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Syllogistic fallacies – logical fallacies that occur in syllogisms. Affirmative conclusion from a negative premise (illicit negative) – a categorical syllogism has a positive conclusion, but at least one negative premise. [11] Fallacy of exclusive premises – a categorical syllogism that is invalid because both of its premises are negative ...
The fallacy of four terms (Latin: quaternio terminorum) is the formal fallacy that occurs when a syllogism has four ... valid three term syllogism. [2] For example: ...
Each premise and the conclusion can be of type A, E, I or O, and the syllogism can be any of the four figures. A syllogism can be described briefly by giving the letters for the premises and conclusion followed by the number for the figure. For example, the syllogism BARBARA below is AAA-1, or "A-A-A in the first figure".
The fallacy of the undistributed middle occurs when the term that links the two premises is never distributed. In this example, distribution is marked in boldface: All Z is B; All Y is B; Therefore, all Y is Z; B is the common term between the two premises (the middle term) but is never distributed, so this syllogism is invalid.
Negative conclusion from affirmative premises is a syllogistic fallacy committed when a categorical syllogism has a negative conclusion yet both premises are affirmative. The inability of affirmative premises to reach a negative conclusion is usually cited as one of the basic rules of constructing a valid categorical syllogism.
Affirmative conclusion from a negative premise (illicit negative) is a formal fallacy that is committed when a categorical syllogism has a positive conclusion and one or two negative premises. For example: No fish are dogs, and no dogs can fly, therefore all fish can fly.
Another example is: If I am President of the United States, then I can veto Congress. I am not President. Therefore, I cannot veto Congress. [This is a case of the fallacy denying the antecedent as written because it matches the formal symbolic schema at beginning. The form is taken without regard to the content of the language.]
The fallacy of exclusive premises is a syllogistic fallacy committed in a categorical syllogism that is invalid because both of its premises are negative. [1] Example of an EOO-4 type invalid syllogism. E Proposition: No cats are dogs. O Proposition: Some dogs are not pets. O Proposition: Therefore, some pets are not cats. Explanation of Example 1: