177. The Perfect Stem is formed as follows.
a. The suffix v (u) is added to the verb stem,
vocā-v-ī, audī-v-ī
or to the root.
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.
strā-v-ī (sternō, STAR)
sprē-v-ī (spernō, SPAR)
b. The suffix -s- is added to the root.
carp-s-ī (CARP),
tēx-ī (for tēg-s-ī, TEG)2
Note— The modifications of the present stem sometimes appear in the perfect.
fīnx-ī (FIG, present stem fingĕ-)
sānx-ī (SAC, present stem sancī-)
c.reduplicated by prefixing the first consonant—generally with ĕ, sometimes with the root-vowel.
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.
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.
vert-ī (vert-ō)
solv-ī (solv-ō)
f. Sometimes the perfect is formed from a lost or imaginary stem.
petī-v-ī (as if from †peti-ō, †petī-re, PET)