In Keller's Learn to Read Latin:

In the third principal part of capio, capere, ce(long)pi, caphls, the root vowel changes to a long -e-. The change of the vowel indicates a change in tense. A change in root vowel that corresponds to a change in meaning is called ablaut. This phenomenon is common to all PIE languages. Cf. English sing, sang, sung; song

do, dare, dedi, dams is an irregular first-conjugation verb because its principal parts do not follow the pattern of other first-conjugation verbs, and its present stem, da-, contains a short -a-. However, two forms have -a(long)-: the second person singular present active indicative (dis) and the second person singular present ac- tive imperative (di). (For the indicative see �9; for the imperative see �32.) MEMORIZE THESE FORMS. The third principal part, dedi, is called reduplicated because the first consonant of the root, d-, has been doubled with an intervening vowel. like all verbs of giving, showing, and telling, do regularly takes both a direct object and an indirect object.

Are ablaut and reduplicated phenomena two exceptions that occur during deriving the perfect active stem (obtainable from the third principal part (indicative, active, perfect, singular, first-person form)) from the present stem (obtainable from the second principal part (indicative, active, present, singular, first-person form))?

What are the regular rules that govern the derivation of the perfect active stem from the present stem? Or the deriviation in the other way around?

What are the regular rules that govern the derivation of "the perfect passive stem" (the name I gave to the stem of the fourth principal part, when it is a form of the perfect passive participle) from the present stem or the perfect active stem?


  • 3
    I'm with Cairnarvon on this. Can you explain how these two questions differ?
    – cmw
    Commented May 23, 2023 at 2:11
  • 1
    I agree with the above. Your question is not asking about these two words specifically, but about general rules, and that to me appears to be well covered by the linked question. If, however, you are more interested in specifics about cēpī and dedī, try rephrasing your question. Presently that does not appear to be what you are asking, though.
    – Canned Man
    Commented May 24, 2023 at 18:11

1 Answer 1


I'm afraid there are no regular rules for deriving the perfect stem. That's why it's a principal part: you just have to know what each verb's perfect stem is, as part of learning the verb.

Some ways that particular verbs derive their perfect stem include:

  • Adding -v-: amāre > amāvī "love"
  • Adding -u- to the root: habēre > habuī "have"
  • Adding -s-: scribere > scripsī "write"
  • Reduplicating the first consonant: currere > cucurrī "run"
  • Changing the vowel: agere > ēgī "drive"
  • Lengthening the vowel: vidēre > vīdī "see"
  • Removing an -n-: scindere > scīdī "cut"
  • No change: vertere > vertī "turn"

But there's no reliable way to predict which of these a particular verb will use, and there are even more possibilities, like "change the theme vowel and add v" (petere > petīvī "seek") and "replace it with an entirely different verb" (esse > fuī "be"). You just have to know the perfect stem of each verb as part of your lexicon.

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