[*] 214. Adverbs are regularly formed from Adjectives as follows: [*] a. From adjectives of the first and second declensions by changing the characteristic vowel of the stem to -ē: as, cārē, dearly, from cārus, dear (stem cāro-); amīcē, like a friend, from amīcus, friendly (stem amīco-).[*] b. From adjectives of the third declension by adding -ter to the stem. Stems in nt- (nom. -ns) lose the t-. All others are treated as i-stems:—
- fortiter, bravely, from fortis (stem forti-), brave.
- ācriter, eagerly, from ācer (stem ācri-), eager.
- vigilanter, watchfully, from vigilāns (stem vigilant-).
- prūdenter, prudently, from prūdēns (stem prūdent-).
- aliter, otherwise, from alius (old stem ali-).
[*] Note.--These adverbs are strictly cognate accusatives (§ 390).[*] e. The ablative singular neuter or (less commonly) feminine of adjectives, pronouns, and nouns may be used adverbially: as, falsō, falsely; citŏ , quickly (with shortened o ); rēctā ( viā ), straight (straightway); crēbrō, frequently; volgō, commonly; fortĕ, by chance; spontĕ, of one's own accord.
[*] Note.--Some adverbs are derived from adjectives not in use: as, abundē, plentifully (as if from †abundus; cf. abundō, abound); saepĕ, often (as if from †saepis, dense, close-packed; cf. saepēs, hedge, and saepiō, hedge in).