[*] 177. The Perfect Stem is formed as follows:— [*] a. The suffix v ( u ) is added to the verb-stem: as, vocā-v-ī, audī-v-ī; or to the root: as, son-u-ī (sonā-re, root SON), mon-u-ī ( monē-re , MON treated as a root).1
[*] Note.--In a few verbs the vowel of the root is transposed and lengthened: as, strā-v-ī ( sternō , STAR), sprē-v-ī ( spernō , SPAR).
[*] b. The suffix s is added to the root: as, carp-s-ī (CARP), tēx-ī (for tēg-s-ī, TEG).2[*] Note.--The modifications of the present stem sometimes appear in the perfect: as, fīnx-ī (FIG, present stem fingĕ-), sānx-ī (SAC, present stem sancī-).
[*] c. The root is reduplicated by prefixing the first consonant—generally with ĕ, sometimes with the root-vowel: as, ce-cid-ī ( cadō , CAD), to-tond-ī ( tondeō , TOND).[*] Note.--In fid-ī (for †fe-fid-ī, find-ō), scid-ī (for †sci-scid-ī, scindō), the reduplication has been lost, leaving merely the root.
[*] d. The root vowel is lengthened, sometimes with vowel change: as, lēg-ī ( lĕg-ō ), ēm-ī ( ĕm-ō ), vīd-ī ( vĭd-e-ō ), fūg-ī ( fŭg-i-ō ), ēg-ī ( ăg-ō ). [*] e. Sometimes the perfect stem has the same formation that appears in the present tense: as, vert-ī ( vert-ō ), solv-ī ( solv-ō ). [*] f. Sometimes the perfect is formed from a lost or imaginary stem: as, petī-v-ī (as if from †peti-ō, †petī-re, PET).