Complement of a term versus denial of a proposition

Contraposition: Classical Rules, Validity and the Later Convention

The complement of the concept “human” is nonhuman; the complement of “animal” is nonanimal. These are terms, not complete propositions.

“Zayd is not human” is a negative proposition; “nonhuman” is a concept applicable to whatever is not human.

Contraposition works with complementary terms. The presence of “non-” within a term must not be confused with the denial of an entire proposition.