Regarding the etymology of modus ponens and modus tollens:
Modus is the Latin ancestor of English mode and mood. In logic, a mood is a way of constructing a valid syllogism. Ponens means affirming, from ponere, to affirm, to take a stand. Tollens means denying, from tollere, to deny. In the more leisurely past, modus ponens was known by the name modus ponendo ponens, indicating a mode of reasoning in which by affirming the antecedent (in the minor premise) we affirm the consequent (in the conclusion) Modus tollens was likewise known as modus tolllendo tollens, indicating a mode of reasoning in which by denying the consequent (in the minor premise) we deny the antecedent (in the conclusion).
Incidentally, these are the only valid modes of reasoning about hypothetical syllogisms, but hardly the only valid modes of syllogistic reasoning. Modus tollendo ponens is the valid mode of reasoning about alternative syllogisms:
p or q
not p
therefore q
That is, by denying either alternant (p or q) in the minor, we affirm the other alternant in the conclusion.
Obviously what's coming next is modus ponendo tollens, which is the valid mode of reasoning about disjunctive syllogisms:
not (p and q)
p
therefore not q
By affirming either disjunct (p or q) in the minor, we deny the other disjunct in the conclusion.
Finally, there are 19 valid categorical syllogisms (i.e. those involving propositions of the form all, none, some, and some not).
Ben Miller
Salem State College
[EMAIL PROTECTED]
Tim Gaines wrote:
I'm putting TIPS to the test this morning. In 30 minutes I'll
be talking to my Research Methods class about the logic of
testing theories, and one point I want to make is that neither
of the two logically valid modes of syllogistic reasoning
(modus ponens and modus tollens) permits confirmation of the
antecedent (the theory). It would be nice to be able to
provide the etiology of the terms, but I have loaned my copy
of Wason and Johnson-Laird to a student, and I can't seem to
find the terms in other references I have. Anyone know these
terms?Thanks,
Tim
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Tim Gaines [EMAIL PROTECTED]
Professor of Psychology phone: 864-833-8349
Presbyterian College fax: 864-833-8481
Clinton, SC 29325
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