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Sine qua non (/ /; Latin: [ˈsine kwaː ˈnoːn]) or condicio sine qua non (plural: condiciones sine quibus non) refers to an indispensable and essential action, condition, or ingredient. It was originally a Latin legal term for "[a condition] without which it could not be", or "but for..." or "without which [there is] nothing".
As a Latin term, it occurs in the work of Boethius, and originated in Aristotelian expressions. In recent times, it has passed from a merely legal usage to a more general usage in many languages, including English, German, French, Italian, Spanish, Catalan, etc. In Classical Latin, the form uses the word condicio (from the verb condico, condicere, to agree upon), but in later Latin the phrase is also used with conditio (condition). The phrase is also used in economics, philosophy and medicine.
An example of the term's usage was annotated in H. W. Brands' biography of Andrew Jackson. The book included a toast given by Jackson on the occasion of his receiving an honorary doctorate from Harvard University. The President responded to his listeners, "E pluribus unum, my friends. Sine qua non". A recent example comes from Javier Solana who said that the arrest of Radovan Karadžić was sine qua non for Serbia's joining the European Union and "it has been a very important step to move closer to Europe".
It appears in the expansive two volume text on Dahomey culture by Melville J. Herskovits. In writing about the need to learn the native language, he says, "This does not mean that a knowledge of a native language is a Sine qua non in the study of all problems bearing on primitive cultures. By the use of interpreters and of well recognized and tested techniques, it is possible to obtain the information needed to discover, describe and understand the institutions of a people, and it is such technique that have been employed in this study."
It also appears in the commentary on Article 59 of the Fourth Geneva Convention on the protection of civilians during a time of war. In this case, the sine qua non refers to the assurance that relief aid will go to the civilian population and not be diverted toward "the benefit of the Occupying Power".
In medicine, the term sine qua non is often used in regard to any sign, symptom, or finding whose absence would very likely mean absence of the target disease or condition. The test for such a sign, symptom or finding would thereby have very high sensitivity, and rarely miss the condition, so a negative result should be reassuring (the disease tested for is absent). Examples include:
In contrast, a pathognomonic sign or symptom is one whose presence would very likely mean presence of the target disease or condition. The tests for such signs are highly specific and very unlikely to give a false positive result.