A proposition derived by negating and permuting the terms of another,equivalent proposition,for example,All not-Y is not-X is the contrapositive of All X is Y.

• 质位变换命题，由否定和置换另一等价命题的项而得到的命题；例如，“所有的非Y是非X”是“所有的X是Y”的质位变换命题。