Talk:Disjunctive syllogism
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[edit] Self-contradictory redirections?
The second paragraph of Disjunctive syllogism's section Related argument forms claims that
Modus tollendo ponens should also not be confused with modus ponendo tollens.
but modus tollendo ponens and modus ponendo tollens both redirect to Disjunctive syllogism. Doesn't this contradict the above quoted passage?
192.102.214.6 16:58, 4 January 2007 (UTC)
I admit to not being proficient in logic or Latin, however I don't think it contradicts itself. What it is effectively saying is that by disputing a trait confirms the other, and that it can occur in two forms, one being the opposite of the other.
Eg. The cat is not black, therefore it is white. vs. The cat is not white, therefore it is black.
Both examples use the same form of logic, but prove the opposite logical conclusion.
It must be noted that this is my own personal judgement based on my own reasoning, therefore I may be overlooking missing information.
I suspect the last line was added by a different author to the first paragraph. I must also comment that there are no references to confirm the sources of the information. This would help to identify accurate information.
I do suggest providing an example in this section to help users understand it better.
--Minotaur500 17:49, 6 February 2007 (UTC)
Modus tollendo ponens should also not be confused with modus ponendo tollens They are not the same.
Modus tollendo ponens:
A v B ~A
B
modus ponendo tollens
~(A & B)
A
~B
it is just that in an exclusive or( A or B but not both)
((A v B) & ~(A & B)) They are both valid.
Hope this helps.
___________________________________________________________________________________________________ I am in a logic class. Both ponendo tollens and tollendo ponens are forms of disjunctive syllogisms, in fact they are also forms of conjunctive sylogisms. Anyway, the definitions are as follows...
Tollendo Ponens......Ponendo Tollens
Valid Syllogisms.........Invalid Syllogisms
1)............................1)
Either P or Q..............Either P or Q
Not P........................P
Therefore Q................Therefore not Q
2)............................2)
Either P or Q..............Either P or Q
Not Q........................Q
Therefore P................Therefore not P
Invalid Syllogisms.........Valid Syllogisms
3)............................3)
Not both P and Q.......Not both P and Q
Not P........................P
Therefore Q................Therefore not Q
4)............................4)
Not Both P and Q.......Not Both P and Q
Not Q........................Q
Therefore P................Therefore not P
There is no contradiction
[edit] Relevance logic
Shouldn't there be a section on how some logics, like relevance logic, deny DS in at least some cases? (Paraconsistent logics have to deny that DS applies in inconsistent situations on pain of having to admit the Principle of explosion, avoidance of which is usually one of the motivations for going paraconsistent in the first place).
