obversion, conversion and contraposition

conversion

interchange the subject and predicate terms in a categorical proposition

All P are S invalid

conversion of A and validity

No P are S valid

conversion of E and validity

Some P are S valid

conversion of I and validity

Some P are not S invalid

conversion of O and validty

valid for E and I statements

validity of conversions

complement

class containing things that are not members of a given class

term-complement

word or phrases that denote the complement class i..e. 'non-trees'

obversion

change quality from affirmative t negative (or vice versa), and replace predicate terms with their term-complement

No S are non-P

obversion of A

All S are non-P

obversion of E

Some S are not non-P

obversion of I

Some S are non-P

obversion of O

valid in every categorical form

validity of obversion

contraposition

replace subject and predicate terms with their term complements and switch them around

All non-P are non-S

contrapositive of A

No non-P are non-S

contrapositive of E

Some non-P are non-S

contrapositive of I

Some non-P are not non-S

contrapositive of O

valid inferences for A and O forms

validity of contrapositive