Interposition' Interposition is a term used in law and politics to describe the act of intervening between two parties or states. It is often used to refer to the action of a third party in a dispute, such as a mediator or arbitrator. In international law, interposition is the act of one state intervening in the affairs of another state, usually in an attempt to prevent or resolve a conflict. Interposition can also refer to the act of inserting something between two other things, such as a clause in a contract.