3.3 Third conjugation

Overview of Third Conjugation

Third conjugation is one of the largest groups of Latin verbs, and it tends to give students the most trouble. These verbs are identified by the short -ĕ- in their present active infinitive (the second principal part), which ends in -ĕre. That short vowel is what separates them from second conjugation verbs, whose infinitives end in -ēre (with a long -ē-). Getting comfortable with third conjugation patterns is essential because so many common Latin verbs belong here.

Every third conjugation verb builds its forms from three stems: the present stem, the perfect stem, and the supine stem. Each stem generates a different set of tenses and forms, so knowing how to find them is your first step.

Stem Formation

Present stem

To find the present stem, take the second principal part (the infinitive) and remove -ere.

This stem is the base for all present system tenses (present, imperfect, future) in both indicative and subjunctive, plus the present infinitives, present participle, and imperatives.

One thing that trips people up: when you actually conjugate, a thematic vowel (usually -i- or -u-) appears between the stem and the personal endings. This vowel shifts depending on the person and number, which is why third conjugation forms can look different from what you'd expect.

Perfect stem

Take the third principal part and remove the final -ī.

Third conjugation verbs form their perfect stems in several different ways: some add -s- to the present stem (dūc- → dūx-, i.e., dūcs-), some lengthen the stem vowel (ag- → ēg-), some use reduplication (curr- → cucurr-), and others change the stem consonant entirely. There's no single rule, so you need to memorize the third principal part for each verb.

This stem builds all perfect system tenses: perfect, pluperfect, and future perfect (active).

Supine stem

Take the fourth principal part and remove -um.

This stem forms the perfect passive participle ($ductus, -a, -um$), the future active participle ($ductūrus, -a, -um$), and is also used in the passive perfect system (where the participle combines with forms of sum).

Principal Parts

Identifying third conjugation verbs

A third conjugation verb is recognized by its four principal parts. Here's the pattern:

1. First principal part (1st person singular present indicative): ends in -ō (or -iō for -iō verbs)
2. Second principal part (present active infinitive): ends in -ĕre (short -ĕ-)
3. Third principal part (1st person singular perfect indicative): ends in -ī
4. Fourth principal part (supine): usually ends in -um or -sum

For example: dūcō, dūcere, dūxī, ductum (to lead)

The key diagnostic is that short -ĕ- in the infinitive. If you're unsure whether a verb is second or third conjugation, check the vowel length. Your textbook's vocabulary lists and macron markings are your best friend here.

Memorizing principal parts

Because perfect stems are so unpredictable in the third conjugation, memorizing principal parts is unavoidable. A few strategies that help:

• Group verbs by pattern. Verbs that form their perfects the same way are easier to learn together. For instance, dīcō/dīxī, dūcō/dūxī, and scrībō/scrīpsī all use a -s- perfect (which often shows up as -x-).
• Say them aloud in order. Reciting mittō, mittere, mīsī, missum as a rhythmic unit builds muscle memory.
• Use spaced repetition. Flashcard apps (Anki, Quizlet) that space out review sessions are very effective for this kind of rote learning.

Present System

Present tense forms

The present tense uses the present stem plus personal endings, but a thematic vowel appears between them. This vowel changes depending on the form, which is what makes third conjugation tricky. Here's the active indicative of dūcō:

Notice the vowel pattern: -ō, -i, -i, -i, -i, -u. The first person singular has no separate thematic vowel (the -ō absorbs it), and the third person plural uses -u- before -nt. This -u- in the third plural is a hallmark of the third conjugation.

For the passive, replace the active endings with passive personal endings: -or, -eris, -itur, -imur, -iminī, -untur.

Imperfect tense forms

The imperfect is formed by inserting the tense sign -ēbā- between the present stem and the personal endings:

The imperfect describes ongoing, repeated, or habitual action in the past. Translate it as "was/were ___-ing" or "used to ___."

Passive forms use the same -ēbā- tense sign with passive endings: dūcēbar, dūcēbāris, dūcēbātur, etc.

Future tense forms

Here's where third conjugation diverges sharply from first and second conjugation. Instead of -bi- as the future tense sign, third conjugation uses -ē- (and -a- in the first person singular):

The first person singular ends in -am (not -ēm), while all other forms use -ē-. This is a common source of confusion because these forms can look like subjunctive forms of first conjugation verbs. Context and knowing your conjugations will help you tell them apart.

Passive: dūcar, dūcēris, dūcētur, dūcēmur, dūcēminī, dūcentur.

Perfect System

Perfect tense forms

The perfect active uses the perfect stem plus a dedicated set of perfect active endings that are the same across all conjugations:

The Latin perfect can translate as either the English simple past ("he led") or the present perfect ("he has led"), depending on context.

For the perfect passive, Latin uses a compound construction: the perfect passive participle (which agrees with the subject in gender, number, and case) plus the present tense of sum:

Pluperfect tense forms

Add -erā- to the perfect stem, then attach personal endings:

This translates as "had ___-ed" and describes an action completed before another past action.

Passive pluperfect: perfect passive participle + imperfect of sum (ductus eram, "I had been led").

Future perfect tense forms

Add -eri- to the perfect stem (with -erō in the first person singular):

This translates as "will have ___-ed." Watch out: the forms dūxerit and dūxerint look identical to perfect subjunctive forms. Again, context is your guide.

Passive future perfect: perfect passive participle + future of sum (ductus erō, "I will have been led").

Imperative Mood

Present imperative

The present imperative is used for direct commands.

1. Singular (you, one person): take the present stem as-is. For third conjugation, this means removing -ere from the infinitive: dūcere → dūce, regere → rege, mittere → mitte.
2. Plural (you all): add -ite to the present stem: dūcite, regite, mittite.

For negative commands, Latin doesn't just stick nōn in front. Instead, use nōlī (singular) or nōlīte (plural) + the infinitive:

Future imperative

The future imperative is rare in everyday Latin but shows up in legal language and formal/religious texts. It commands someone to do something at a future time or on an ongoing basis.

• 2nd/3rd person singular: stem + -itō (dūcitō)
• 2nd person plural: stem + -itōte (dūcitōte)
• 3rd person plural: stem + -untō (dūcuntō)

You probably won't encounter these often at the elementary level, but it's good to recognize them.

Subjunctive Mood

Present subjunctive

Third conjugation forms the present subjunctive by replacing the thematic vowel with -ā-. Since the present indicative uses -i-/-u- as its thematic vowels, the switch to -ā- is distinctive:

A helpful mnemonic for remembering subjunctive vowels across all conjugations: "wE FEAR A LIAR." The vowels are: ē (1st conj.), a (2nd), a (3rd), a (4th). Third conjugation uses -a-.

Be careful: dūcam (present subjunctive) looks just like dūcam (future indicative, 1st person singular). You'll need to rely on context and clause type to distinguish them.

Imperfect subjunctive

This one has a handy trick: take the entire present active infinitive and add personal endings directly to it.

This works for every conjugation, making the imperfect subjunctive one of the easiest forms to build.

The imperfect subjunctive appears in contrary-to-fact conditions referring to the present ("If he were leading...") and in various subordinate clauses following secondary sequence.

Perfect subjunctive

Add -erī- to the perfect stem (with -erim in the first person singular):

Used in result clauses, indirect questions, and other subordinate clauses in primary sequence when the action is completed.

Passive: perfect passive participle + present subjunctive of sum (ductus sim, ductus sīs, ductus sit, etc.).

Pluperfect subjunctive

Add -issē- to the perfect stem, then personal endings:

This form is used in contrary-to-fact conditions referring to the past ("If he had led...") and in subordinate clauses in secondary sequence for completed action.

Passive: perfect passive participle + imperfect subjunctive of sum (ductus essem, etc.).

Infinitives

Present active infinitive

This is the second principal part itself: -ere added to the present stem.

It functions as a verbal noun and appears in indirect statements, as a complementary infinitive with verbs like possum, and sometimes as the subject of a sentence.

Present passive infinitive

Remove the final -e from the active infinitive and replace it with -ī:

This form appears in indirect statements with a passive meaning and in passive periphrastic constructions.

Perfect infinitives

• Active: perfect stem + -isse → dūxisse (to have led)
• Passive: perfect passive participle (accusative) + esse → ductum, -am, -um esse (to have been led)

Both are used in indirect statements to show that the action of the infinitive happened before the action of the main verb.

Participles

Present active participle

Add -ēns (nominative singular) to the present stem. The genitive singular is -entis, and it declines as a third declension adjective (one termination):

This participle describes action happening at the same time as the main verb. In English, it often translates as "-ing": mīlitēs dūcentēs = "the soldiers leading" or "the soldiers who were leading."

Future active participle

Add -ūrus, -a, -um to the supine stem:

It declines like a regular first/second declension adjective. Combined with forms of sum, it creates the active periphrastic, expressing intention or imminence: ductūrus est = "he is about to lead."

Perfect passive participle

This is the fourth principal part with adjectival endings -us, -a, -um:

It declines like bonus, -a, -um. Besides its role in forming the passive perfect system tenses, it can function as a simple adjective modifying a noun.

Third Conjugation -iō Verbs

Characteristics of -iō verbs

Some third conjugation verbs have an -i- that appears before the personal endings in certain forms. These are called -iō verbs (or "third -iō" / "3rd-iō"). Their principal parts look like this:

Notice that the infinitive is still -ere (short -ĕ-), not -īre, which is how you know they belong to the third conjugation rather than the fourth.

Differences from regular third conjugation

The -i- shows up in specific places:

• 1st person singular present indicative: capiō (not capō)
• 3rd person plural present indicative: capiunt (not capunt)
• Present subjunctive: the -i- is absorbed into the subjunctive -a-, giving capiam, capiās, etc. (these look the same as regular third conjugation subjunctives)
• Present participle: capiēns, capientis
• Imperative singular: cape (the stem vowel is short -e, just like regular third conjugation)
• Present passive infinitive: capī (like regular third conjugation, not capīrī as in fourth conjugation)

The forms where -iō verbs look most like fourth conjugation are the present indicative (especially capiō and capiunt). In the imperfect, future, and perfect system, they behave exactly like regular third conjugation verbs.

Common Third Conjugation Verbs

High-frequency verbs

These are verbs you'll encounter constantly. Memorize their principal parts early:

Irregular verbs

A few third conjugation verbs are highly irregular and need to be learned individually:

• ferō, ferre, tulī, lātum (to bear, carry): The infinitive ferre is contracted, and the perfect and supine stems (tul-, lāt-) come from a completely different root (this is called suppletion).
• fiō, fierī, factus sum (to become, be made): This verb serves as the passive of faciō in the perfect system. Its conjugation is unusual and partly follows third, partly fourth conjugation patterns.

Note: eō, īre (to go) and volō, velle (to wish) are sometimes listed alongside third conjugation irregulars, but they technically belong to their own irregular categories.

Third Conjugation vs. Other Conjugations

Similarities and differences

The perfect system (perfect, pluperfect, future perfect) works identically across all conjugations. Once you know the perfect stem, the endings are always the same. The differences show up in the present system:

• 1st conjugation uses -ā- as its thematic vowel; 2nd uses -ē-; 4th uses -ī-. Third conjugation has no single long thematic vowel, instead using short -i-, -u-, and -e- depending on the form.
• In the future tense, 1st and 2nd conjugation use -bi- (amābit, monēbit), while 3rd and 4th use -ē-/-a- (dūcet, audiet).
• In the present subjunctive, 1st conjugation changes its vowel to -ē-, while 2nd, 3rd, and 4th all use -ā-.

Recognition strategies

When you encounter an unfamiliar verb, here's how to confirm it's third conjugation:

1. Check the infinitive. Does it end in -ĕre (short -ĕ-)? That's third conjugation.
2. Look at the present indicative. Does the 3rd person plural end in -unt (or -iunt for -iō verbs)? Third conjugation.
3. Check the future tense. Does it use -am/-ēs/-et rather than -bō/-bis/-bit? Third conjugation (or fourth).
4. If you're still unsure, the dictionary entry will list the conjugation or you can check the infinitive's vowel length.

Translation Considerations

Tense and aspect

• The perfect tense in Latin covers both the English simple past ("he led") and present perfect ("he has led"). Let the context of the sentence guide your choice.
• The imperfect signals ongoing or repeated past action. Default to "was/were ___-ing" or "used to ___."
• The future and future perfect translate straightforwardly with "will" and "will have."

Voice and mood

• For passive forms, make sure your English translation reflects who is receiving the action: dūcitur = "he/she/it is being led."
• Subjunctive translations depend heavily on the type of clause. In purpose clauses, use "in order to" or "so that." In result clauses, use "that" or "so that." In conditions, use "were" or "had" for contrary-to-fact.
• Participles are flexible in translation. A present participle like dūcēns could be "leading," "while leading," "who was leading," or even "since he was leading," depending on context.