Irregular Verbs - Principal Parts and Stems

There are five main irregular verbs in Latin. Of the following, all but fieri form multiple compounds (prefix + verb form), which will be listed out as we learn each verb's details.

Principal Parts

The five verbs have the following principal parts:

sum, esse, fui - to be
eo, ire, ii (ivi), itus - to go
volo, velle, volui - to want
fero, ferre, tuli, latus - to bring, bear
fio, fieri, factus sum - to be made; to become, happen

Irregular Verb Stems

Because these verbs do not belong to a particular conjugation, making them irregular, we find that the stems for these verb forms are also irregular, with some stems being absent or impossible to discern. Please refer to the following chart for a list of all the available stems for these irregular forms.

**Irregular Verbs - Stems**
Irregular Verb	Present Stem	Perfect Stem	Participle Stem
sum, esse, fui	N/A	fui - i = fu-	Perfect Participle: N/A Future Participle: futura - a = futur-
eo, ire, ii (ivi), itus	N/A	ii - i = i- ivi - i = iv-	itus - us = it-
volo, velle, volui	N/A	volui - i = volu-	N/A
fero, ferre, tuli, latus	fero - o = fer-	tuli - i = tul-	latus - us = lat-
fio, fieri, factus sum	fio - o = fi-	N/A	factus sum - us sum = fact-

Nota Bene

For sum, esse, fui, there is a future active participle form:
- futurus, futura, futurum.
- It is possible, then, to form a pseudo-participle stem from this form: futur-.
  - This is not a participle stem in the sense that we have used it in this course, because the participle stem is used specifically to form the perfect participle. It is included here mostly to note the existence of this future participle.
For eo, ire, ii (ivi), itus:
- There are two perfect stems, as there are two 3rd principal parts that were regularly used. Both i- and iv- are correct forms of the perfect stem and are interchangeable. You can select either of these stems when forming verbs in the perfect system active.
- The participle stem can be formed for this verb, but the base verb ire lacks a passive voice. The form itus is available mostly for those compound forms that do allow a passive formation. Its presence in the principal part list, though, does allow us to mark the participle stem for this irregular verb.
For fio, fieri, factus sum:
- The stems are formed, essentially, as a semi-deponent verb would:
  - the present stem is formed like an active present stem from the 3rd-io conjugation (fio - o)
  - there is no perfect stem, like a semi-deponent verb
  - the participle stem is formed like a semi-deponent participle stem (factus sum - us sum)