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Modus Barbara

Syllogism in which a new general statement is inferred from two universal quantifications.

All M are P.
All S are M.

All S are P.

For example:

All rectangles are polygons.
All squares are rectangles.

All squares are polygons.

Name

The word “Barbara” is not a name in this context, but rather a mnemonic term in which the vowels (a-a-a) indicate that all three statements, i.e. the two premises as well as the conclusion, are all affirmative universal quantifications (type “a”).

For more information on the naming and on syllogisms in general, see the page on syllogisms in the glossary.

Sorites

Instead of the usual two premises, there is in principle no limit to the number of conditional statements that can be chained to reach a conclusion. Such a sequence of conditionals “stacked” together is also called a “Sorites”, from the Greek word for “heap”.

Conversely, the Modus Barbara could also be considered a special case of the sorites with exactly three terms in two premises.

Variants

All of the following variants can be transformed into a valid Modus Barbara. However, the first two (Baroco and Bocardo) require further proof of validity for this transformation:

See also

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About this site

Ad Hominem Info is a project to explain and categorize the most common systematic fallacies and fallacies. On this page, you will find a background article that briefly explains an important logical concept, which may be needed to better understand another article in this area.
For more information, please see the main category “logic

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