Where does necessity collide?

In modal logic and metaphysics, necessity is the status of being true in every way things could have been: a necessarily true proposition, such as a truth of mathematics, could not have been false, and a necessary being is one that would exist in every possible situation. Plantinga's 1974 The Nature of Necessity developed this idea using possible worlds and drew the line between de dicto necessity, a whole statement's having to be true, and de re necessity, an object's having a property in every situation in which it exists. The referent is a logical or metaphysical status of propositions and things, what simply must be the case, and it is not a legal excuse for breaking a rule or a class of everyday goods.[1]

Unit

A proposition or being that holds in every possible situation

Recovery means

Not applicable

Measured by

Assessed by argument and modal reasoning, testing whether a claim could conceivably have been otherwise

In criminal law, the necessity defense is a justification that can excuse otherwise unlawful conduct when a person breaks the law to prevent a greater and imminent harm, choosing what the law treats as the lesser evil. Arnolds and Garland's 1975 review The Defense of Necessity in Criminal Law set out its requirements: an immediate threat, no reasonable lawful alternative, and harm avoided that outweighs the harm caused. The referent is a doctrine that weighs one court-recognised justification for conduct, so that an act normally punished is held blameless, and it is not a status that must hold in every possible world or a category of consumer goods.[2]

Unit

A recognised justification raised at trial to excuse one unlawful act

Recovery means

Not applicable

Measured by

Tested case by case against the doctrine's elements: imminence, no lawful alternative, and a favourable balance of harms

In consumer demand theory, a necessity good is one whose consumption grows more slowly than income, so that as people earn more they spend a smaller share of their budget on it: formally its income elasticity lies between zero and one, which sets it apart from a luxury, whose elasticity is above one. Deaton and Muellbauer's 1980 Economics and Consumer Behavior set this out within demand systems that estimate how spending on each good responds to income and prices. The referent is a category defined by a measured spending response, staples such as basic food, and it is not a status that must be true in every possible world or a courtroom justification for breaking the law.[3]

Unit

A good with an income elasticity of demand between zero and one

Recovery means

Not applicable

Measured by

Estimated from household budget data as the income elasticity of demand within a fitted demand system