Obversion /(ŏb*vẽr"shŭn)/

Ob·ver·sion

Obversion

n.
  1. The act of turning toward or downward.
  2. 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.” (Logic)