Wikipedia:
a fortiori argument
The Latin phrase argumentum a fortiori literally means one of the following:
- "from the stronger"
- "even more so"
- "with even stronger reason"
It denotes a proof of a claim by means of an already proved stronger claim. Example: If it is forbidden to ride a bike with an extra passenger, then it is also forbidden to ride a bike with two extra passengers.
There are two types of the a fortiori argument:
- a maiore ad minus: from bigger to smaller
- a minore ad maius: from smaller to bigger
The a fortiori argument is most often used in order to reinforce a claim, though sometimes also to incorrectly justify a claim taking it as a premise (petitio principii).
References
- Grabenhorst, Thomas K.: Das argumentum a fortiori, Verlag „Peter Lang“ 1990 ISBN-Nummer 3-631-43261-5
- Schneider: Logik für Juristen, S. 158ff.
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