Proving too much

{{One source|date=October 2021}}

{{Short description|Logical fallacy}}In philosophy, proving too much is a logical fallacy which occurs when an argument reaches the desired conclusion in such a way as to make that conclusion only a special case or corollary consequence of a larger, obviously absurd conclusion. It is a fallacy because, if the reasoning were valid, it would hold for the absurd conclusion.

The judgement of fallacy is therefore largely dependent on a normative judgement of the "absurd" conclusion. A charge of "proving too much" is thus generally invoked, rightly or wrongly, against normatively-opposed conclusions, and so such charges are often controversial at the time they are made, as in the following examples: {{Cite book |last=Arp |first=Robert |title=Bad arguments: 100 of the most important fallacies in western philosophy |last2=Barbone |first2=Steven |last3=Bruce |first3=Michael |date=2019 |publisher=Wiley Blackwell |isbn=978-1-119-16578-1 |location=Hoboken (N.J.)}}

• Gaunilo argued that Anselm's ontological argument, that God exists because he is the greatest conceivable being and to exist is greater than to not exist, proves too much, because Gaunilo believed a parallel argument could be made proving the existence of a perfect island.{{cite journal|last1=Mizrahi|first1=Moti|title=On Proving Too Much|journal=Acta Analytica}}

• The Georgia-born American educator Henry Coppée in 1850 described in his "Elements of Rhetoric" that if one argues that slavery is evil because masters are put into situations where they can beat slaves to death, then marriage and parenthood are also evil because domestic violence exists.{{cite book|last=Coppée|first=Henry|authorlink=Henry Coppée|title=Elements of rhetoric: designed as a manual of instruction|url=https://archive.org/stream/elementsrhetori01coppgoog#page/n240/mode/1up/search/proving|year=1850|publisher=J.H. Butler & Co.|page=234}}

Showing that an opponent has proved too much is a form of reductio ad absurdum.