Simple conversion preserves the quality of the proposition.
Original: Some flowers are fragrant.
Converse: Some fragrant things are flowers.
Not its converse: Some fragrant things are not flowers.
The last changes an affirmative into a negative; it may be separately true, but it does not follow by simple conversion.
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Quality must be preserved
Simple Conversion of Propositions: Definition, Method and Rules
Simple conversion preserves the quality of the proposition.
Original: Some flowers are fragrant.
Converse: Some fragrant things are flowers.
Not its converse: Some fragrant things are not flowers.
The last changes an affirmative into a negative; it may be separately true, but it does not follow by simple conversion.