[*] 181. In tenses formed upon the Perfect Stem, v between two vowels is often lost and contraction takes place. [*] a. Perfects in -āvī, -ēvī, -ōvī, often contract the two vowels into ā, ē, ō, respectively: as, amāsse for amāvisse; amārim for amāverim; amāssem for amāvissem; cōnsuērat for cōnsuēverat; flēstis for flēvistis; nōsse for nōvisse . So in perfects in -vī, where the v is a part of the present stem: as, commōrat for commōverat .
[*] Note.--The first person of the perfect indicative (as, amāvī ) is never contracted, the third very rarely.
[*] b. Perfects in -īvī regularly omit v, but rarely contract the vowels except before st and ss, and very rarely in the third person perfect:—- audieram for audīveram; audīsse for audīvisse; audīstī for audīvistī; abiit for abīvit; abiērunt for abīvērunt .
[*] Note 1.--The forms sīris , sīrit, sīrītis, sīrint, for sīveris etc. (from sīverō or sīverim), are archaic.
[*] Note 2.--In many forms from the perfect stem is, iss, sis , are lost in like manner, when s would be repeated if they were retained: as, dīxtī for dīxistī (x = cs); trāxe for trāxisse; ēvāstī for ēvāsistī; vīxet for vīxisset; ērēpsēmus for ērēpsissēmus; dēcēsse for dēcessisse . These forms belong to archaic and colloquial usage.