Check a proposed contrapositive with four questions:
1. Have the complete subject and predicate concepts been identified?
2. Are their complements formed correctly?
3. Has one convention—earlier or later—been used consistently?
4. Must the new proposition be true whenever the original is true?
A true premise with a false proposed result is enough to expose an invalid general rule. This tests logical validity, not merely memorized names.
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Contraposition: Classical Rules, Validity and the Later Convention
Check a proposed contrapositive with four questions:
1. Have the complete subject and predicate concepts been identified?
2. Are their complements formed correctly?
3. Has one convention—earlier or later—been used consistently?
4. Must the new proposition be true whenever the original is true?
A true premise with a false proposed result is enough to expose an invalid general rule. This tests logical validity, not merely memorized names.