Necessary

Necessary is a term used in various fields such as philosophy, logic, mathematics, and law to denote something that is needed, required, or cannot be done without. The concept of necessity is often contrasted with that of contingency, which refers to things that could be otherwise.

Philosophy

In philosophy, a necessary truth is one that could not have been otherwise. It is the opposite of a contingent truth, which could have been otherwise. For example, the statement "all bachelors are unmarried" is a necessary truth because it is impossible for a bachelor to be married.

Logic

In logic, a necessary condition is one that must be satisfied for a statement to be true. For example, in the statement "if it is raining, then the ground is wet," the rain is a necessary condition for the ground being wet. This is contrasted with a sufficient condition, which is enough to guarantee the truth of a statement, but not required.

Mathematics

In mathematics, a necessary condition is one that must be met for a theorem or equation to hold true. For example, for a number to be even, it is necessary that it be divisible by 2. This is contrasted with a sufficient condition, which, if met, guarantees the truth of the theorem or equation, but is not required.

Law

In law, necessity is a defense used in criminal cases to justify actions that would otherwise be illegal. The defense of necessity is based on the principle that the law should not punish those who, in a crisis, choose the lesser of two evils. For example, if a person breaks into a house to escape a raging fire, they may be able to use the defense of necessity to avoid a charge of burglary.

See also

• Necessity and sufficiency
• Necessity (criminal law)
• Necessity in international law
• Principle of sufficient reason
• Modal logic