Common Logical Fallacies
An inference is valid only when its premises guarantee its conclusion. A single assignment or interpretation with true premises and a false conclusion disproves validity.
Summary
An inference is valid only when its premises guarantee its conclusion. A single assignment or interpretation with true premises and a false conclusion disproves validity. In program verification, a plausible postcondition does not establish that the reasoning from preconditions is valid.
Three common invalid inference patterns are:
| Fallacy | Invalid pattern |
|---|---|
| Affirming the consequent | |
| Denying the antecedent |
🧠 Key Concepts
- Inference validity
- Counterexamples
- Affirming the consequent
- Denying the antecedent
- Inclusive disjunction
- Quantifier order
- Universal negation
- Circular reasoning
- Contraposition
- Valid inference rules
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A system accepts a valid password and then authenticates the user. A developer observes successful authentication and concludes that a password was used, although tokens can also authenticate users. Which best describes this reasoning?
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Common Logical Fallacies
📘 Overview A logical fallacy is an invalid inference: its premises can be true while its conclusion is false. In propositional logic, and represent propositions; in predicate logic, represents a statement about an element
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Part of 🌱 BSCS Year 1 — Computing & College Foundations
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