In Keller's Learn to Read Latin:

Most verbs of the first conjugation have principal parts that follow the pattern of ambulō, ambulāre, ambulāvī, ambulātum (an intransitive verb) or amō, amāre, amāvī, amātus (a transitive verb). Verbs whose second, third, and fourth principal parts end in -āre, -āvī, -ātus will be identified in the vocabulary list by the notation (1-tr.) following the first principal part. Verbs whose second, third, and fourth principal parts end in -āre, -āvī, -ātum will be identified in the vocabulary list by the notation (1-intr.). No other principal parts will be listed for these verbs.

My understandings and question about the endings of 1st conjugation verbs are:

  • -ā- is the stem vowel, determined by 1st conjugation.
  • -re, -ī, -us or -um are endings of principal parts.
  • How do -v- and -t- appear?

I found more examples across conjugations from the book:

  • 1st conjugation: vocō, vocāre, vocāvī, vocātus
  • 2nd conjugation: moveō, movēre, mōvī, mōtus
  • 3rd conjugation: regō, regere, rēxī, rēctus
  • 3rd i-stem conjugation: capiō, capere, cēpī, captus
  • 4th conjugation: audiō, audīre, audīvī, audītus

and my questions are:

  • Do the fourth principal parts (when being perfect passive participles) always end in -tus, not just in -us? (or in -tum not just in -um, when the verb is intransitive?)

  • After dropping the endings (either -tus or -us, or either -tum or -um), are the remaining parts of perfect passive participles used as stems in forming some forms of verbs? (I haven't found their uses in the book). Are the stems called "perfect passive stems"?



2 Answers 2


The formation of these stems is a complicated issue. There are some papers written on it, but I don't have any at hand. Even though their formation is predictable to a certain, non-negligible extent, the presence of an unpredictable component causes teachers to generally adopt the strategy of advising students to just memorize all of the parts together (like with gender in a language like French or German).

The 3rd principal part

The third principal part is conventionally the first-person singular perfect active indicative. Removing the from the end gives you what can be called the perfect or "perfectum" stem of the verb.

Some common ways it can be formed:

  • the addition of a -v- suffix (after a vowel) or -u- suffix (after a consonant). If a vowel is present, it is often the same as the stem vowel of the present stem (also known as the "infectum" stem), but can sometimes be different.

  • the addition of an -s- suffix (after a consonant; but it often is fused with the preceding consonant, following rules like -ts-, -ds- becoming -ss- or -s- and -gs-, -ks- becoming -x-).

  • reduplication of the first syllable

  • internal lengthening of the vowel

There are other changes that can apply also. These methods are not selected at absolute random: they follow patterns, but the patterns are fairly complicated and there are many exceptions. (I would say it has a similar complexity to plural formation in German, another area where students are commonly told to memorize forms.) Also, a non-negligible number of verbs have no attested perfect stem, and are said to be "defective" in this part (dictionaries either don't list it or list it as a blank line). It is regularly lacking for deponent verbs, since they take passive forms and the perfectum verb tenses are formed periphrastically in the passive.

You can read about some of the patterns in "The cycle without containment: Latin perfect stems", by Donca Steriade (2012).

Here are some quotes:

  • The ā and ī conjugations, with membership in the thousands, use only the v-suffix, the intervocalic variant of –u.

  • The distribution of [...] –s and –u/v is largely predictable. The 110 s-perfect forms in this corpus come from roots ending in consonants; in all cases, these consonants are original obstruents or nasals [...]

  • –s is categorically impossible after vocoids, and essentially impossible after liquids. After stops, the only context where both –s and –u/v are phonotactically permitted, there are twice as many sigmatic than –u/v perfects. This suggests that the default exponent is –s, and that –u/v takes its place only when forced by phonotactics

  • When voicing, place and root-final clusters are also factored in, more details in the selection of perfect morphemes can be predicted: most (23/26) verbs using reduplication target for copy a voiceless stop; half (15/29) of the minority of stop-final roots taking the –u suffix end in [k]; all roots ending in geminate ss or any s//C clusters avoid –s, most for –u, etc.

  • reduplication, unlike –s, –u or μ-affixation, is never a predictable option.

Another way to examine patterns is to look at the size of Wiktionary categories for verbs in the first conjugation, second conjugation, third conjugation and fourth conjugation.

The 4th principal part

The fourth principal part is conventionally the perfect passive participle. It can also be called "the supine stem". Its formation is simpler. The characteristic ending is -tus, but this is regularly replaced with -sus after a stem-final -t- or -d- (which it combines with, forming -ssus after a short vowel or -sus otherwise). The ending -sus also appears irregularly in some other contexts. Aside from the consistent presence of -tus/-sus, there are complications in regard to the presence vs. absence of a preceding vowel and some other ways the stem can potentially be different from the present/infectum stem.

For the majority of verbs, the stem of the fourth principal part is shared among several miscellaneous non-finite formations: the perfect passive participle, the future active participle in -tūrus, abstract fourth-declension nouns in -tus, third-declension nouns in -tiō, agent nouns in -tor/-trix, and some adjectival derivatives (as seen in the word "adjective" itself, from adiectīvus, built on the fourth principal part of adiciō). However, a minority of verbs use slightly different stems for some of these formations.

Prior questions on those minority of verbs:

  • 1
    Thanks. What are the definitions of non-finite formations and finite ones?
    – Tim
    Commented May 22, 2023 at 17:09
  • 1
    @Tim: In Latin, you can recognize a finite verb form by how it inflects for both the person and number of the subject, like "amo", "amas", "amat, amamus, amatis, amant" or "amavi, amavisti, amavit, amavimus, amavistis, amaverunt". The other verb forms are called non-finite, and tend to act similarly to nouns or adjectives; e.g. the infinitives and participles are considered non-finite verb forms.
    – Asteroides
    Commented May 22, 2023 at 17:13
  • 1
    why is it called finite?
    – Tim
    Commented May 22, 2023 at 17:16
  • 2
    @Tim Because it's bound by person and number.
    – cmw
    Commented May 22, 2023 at 18:08

I'll mainly address the question why V and T appear. For a Latin learner working through an introductory book, my answer is that it doesn't matter. (If your interest is linguistic in nature, rather than aimed at learning to read or write Latin, my answer might be irrelevant.)

The whole point of the four or so principal parts of a verb is to collect all the information about the verb so that you can easily find all the forms using them. The first goal is to be able to produce and recognise all forms, given the principal parts. Only after mastering that does it make sense to dig deeper, and by that time you will have picked up a number of patterns and will be able to remember and guess the principal parts of many verbs.

The three (or so) different stems of a verb can look quite different from each other and can end in many ways. The V and T of the regular part of the first conjugation are common but not the only way things can go, not even in the whole first conjugation. I very, very strongly suggest just taking the various stems of each verb as given and focusing on using them. I would guess that that way you'll learn to understand the formation of the various stems faster than by hurrying into it.

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