Syllogism
Syllogism
Syllogism
Names for the Valid Syllogisms premises (only one of which is universal) to derive a particular
affirmative conclusion:
A careful application of these rules to the 256 possible forms of
categorical syllogism (assuming the denial of existential import) The first in this group is AII-1 ("Darii"):
leaves only 15 that are valid. Medieval students of logic, relying on
syllogistic reasoning in their public disputations, found it convenient All M are P.
to assign a unique name to each valid syllogism. These names are Some S are M.
full of clever reminders of the appropriate standard form: their initial Therefore, Some S are P.
letters divide the valid cases into four major groups, the vowels in
order state the mood of the syllogism, and its figure is indicated by Converting the minor premise produces another valid form, AII-3
(complicated) use of m, r, and s. Although the modern interpretation ("Datisi"):
of categorical logic provides an easier method for determining the
validity of categorical syllogisms, it may be worthwhile to note the All M are P.
fifteen valid cases by name: Some M are S.
Therefore, Some S are P.
The most common and useful syllogistic form is "Barbara", whose
mood and figure is AAA-1:
The second pair begins with "Disamis" (IAI-3):
All M are P.
Some M are P.
All S are M.
All M are S.
Therefore, All S are P.
Therefore, Some S are P.
Instances of this form are especially powerful, since they are the
Converting the major premise in this case yields "Dimaris" (IAI-4):
only valid syllogisms whose conclusions are universal affirmative
propositions. Some P are M.
All M are S.
A syllogism of the form AOO-2 was called "Baroco": Therefore, Some S are P.
All P are M.
Some S are not M. Only one of the 64 distinct moods for syllogistic form is valid in all
Therefore, Some S are not P. four figures, since both of its premises permit legitimate
conversions:
The valid form OAO-3 ("Bocardo") is:
Begin with EIO-1 ("Ferio"):
Some M are not P.
No M are P.
All M are S.
Some S are M.
Therefore, Some S are not P.
Therefore, Some S are not P.