2. Adjectives in -us, preceded by a vowel; as, idōneus, adapted; arduus, steep; necessārius, necessary.
a. Adjectives in -quus, of course, do not come under this rule. The first u in such cases is not a vowel, but a consonant.
Adjectives not admitting Comparison.
[75]. Here belong—
1. Many adjectives, which, from the nature of their signification, do not admit of comparison; as, hodiernus, of to-day; annuus, annual; mortālis, mortal.
2. Some special words; as, mīrus, gnārus, merus; and a few others.
FORMATION AND COMPARISON OF ADVERBS.
[76]. Adverbs are for the most part derived from adjectives, and depend upon them for their comparison.
1. Adverbs derived from adjectives of the First and Second Declensions form the Positive by changing -ī of the Genitive Singular to -ē; those derived from adjectives of the Third Declension, by changing -is of the Genitive Singular to -iter; as,—