Argumentum a fortiori
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Argumentum a fortiori (UK: /
- If a person is dead (the stronger reason), then one can with equal or greater certainty argue a fortiori that the person is not breathing. "Being dead" trumps other arguments that might be made to show that the person is dead, such as "he is no longer breathing"; therefore, "he is no longer breathing" is an extrapolation from his being dead and is a derivation of this strong argument.
- If driving 10 mph over the speed limit is punishable by a fine of $50, it can be inferred a fortiori that driving 20 mph over the speed limit is also punishable by a fine of at least $50.
- If a teacher refuses to add 5 points to a student's grade, on the grounds that the student does not deserve an additional 5 points, it can be inferred a fortiori that the teacher will also refuse to raise the student's grade by 10 points.
In Garner's Modern American Usage , Bryan A. Garner explained writers sometimes use a fortiori as an adjective as in "a usage to be resisted." Garner provides this example:"Clearly, if laws depend so heavily on public acquiescence, the case of conventions is an a fortiori [read even more compelling] one."
A fortiori arguments are regularly used in Jewish law under the name kal va-chomer, literally "mild and severe", the mild case being the one we know about, while trying to infer about the more severe case.
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A maiore ad minus
In logic, a maiore ad minus describes a simple and obvious inference from a claim about a stronger entity, greater quantity, or general class to one about a weaker entity, smaller quantity, or specific member of that class:
- From general to particular ("What holds for all X also holds for one particular X")
- From greater to smaller ("If a door is big enough for a person two metres high, then a shorter person may also come through"; "If a canister may store ten litres of petrol, then it may also store three litres of petrol.")
- From the whole to the part ("If the law permits a testator to revoke the entirety of a bequest by destroying or altering the document expressing it, then the law also permits a testator to revoke the portion of a bequest contained in a given portion of a document by destroying or altering that portion of the document.")
- From stronger to weaker ("If one may safely use a rope to tow a truck [in the American usage], one may also use it to tow a car.")
A minore ad maius
The reverse, less known and less frequently applicable argument is a minore ad maius, which denotes an inference from smaller to bigger.
“Argumentum a maiori ad minus” (from the greater to the smaller) – works in two ways:
- “who may more, all the more so may less” and relates to the statutory provisions that permit to do something
- “who is ordered more, all the more so, is ordered less” and relates to the stautory provisions that order to do something
“Argumentum a minori ad maius” (from the smaller to the greater) – works in the way:
- Morwood, James (1998). A Dictionary of Latin Words and Phrases. Oxford: Oxford University Press. pp. x–xii. ISBN 978-0-19-860109-8.
- Garner, Bryan A. (2009). Garner's Modern American Usage (3rd ed.). Oxford: Oxford University Press. p. 28. ISBN 978-0-19-538275-4.
- Abramowitz, Jack. "Torah Methodology #1 – Kal v'Chomer". Orthodox Union. Retrieved 20 July 2016.
- Hallaq, Wael (2009). Sharī'a: Theory, Practice, Transformations (1st ed.). Cambridge: Cambridge University Press. p. 105. ISBN 0521678749.