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, at least one member of the class must exist, but the premises do not establish this.

Contents 1 Example 2 See also 3 References 4 External links

[edit] Example

1- All inhabitants of other planets are friendly
2- All Martians are inhabitants of another planet.

3- Some Martians are friendly.

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

The fallacy does not occur in enthymemes, where hidden premises required to make the syllogism valid assume the existence of at least one member of the class.

[edit] See also

• Vacuous truth

[edit] References

[edit] External links

• Fallacy files: existential fallacy
• FOLDOC: existential fallacy

v • d • e Formal fallacies Masked man fallacy • Appeal to probability • Bare assertion fallacy Fallacy of propositional logic: Affirming a disjunct • Affirming the consequent • Argument from fallacy • False dilemma • Denying the antecedent Fallacy of quantificational logic: Existential fallacy • Illicit Conversion • Proof by example • Quantifier shift Syllogistic fallacy: Affirmative conclusion from a negative premise • Exclusive premises • Necessity • Four-term Fallacy • Illicit major • Illicit minor • Undistributed middle List of fallacies (formal and informal) • Other types of formal fallacy

This article was originally based on material from the Free On-line Dictionary of Computing, which is licensed under the GFDL.

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