obversion

Noun

1. The act of turning toward or downward.
2. An immediate inference that denies the opposite of something previously affirmed.
   • All men are mortal, so, by obversion, no men are immortal.
   • 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.' - 1870, Alexander...