Proportionality is a general principle in law which covers several separate concepts:The concept of proportionality is used as a criterion of fairness and justice in statutory interpretation processes, especially in constitutional law, as a logical method intended to assist in discerning the correct balance between the restriction imposed by a corrective measure and the severity of the nature of the prohibited act. Within criminal law, the concept is used to convey the idea that the punishment of an offender should fit the crime. Under international humanitarian law governing the legal use of force in an armed conflict, distinction, proportionality, and necessity are important factors in assessing military necessity. Under the United Kingdom's Civil Procedure Rules, costs must be "proportionately and reasonably incurred", or "proportionate and reasonable in amount", if they are to form part of a court ruling on costs.