“Every human is an animal” and “Every nonanimal is nonhuman” can both be true. They are therefore not contradictories.
In contradiction, the truth of a proposition requires the falsity of its contradictory. In contraposition, a true premise supports a true transformed proposition.
The word “negation” in the name refers to complementary terms, not to constructing the logical contradictory of the whole proposition.
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Contraposition: Classical Rules, Validity and the Later Convention
“Every human is an animal” and “Every nonanimal is nonhuman” can both be true. They are therefore not contradictories.
In contradiction, the truth of a proposition requires the falsity of its contradictory. In contraposition, a true premise supports a true transformed proposition.
The word “negation” in the name refers to complementary terms, not to constructing the logical contradictory of the whole proposition.