Modus Camestros

Form of a syllogism based on the Modus Celarent, in which a negative universal proposition is inferred from an affirmative and a negative existential proposition.

All P are M.

No S is M.

[and there exists at least one S]*

∴ Some S are not P.

For example:

All squares are rectangles.

No circle is a rectangle.

[and there exists at least one circle]*

∴ Some circles are not squares.

* Note: When an existential conclusion is inferred from universal premisses, this requires an (implicit or explicit) existential import, i.e. it must be proven that what the term refers to actually exists. In case of the Modus Camestros it is sufficient to prove existence for the minor term (S), as this also implies existence for M, while the conclusion does not actually require existence for P.

Modus Camestros is similar to Modus Camestres, but is the weaker of the two forms, as it infers a existential statement rather than an universal one.

The name “Camestros” is a mnemonic term that helps to remember the most important characteristics of this mode: The “C” at the beginning indicates that it is related to the Modus Celarent, the “a” and “e” mark the affirmative and negative universal statements in the premisses, the “o” a negative existential conclusion.

• Modus Camestrop

• Existential fallacy
• Existential import
• Existential quantification
• Modus Celarent
• Syllogism
• Universal Quantification