A basic introduction to the formation of verb tenses from the four principle parts of a dictionary entry. Note that this section doesn’t explain the roles of verbs, for that you’ll need an introductory Latin grammar book.

Verb Dictionary Entries

A Latin verb dictionary entry gives up to four individual Latin words (or parts of words) and a translation. The four Latin words are called the four principle parts. It looks something like this:

cantō, -āre, -āvī, -ātum to sing/play an instrument

Cantāre—to sing—is a first conjugation verb whose stem doesn’t change over its four principle parts, so the dictionary entry doesn’t waste space by writing it out completely: we just drop the -ō from the first principle part to get cant the common stem. The four principle parts mean the following:

The first principle part is the first-person singluar, present tense: I am singing. If this ends -īo, you’re probably looking at a third-conjugation –īo verb and need to watch out.
The second principle part is the present infinitive: to sing. Its principle job is to tell you what conjugation your verb is; first (-āre), second (-ēre), third (-ere), or fourth (-īre) (there are irregular verbs besides those that fit into the four conjugations!) Be sure to note the macrons in a dictionary entry; without macrons, the present infintives of second and third conjugation verbs look the same.
The third principle part is the first-person singluar, perfect tense: I sang. It shows you how to form the perfect tense forms, but only for the active voice. Drop the -ī from the end to get the stem for the perfect tense. Note that for cantāre, to get the perfect tense stem, we drop the from the first principle part, append the -āvī to get the third principle part, and finally drop the from the end of it. (We can of course just get the stem from the first principle part and add -āv for the same effect.)
The fourth principle part is either the supine (ending in -um) or the perfect passive participle (ending in -us). Either is valid, but we use the supine. Passive voice verb entries are given by dropping either the -um or -us to give the stem

The Perfect Tense

The perfect tense refers to past events, and is the most common tense for doing so. The two tenses in English that it covers are the present perfect (he has done) and the simple past (he did).

Forming the Perfect Tense

To form the perfect tense of a verb, we take the third principle part of our dictionary entry, drop the from the end, and add personal endings:

cantō, -āre, -āvī, -ātum to sing/play an instrument

The perfect tense endings in Latin are unique: all other tenses follow a consistent pattern of endings. The perfect tense endings are as follows:

First I -imus we
Second -istī you -istis you
Third -it he/she/it -ērunt they

Take a quiz on the Perfect Tense!

The Imperfect Tense

The imperfect tense also refers to past events, but those which are incomplete in some sense (hence the im-). Examples of translations for the first person singular imperfect cantābam are:

  • I was singing
  • I began singing
  • I used to sing
  • I sang

Forming the Imperfect Tense

Forming the imperfect tense is slightly more complicated that forming the perfect tense: we need to know the conjugation of the verb before we can begin (see above). The endings showing person and number, however, are consistent across all other tenses.

We begin by looking at the infinitie—the second principle part—of the verb. We then drop the infinitive ending before adding a vowel sound appropriate to each conjugation, as follows:

ConjugationInfinitive EndingVowel Sound
Third -īo-ere-iē-

For cantāre, we drop the –āre and add -ā- to get cantā (note that just dropping the -re only works for first and second conjugation verbs).

This done, we add the imperfect tense indicator -ba-, and add the following verb endings:

First -m I -mus we
Second -s you -tis you
Third -t he/she/it -nt they

(We were slightly economical with the truth; for some tenses the first person singluar ending is . All others stay the same, promise.)

Therefore to find the second person plural imperfect of cantāre, we take our imperfect ‘stem’ cantā, add to it the imperfect marker -ba-, and append to that -tis to get… cantābatis.

Take a quiz on the Imperfect Tense!