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Rule of Contradiction

Contradictory statements are statements that differ in both quality and quantity

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Rule of Contraries

Two statements are contrary to one another if they are both universals but differ in quality

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Rule of Subcontraries

Two statements are subcontrary if they are both particular statements that differ in quality

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Rule of Subalterns

Two statements are subalternate if they have the same quality but differ in quantity

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1st Rule of Opposition

Contradictories cannot at the same time be true nor at the same time be false

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2nd Rule of Opposition

Contraries cannot at the same time both be true, but can at the same time both be false

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3rd Rule of Oppostion

Subcontraries may at the same time both be true, but cannot at the same time both be false

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4th Rule of Opposition

Subalterns may both be true or both be false

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Rule of Double Negation

A term which is not negated is equivalent to a term that is negated twice

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Essential Law of Argumentation

If the antecedent is true, the consequent must also be true

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Principle of Reciprocal Identity

Two terms that are identical with a third term are identical to each other

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Principle of Reciprocal Non-Identity

Two terms, one of which is identical with a third term and the other of which is nonidentical with that third term, are nonidentical to each other

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Dictum de Omni

What is affirmative universally of a certain term is affirmed of every term that comes under that term

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Dictum de Nullo

What is denied universally of a certain term is denied of every term that comes under that term

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Rule I

There must be three and only three terms

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Rule II

The middle term must not occur in the conclusion

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Rule III

If a term is distributed in the conclusion, then it must be distributed in the premises

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Rule IV

The middle term must be distributed at least once

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Rule V

No conclusion can follow from two negative premises

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Rule VI

If the two premises are affirmative, the conclusion must also be affirmative

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Rule VII

If either premise is negative, the conclusion must be negative

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Fallacy of Four Terms

There are four clearly distinguishable terms in a syllogism

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Fallacy of Equivocation

One of three terms is used in argument in two different senses

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Fallacy of Illicit Major

The major term is distributed in the conclusion but not in the major premise

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Fallacy of Illicit Minor

The minor term is distributed in the conclusion but not in the minor premise

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Fallacy of Undistributed Middle

The middle term is not distributed in either premise

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Fallacy of Exclusive Premises

When rule V is violated

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Fallacy of Drawing a Negative Conclusion from Affirmative Premises

when rule VI is violated

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Fallacy of Drawing an Affirmative Conclusion from Negative Premises

when rule VII is violated

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