Sine qua non (/ˌsaɪni kweɪ ˈnɒn/; [ˈsine kwaː ˈnoːn]) or conditio sine qua non (plural: conditiones sine quibus non) is 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".
"Sine qua non" causation is the formal terminology for "but-for" causation.
Usage in language
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, 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".
Usage in medicine
In medicine, the term sine qua non (contrast with pathognomonic) 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:
"But-for" causation in law
In legal matters, "but-for", "sine qua non", causa sine qua non, or "cause-in-fact" causation, or conditio sine qua non, is a circumstance in which a certain act is a material cause of a certain injury or wrongdoing, without which the injury would not have occurred. It is established by the "but-for" test: but for the act having occurred, the injury would not have happened.
The defendant's negligent conduct is the actual cause of the plaintiff's injury if the harm would not have occurred to the plaintiff "but for" the negligent conduct of the defendant. (Perkins)
This type of causation is often contrasted with substantial-factor causation. The substantial factor test is used when there are multiple negligent tortfeasors which either (1) all caused the injury, in which case any and all of them are 100% joint and severally liable (treated as the group but suing the money) and the charged defendant would have to implead or sue the others to square the damages, or (2) only one could have actually caused the injury but they were all negligent in the same way and that one cannot be determined, in which case the burden shifts and any of them that cannot show their negligence was not the cause is 100% joint and severally liable. The purpose of this is allow the aggrieved party to get their damages, and make the negligent tortfeasors square up amongst themselves. See e.g. Hill v. Edmonds, (N.Y., 1966); Anderson v. Minneapolis, St. P. & S. St. M. Ry. Co., (Minn., 1920)
In Rogers v. Bromac Title Servs. LLC, the U.S. 5th Circuit interpreted the language of the Jury System Improvement Act in prohibiting employers from terminating employees "by reason of" jury service as meaning "but-for" causation: the employee must show that the termination of employment would not have occurred "but for" that jury service. This is a higher burden for the plaintiff employee than merely showing that the jury service was a motivating factor for the termination.