Existential fallacy
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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 a member of the class must exist, but the premises do not establish this.
Example:
- All inhabitants of another planet are friendly people, and all Martians are inhabitants of another planet. Therefore, some Martians are friendly people. (The conclusion assumes there really are some Martians in existence.)
The existential fallacy is a syllogistic fallacy.
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| Argument from fallacy | Fallacy of modal logic | Masked man fallacy | Appeal to probability
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| Fallacy of propositional logic: | |
| Affirming a disjunct | Affirming the consequent | Commutation of Conditionals Denying a conjunct | Denying the antecedent | Improper Transition |
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| Fallacy of quantificational logic: | |
| Existential fallacy | Illicit Conversion | Quantifier shift | Unwarranted contrast | |
| Syllogistic fallacy: | |
| Affirmative conclusion from a negative premise | Negative conclusion from an affirmative premise Exclusive premisses | Necessity | Four-term Fallacy | Illicit major | Illicit minor | Undistributed middle |
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| Other types of fallacy | |
This article was originally based on material from the Free On-line Dictionary of Computing, which is licensed under the GFDL.
