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In logic and mathematics, necessity and sufficiency are terms used to describe a conditional or implicational relationship between two statements. For example, in the conditional statement : "If P then Q ", Q is necessary for P , because the truth of Q is guaranteed by the truth of P .
[2]: 649 For example, the utterance in (4) expresses that, according to what the speaker has observed, it is necessary to conclude that John has a rather high income: (4) John must be earning a lot of money. The modal base here is the knowledge of the speaker, the modal force is necessity.
For example, in deontic logic, (If it ought to be that p, then it is permitted that p) seems appropriate, but we should probably not include that . In fact, to do so is to commit the naturalistic fallacy (i.e. to state that what is natural is also good, by saying that if p is the case, p ought to be permitted).
A modal verb is a type of verb that contextually indicates a modality such as a likelihood, ability, permission, request, capacity, suggestion, order, obligation, necessity, possibility or advice. Modal verbs generally accompany the base (infinitive) form of another verb having semantic content. [ 1 ]
Because c) presumes b) will always be the case, it is a fallacy of necessity. John, of course, is always free to stop being a bachelor, simply by getting married; if he does so, b) is no longer true and thus not subject to the tautology a). In this case, c) has unwarranted necessity by assuming, incorrectly, that John cannot stop being a bachelor.
A sine qua non (/ ˌ s aɪ n i k w eɪ ˈ n ɒ n, ˌ s ɪ n i k w ɑː ˈ n oʊ n /, [1] Latin: [ˈsɪnɛ kʷaː ˈnoːn]) or conditio sine qua non (plural: conditiones sine quibus non) is an indispensable and essential action, condition, or ingredient.
^† This case is called lokál in Czech and Slovak, miejscownik in Polish, місцевий (miscevý) in Ukrainian and месны (miesny) in Belarusian; these names imply that this case also covers locative case. ^‡ The prepositional case in Scottish Gaelic is classically referred to as a dative case. Vocative case
Metaphysical necessity is contrasted with other types of necessity. For example, the philosophers of religion John Hick [2] and William L. Rowe [3] distinguished the following three: factual necessity (existential necessity): a factually necessary being is not causally dependent on any other being, while any other being is causally dependent on it.