The text also calls attention to multiple negations in one expression. A negation of a negation may yield affirmation, but only when the scope and level of the two negations are identified correctly.
Negating a negation is not identical to denying necessity. “It is not true that Zayd is absent” and “Zayd’s presence is not necessary” express different claims.
Therefore, merely counting the words “not” is insufficient. We must identify what each negation governs and at which logical level it operates.