Contradiction is an opposition in which one proposition's truth requires the other's falsehood and conversely. Relevant identities must hold so the negation targets precisely the same judgment.
Singular proposition: exact denial about the same individual and predicate.
Quantified proposition: appropriate change of quantity and quality.
Modal proposition: correct treatment of the scope of necessity, permanence and possibility.
Conditional proposition: agreement of genus and species with negation of the whole conditional judgment.
The next chapter is al-ʿaks al-mustawī (simple conversion). Instead of negating a proposition, it reverses the relevant terms and asks when truth is preserved.