obversion

In the obversion of the original proposition to an 'E' type proposition, both terms become distributed.

Obversion changes the quality (that is the affirmativity or negativity) of the statement and the predicate term.

The successive applications of conversion and obversion within the process of contraposition may be given by a variety of names.

Because of this, obversion can be used to determine the immediate inferences of all categorical propositions, regardless of quality or quantity.

Contraposition also has distinctive applications in its philosophical application distinct from the other traditional inference processes of conversion and obversion where equivocation varies with different proposition types.

However, although the resulting propositions from obversion are logically equivalent to the original statements in terms of truth-value, they are not semantically equivalent to their original statements in their standard form.

In the obversion of a particular negative to a particular affirmative the quantity of the subject also remains unchanged, and the predicate term is changed from simple negation to a term of the complementary class.

In addition, obversion allows us to navigate through the traditional square of logical opposition by providing a means for us to proceed from "A" Propositions to "E" Propositions, as well as from "I" Propositions to "O" Propositions, and vice versa.

However it can be rewritten as a standard form AAA-1 syllogism by first substituting the synonymous term "humans" for "people" and then by reducing the complementary term "immortal" in the first premise using the immediate inference known as obversion (that is, "No humans are immortal."