Find accurate definitions of over 5,000 Catholic terms and phrases (including abbreviations). Based on Fr. John Hardon's Modern Catholic Dictionary, © Eternal Life. Used with permission.
Whatever must be or cannot not be and should be. Various kinds of necessity are the basis for all others. Something may be necessary because it cannot not exist; its essence is to exist. It is in this sense that God is necessary Being. This is a necessity of being. Or something may be necessary in order to verify something else, as a rational soul is necessary to human nature, or four equal sides are necessary to have a square. This is a necessity of essence. Or something may be necessary in order to attain a given purpose or achieve a given end, as it is necessary to eat in order to live. This is a necessity of means. Or something may be necessary because God wills it so and wants humanity to do it, as it is necessary to pray in order to be saved. This is a necessity of obligation or moral necessity. (Etym. Latin necessitas, ne-, not + cedere, to withdraw: that which cannot be other than it is, with respect to itself or with respect to another thing.)