View source for Modus non excipiens

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In [[logic]], '''modus non excipiens'''<ref>Bart Verheij, ’Logic, Context and Valid Inference
Or: Can There be a Logic of Law’, 2000. Available
on bart.verheij@metajur.unimaas.nl,
[http://www.metajur.unimaas.nl/˜bart/]</ref><ref>Walton, Douglas; ''Are Some Modus Ponens Arguments Deductively Invalid?'', University of Winnipeg</ref>  is a [[Validity (logic)|valid]] [[rule of inference]] that is closely related to [[modus ponens]]. This [[argument form]] was created by Bart Verheij to address certain arguments which are types of ''modus ponens'' arguments, but must be considered to be invalid. An instance of a particular ''modus ponens'' type argument is

:A large majority accept A as true. Therefore, there exists a presumption in favor of A.

However, this is an ''[[argumentum ad populum]]'', and is not deductively valid. The problem can be addressed by drawing a distinction between two types of inference identified by Verheij:

''Modus ponens'':
:Premises:
:*As a rule, if P then Q
:*P
:Conclusion:
:*Q

and

''Modus non excipiens''
:Premises:
:*As a rule, if P then Q
:*P
:*It is not the case that there is an exception to the rule that if P then Q
:Conclusion:
:*Q

==References==
{{reflist}}

[[Category:Rules of inference]]
[[Category:Theorems in propositional logic]]