Allen and Greenough's New Latin Grammar, section 165

Heavy Construction

The Allen and Greenough is still under construction; so some links may not work quite the way you would expect.

VERB-ENDINGS.

165.

Every form of the finite verb is made up of two parts:

1. The STEM (see § 24). This is either the root or a modification [QUERY] development of it.

2. The ENDING, consisting of -

1. the Signs of Mood and Tense (see §§ 168, 169).

2. the Personal Ending (see § 163).

Thus in the verb vocá-bá-s, you were calling, the root is VOC, modified into th[QUERY] verb-stem vocá-, which by the addition of the ending -bás becomes the imperfec[QUERY] tense vocábás; and this ending consists of the tense-sign bá- and the personal ending (-s) of the second person singular.