Conversion, Obversion, Contraposition
Obvert an E Proposition: No S is P
All S is nonP
Contrapose an A Proposition: All S is P
All nonP is nonS
Convert an A proposition: All S is P
By limitation: Some P is S
Contrapose an E Proposition: No S is P
By limitation: Some nonP is not nonS
Convert an E Proposition: No S is P
No P is S
Obvert an A Proposition: All S is P
No S is nonP
Contrapose an I Proposition: Some S is P
Not valid
Convert an O Proposition: Some S is not P
Not valid
Convert an I Proposition: Some S is P
Some P is S
Obvert an O Proposition: Some S is not P
Some S is nonP
Obvert an I Proposition: Some S is P
Some S is not nonP
Contrapose an O Proposition: Some S is not P
Some nonP is not nonS