of necessity

ne·ces·si·ty   (nə-sěs'ĭ-tē)    n.   pl. ne·ces·si·ties The condition or quality of being necessary. Something necessary: The necessities of life include food, clothing, and shelter. Something dictated by invariable physical laws. The force exerted by circumstance. Something dictated by invariable physical laws. The force exerted by circumstance. The state or fact of being in need. Pressing or urgent need, especially that arising from poverty. [Middle English necessite, from Old French, from Latin necessitās, from necesse, necessary; see necessary.]

Main Entry: ne·ces·si·ty
Function: noun
Inflected Form: plural -ties
1 a : the presence or pressure of circumstances that justify or compel a certain course of action; especially : a need to respond or react to a dangerous situation by committing a criminal act b : an affirmative defense originating in common law that the defendant had to commit a criminal act because of the pressure of a situation that threatened a harm greater than that resulting from the act —see also choice of evils defense at DEFENSE 2a —compare DURESS, UNDUE INFLUENCE
2 : something that is necessary esp. to subsistence necessities of food, clothing, and shelter>

of necessity

Also, out of necessity. As an inevitable consequence, unavoidably, as in the New Testament: "Of necessity he must release one unto them at the Feast" (Luke 23:17). [Late 1300s]