N is Adj. When adjectives are used within a predicate, the adjectives conjugate much like verbs. Thus if we say that something is small, it's not so much the case that small is the adjective, but rather that the noun undergoes the action of being small, as if the 'is small' is a verb. Thus it is not so unusual that adjectives in this context conjugate.
Adjectives conjugate depending on tense and on whether they are used affirmatively or negatively. In the affirmative sense, the noun satisfies the adjective, but with the negative, the noun does not satisfy the negative. Adjectives change their form depending on the tense.