An immediate inference is an inference which can be made from only one statement
or proposition. The result of this inference is a logically equivalent statement form to
the given statement.
Converse
Conversion is the inference in which the subject and predicate are interchanged. The
valid converse is logically equivalent to the original proposition.
Examples:
Convertend
SaP All men are mortals.
SiP Some politicians are liars.
SeP No stones are flowers.
SoP Some animals are not mammals.
Converse
PiS Some mortals are men.
PiS Some liars are politicians.
PeS No flowers are stones.
--no converse
Obverse
Obversion is the inference in which the quality of the proposition is changed and the
predicate is interchanged with its complement. It is valid for all four forms.
Examples:
Obvertend
SaP All men are mortals.
SiP Some politicians are liars.
SeP No stones are flowers.
SoP Some animals are not mammals.
Obverse
Se˥P No men are non-mortals.
So˥P Some politicians are not non-liars.
Sa˥P All stones are non-flowers.
Si˥P Some animals are non-mammals.
Contrapositive
Contraposition is the inference in which the subject is interchanged with the
complement of the predicate and the predicate is interchanged with the complement
of the subject.
Examples:
Contraposend
SaP All men are mortals.
SiP Some politicians are liars.
SeP No stones are flowers.
SoP Some animals are not mammals.
Contraposit
˥PeS No non-men are mortals.
--no contraposit
˥PiS Some non-flowers are stones.
˥PiS Some non-mammals are animals.