%contraries%

n. pl. [ Pl. of Contrary, n. ] (Logic) Propositions which directly and destructively contradict each other, but of which the falsehood of one does not establish the truth of the other. [ 1913 Webster ]

If two universals differ in quality, they are contraries; as, every vine is a tree; no vine is a tree. These can never be both true together; but they may be both false. I. Watts. [ 1913 Webster ]