obversion

obversion

[ob-vur-zhuhn, -shuhn]
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.”

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

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World English Dictionary
obvert (ɒbˈvɜːt)
 
vb
1.  logic to deduce the obverse of (a proposition)
2.  rare to turn so as to show the main or other side
 
[C17: from Latin obvertere to turn towards; see obverse]
 
ob'version
 
n

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Encyclopedia Britannica
Encyclopedia

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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Encyclopedia Britannica, 2008. Encyclopedia Britannica Online.
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