obversion

American  

[ob-vur-zhuhn, -shuhn] / ɒbˈvɜr ʒən, -ʃən /

noun

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.”

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Etymology

Origin of obversion

1840–50; < Late Latin obversiōn- (stem of obversiō ) a turning toward, equivalent to obvers ( us ) ( obverse ) + -iōn- -ion

Example Sentences

This process is called Obversion, Permutation or Immediate Inference by Privative Conception; it is applicable to every proposition including O. A further process, known as Contraposition or Conversion by Negation, consists of conversion following on obversion.

From Project Gutenberg

Another term, Inversion, has been used by some logicians for a still more complicated process by the alternative use of conversion and obversion, which is applicable to A and E, and results in obtaining a proposition concerning the contradictory of the original subject; thus “all A is B” becomes “some not-A is not B.”

From Project Gutenberg

Hence the rule of Obversion;—Substitute for the predicate term its Contrapositive,5 and change the Quality of the proposition.

From Project Gutenberg

Dr. Bain includes also Material Obversion, the analogue of Formal Obversion applied to a Subject.

From Project Gutenberg

Dr. Bain calls this Material Obversion because it cannot be practised safely without reference to the matter of the proposition.

From Project Gutenberg