up:: Argumentation Theory
Argumentum a fortiori
Argumentum a fortiori (literally “argument from the stronger [reason]”) is a form of argumentation that draws upon existing confidence in a proposition to argue in favor of a second proposition that is held to be implicit in, and even more certain than, the first.
Usage
In ancient Indian logic (nyaya), the instrument of argumentation known as kaimutika or kaimutya nyaya is found to have resemblance with a fortiori argument. Kaimutika has been derived from the words kim uta meaning “what is to be said of”.
Examples
- If it is known that a person is dead on a certain date, it may be inferred a fortiori that he is exempted from the suspect list for a murder that took place on a later date, viz “Allen died on April 22nd, therefore, a fortiori, Allen did not murder Joe on April 23rd.”
- 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.