Existential fallacy

Existential fallacy

The existential fallacy, or existential instantiation, is a logical fallacy committed in a categorical syllogism that is invalid because it has two universal premises and a particular conclusion. In other words, for the conclusion to be true, at least one member of the class must exist, but the premises do not establish this.

Examples

*All inhabitants of other planets are friendly, and all Martians are inhabitants of another planet. Therefore, there are friendly Martians. (The conclusion assumes there really are Martians in existence.)
*All unicorns are animals, therefore some animals are unicorns. (This conclusion assumes that unicorns exist.)

The existential fallacy is a syllogistic fallacy. Modern logical constructs, however, allow for conditional logic ("If unicorns existed...")

Also in the form of a Syllogism

ee also

*Vacuous truth

External links

* [http://www.fallacyfiles.org/existent.html Fallacy files: existential fallacy]
* [http://www.swif.uniba.it/lei/foldop/foldoc.cgi?existential+fallacy FOLDOC: existential fallacy]


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