Tim-
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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