*obversion*

n. [ L. obversio a turning towards. ] 1. The act of turning toward or downward. [ 1913 Webster ]

2. (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. [ 1913 Webster ]