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 **

- The argument must have exactly three terms.
- Every term must be used exactly twice.
- A term may be used only once in any premise.
- 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.
- A term may be distributed in the conclusion only if it has
been distributed in the major or minor premise.
- At least one of the premises must be stated in the affirmative.
- If one premise is negative, the conclusion must be negative.

**VALIDITY REQUIREMENT FOR THE DISJUNCTIVE
SYLLOGISM **

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

**VALIDITY REQUIREMENTS FOR THE CONDITIONAL
OR HYPOTHETICAL SYLLOGISM **

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

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