163. Verbs have regular terminations1 for each of the three Persons, both singular and plural, active and passive.2
a. The Perfect Indicative active has special terminations.3
b. The Imperative has the following terminations.
2. The Passive is an old Middle Voice, peculiar to the Italic and Celtic languages, and of uncertain origin.
3. Of these terminations -ī is not a personal ending, but appears to represent an Indo-European tense-sign -ai of the Perfect Middle. In -is-tī and -is-tis, -tī and -tis are personal endings; for -is-, see § 169.c. Note. In -i-t and -i-mus, -t and -mus are personal endings, and i is of uncertain origin. Both -ērunt and -ēre are also of doubtful origin, but the former contains the personal ending -nt.