n. 转向, 形成对立

Obversion \Ob*ver"sion\ ([o^]b*v[~e]r"sh[u^]n), n. [L. obversio
a turning towards.]
1. The act of turning toward or downward.

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.