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Dr. Jay
VerLinden
Communication
Department
College of Arts, Humanities
and Social Sciences
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Argumentation and Critical Thinking Tutorial

FORMAL VALIDITY REVIEW

This page reviews the logical requirements for a syllogism to be formally valid. It does not contain explanations for any of the concepts, so you should be sure to read some material on formal validity before you take the tests.

VALIDITY REQUIREMENT FOR THE CATEGORICAL SYLLOGISM

  1. The argument must have exactly three terms.
  2. Every term must be used exactly twice.
  3. A term may be used only once in any premise.
  4. The middle term of a syllogism must be used in an unqualified or universal sense. The middle term of an enthymeme may be used in a qualified or non-universal sense.
  5. A term may be distributed in the conclusion only if it has been distributed in the major or minor premise.
  6. At least one of the premises must be stated in the affirmative.
  7. If one premise is negative, the conclusion must be negative.

VALIDITY REQUIREMENT FOR THE DISJUNCTIVE SYLLOGISM

  1. The minor premise must accept one alternative in the major premise, or reject all but one alternative.
  2. If the minor premise accepts one alternative, the conclusion must reject all other alternatives.
  3. If the minor premise rejects all but one alternative, the conclusion must accept the remaining alternative.

VALIDITY REQUIREMENTS FOR THE CONDITIONAL OR HYPOTHETICAL SYLLOGISM

  1. The minor premise must either affirm the antecedent or deny the consequent.
  2. If the minor premise affirms the antecedent the conclusion must affirm the consequent.
  3. If the minor premise denies the consequent the conclusion must deny the antecedent.

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