Different operations can be performed on the same proposition.
Original: “All humans are animals.”
Contradictory: “Some humans are not animals” — opposed in truth value.
Simple converse: “Some animals are humans” — preserves the original’s truth.
Contradiction changes quantity and quality as needed to ensure opposite truth values. Conversion swaps subject and predicate while preserving truth and quality. These are not interchangeable operations.
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Simple Conversion: Definition, Categorical Rules and Reductio
Different operations can be performed on the same proposition.
Original: “All humans are animals.”
Contradictory: “Some humans are not animals” — opposed in truth value.
Simple converse: “Some animals are humans” — preserves the original’s truth.
Contradiction changes quantity and quality as needed to ensure opposite truth values. Conversion swaps subject and predicate while preserving truth and quality. These are not interchangeable operations.