[ob-vur-zhuh
n, -shuhn] 
| 1. | an act or instance of obverting. |
| 2. | something that is obverted. |
| 3. | Logic. a form of inference in which a negative proposition is obtained from an affirmative, or vice versa, as “None of us is immortal” is obtained by obversion from “All of us are mortal.” |
| ob·ver·sion (ŏb-vûr'zhən, -shən, əb-) n.
|
obversion
in syllogistic, or traditional, logic, transformation of a categorical proposition (q.v.), or statement, into a new proposition in which (1) the subject term is unchanged, (2) the predicate is replaced by its contradictory, and (3) the quality of the proposition is changed from affirmative to negative or vice versa. Thus the obverse of "Every man is mortal" is "No man is immortal." Because the obverse of any categorical proposition is logically equivalent to it, obversion is a form of immediate inference. See also conversion
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