welfare and again in O'Connell v An t-Ard Chlaraitheoir . It was succinctly illustrated by Henchy J in Keily when he said:

"The fact that article 11 (5) allows a written statement to be received in evidence in the specified limited circumstances means that it cannot be received in other circumstances: expressio unius est exclusio alterius ".

The maxim has limitations, however, and will not apply where a legislative provision merely states a particular aspect or a particular application of a more general rule of law. This was accepted by the Irish courts in The State (Minister for Lands and Fisheries) v Judge Sealy and in Inspector of Taxes v Arida Ltd .