a. In the First, Second, and Fourth conjugations, by adding a long vowel (á-, é-, í-) to the root, whose vowel is sometimes changed: as, vocá-re (VOC), moné-re (MEN, cf. meminí), sopí-re (SOP).[Most verbs of the First, Second, and Fourth Conjugations form the present stem by adding the suffix -yeo to a noun-stem. The á of the First Conjugation is the stem-ending of the noun (as, plantá-re, from plantá-, stem of planta). The é of the Second and the í of the Fourth Conjugation are due to contraction of the short vowel of the noun-stem with the ending -yeo-. Thus albére is from albeo-, stem of albus; fíníre is from fíni-, stem of fínis. Some verbs of these classes, however, come from roots ending in a vowel.]
NOTE: Verb-stems of these conjugations are almost all really formed from noun-stems on the pattern of older formations (see § 174).
b. In the Third Conjugation, by adding a short vowel eo[This is the so-called ``thematic vowel.''] to the root. In Latin this eo usually appears as iu, but e, is preserved in some forms. Thus, tegi-s (root TEG), ali-tis (AL), regu-nt (REG); but tege-ris (tege-re), ale-ris.
d. In some verbs the present stem is formed from a noun-stem in u-: as, statu-e-re (statu-s), aestu-á-re (aestu-s); cf. acuó, acuere.[These are either old formations in -yeo- in which the y has disappeared after the u (as, statuó for statu-yó) or later imitations of such forms.]
NOTE 1: A few isolated forms use the simple root as a present stem: as, fer-re, fer-t; es-se; vel-le, vul-t. These are counted as irregular.
NOTE 2: In some verbs the final consonant of the root is doubled before the stem-vowel: as, pell-i-tis (PEL), mitt-i-tis (MIT).
e. Some verbs have roots ending in a vowel. In these the present stem is generally identical with the root: as, da-mus (DA), flé-mus (stem flé-, root form unknown).[In some of the verbs of this class the present stem was originally identical with the root; in others the ending -yeo- was added, but has been absorbed by contraction.] But others, as rui-mus (RU), are formed with an additional vowel according to the analogy of the verbs described in d.
NOTE: Some verbs of this class reduplicate the root: as, si-st-e-re (STA, cf. stáre).