Definify.com

Webster 1913 Edition

(ŏb-vẽr′shŭn)

Noun.

[L.

obversio

a turning towards.]

The act of turning toward or downward.

(Logic)

The act of immediate inference, by which we deny the opposite of anything which has been affirmed;

as, all men are mortal; then, by

obversion

, no men are immortal

. This is also described as “immediate inference by privative conception.”

Bain.

obversion ‎(countable and uncountable, plural obversions)

The act of turning toward or downward.
(logic) An immediate inference that denies the opposite of something previously affirmed.
All men are mortal, so, by obversion, no men are immortal.
- 1870, Alexander Bain, Logic: Induction
  From 'warmth is agreeable' we can affirm, by formal obversion, 'warmth is not disagreeable, and not indifferent.' We cannot affirm, without an examination of the subject matter, 'cold is disagreeable.'