[*] 174. The parent (Indo-European) speech from which Latin comes had two main classes of verbs:—
- Thematic Verbs, in which a so-called thematic vowel (e/o, in Latin i/u) appeared between the root and the personal ending: as, leg-i-tis (for †leg-e-tes ), leg-u-nt (for †leg-o-nti ).1
- Athematic Verbs, in which the personal endings were added directly to the root: as, es-t , es-tis (root ES)2, dă-mus (dō, root DA), fer-t ( ferō , root FER).
- Verbs which preserve the thematic vowel eor o (in Latin i or u) before the personal endings.—These make up the Third Conjugation. The present stem is formed in various ways (§ 176), but always ends in a short vowel e/o (Latin i/u ). Examples are tegō (stem ( tege/o- ), sternimus (stem ( sterne/o- ) for †ster-no-mos, plectunt (stem ( plecte/o- ) for †plec-to-nti. So nōscō (stem ( gnōsce/o- ) for gnō-sc-ō. Verbs like nōscō became the type for a large number of verbs in -scō, called inceptives (§ 263. 1).
- Verbs which form the present stem by means of the suffixye/o-, which already contained the thematic vowele/o.—Verbs of this class in which any vowel (except u ) came in contact with the suffix ye/o-suffered contraction so as to present a long vowel ā-, ē-, ī-, at the end of the stem. In this contraction the thematic e/o disappeared. These became the types of the First, Second, and Fourth conjugations respectively. In imitation of these long vowel-stems numerous verbs were formed by the Romans themselves (after the mode of formation had been entirely forgotten) from noun- and adjective-stems. This came to be the regular way of forming new verbs, just as in English the borrowed suffix -ize can be added to nouns and adjectives to make verbs: as, macadamize, modernize.