3.5 Irregular verbs

Types of Irregular Verbs

Latin has a handful of verbs that refuse to follow the standard four-conjugation system. You'll encounter them constantly in reading, so learning their quirks early saves a lot of frustration later.

Common Irregular Verbs

The most important irregular verbs to know are:

• sum, esse, fuī, futūrus (to be): the most common verb in Latin, used on its own and as a linking verb with predicate nominatives
• eō, īre, iī (īvī), itum (to go): has a mix of endings that don't fit neatly into any conjugation
• ferō, ferre, tulī, lātum (to carry/bear): looks like a third conjugation verb in the present, but its principal parts come from completely different roots
• volō, velle, voluī (to want), nōlō (to not want), mālō (to prefer): these three form a family with shared irregularities, especially in the present tense
• possum, posse, potuī (to be able): a compound of pot- ("able") + sum, so its forms shift depending on whether the next letter is s or not (possum but potest)

These verbs appear so often that you'll internalize many of their forms just through reading practice.

Defective Verbs

Some verbs are "defective," meaning they simply don't have a full set of forms. You can only use them in certain tenses or persons.

• inquam (I say): used almost exclusively to introduce direct speech, and mostly in a few specific forms (inquam, inquit, inquiunt)
• meminī (I remember): has only perfect-system forms, but those forms carry present meaning (the perfect meminī translates as "I remember," not "I remembered")
• ōdī (I hate): works the same way as meminī, with perfect forms that translate as present tense

When you see these in a text, don't waste time looking for forms that don't exist.

Impersonal Verbs

Impersonal verbs appear only in the third person singular. They don't have a personal subject the way most verbs do.

• pluit (it rains), ningit (it snows): natural phenomena
• licet (it is permitted), oportet (it is necessary), decet (it is fitting): express obligation or permission

With these verbs, the person affected typically appears in the dative or accusative: licet mihi means "it is permitted to me."

Principal Parts

Every Latin verb has up to four principal parts, and you need them to build every tense and mood. For regular verbs, you can often predict the principal parts from the conjugation. For irregular verbs, you usually can't.

The four principal parts are:

1. First person singular present active indicative (e.g., ferō)
2. Present active infinitive (e.g., ferre)
3. First person singular perfect active indicative (e.g., tulī)
4. Supine / perfect passive participle (e.g., lātum)

From part 1, you get the present stem. From part 3, you get the perfect stem. From part 4, you get the participial stem. If any of these are irregular, every tense built on that stem will be affected.

Irregular Principal Parts

Here's what makes irregular verbs tricky: their principal parts can look nothing like each other.

Notice that ferō uses three entirely different roots across its principal parts. This is called suppletion (more on that below). Meanwhile, volō and possum lack a fourth principal part entirely.

Memorization Techniques

• Group verbs with similar patterns together. For instance, volō, nōlō, and mālō share many of the same irregularities.
• Use spaced repetition (flashcards, apps like Anki) to drill principal parts until they're automatic.
• Practice in sentences, not in isolation. Seeing tulī in context ("servus aquam tulī" → "the slave carried water") makes it stick better than memorizing a list.

Conjugation Patterns

Even though these verbs are "irregular," many of them still use the same personal endings as regular verbs. The irregularity is usually in the stem, not the endings.

Present Tense Irregularities

The present tense is where you'll see the most variation. Here's sum fully conjugated:

Compare that to possum, which attaches pot- (before consonants) or pos- (before s) to the forms of sum:

Once you see the pattern with possum, it becomes predictable: just figure out whether the sum form starts with s or not, and choose pos- or pot- accordingly.

For volō, the present tense has some unusual forms: volō, vīs, vult, volumus, vultis, volunt. The second and third person singular (vīs, vult) are the ones that trip people up.

Perfect Tense Irregularities

In the perfect system, irregular verbs can surprise you with unexpected stems. A few things to watch for:

• Suppletion: ferō becomes tulī in the perfect (a completely different root)
• Reduplication: dō, dare, dedī, datum (to give) doubles the d in the perfect
• Vowel changes: capiō (I take) becomes cēpī in the perfect, with a lengthened vowel

The good news: once you know the third principal part, the rest of the perfect system (pluperfect, future perfect) follows regular patterns. You just add the standard endings to the perfect stem.

Future Tense Irregularities

The future tense of sum is completely irregular and must be memorized:

Since possum is built on sum, its future follows the same pattern: poterō, poteris, poterit, etc.

For eō (to go), the future uses forms like ībō, ībis, ībit, which actually look fairly regular once you know the stem ī-.

Stem Changes

Vowel Changes

Many irregular verbs show vowel shifts between their principal parts. The verb capiō illustrates this well:

• Present stem: capi- (capiō, I take)
• Perfect stem: cēp- (cēpī, I took) — the a lengthens to ē
• Supine stem: capt- (captum) — back to a short a

These shifts aren't random; they often follow patterns of Latin vowel weakening. But at the elementary level, the practical approach is simply to memorize the principal parts.

Consonant Changes

Some verbs alter consonants between forms. For example:

• mittō (I send) → mīsī (I sent): the double tt simplifies to s in the perfect
• scrībō (I write) → scrīpsī (I wrote): the b shifts to ps

These consonant changes often happen at the boundary between the stem and the perfect tense marker.

Suppletive Forms

Suppletion is when a verb uses stems from entirely different roots for different principal parts. This is the most extreme type of irregularity.

The classic example is ferō:

• Present: fer- (from ferō)
• Perfect: tul- (from tulī, a completely different root)
• Supine: lāt- (from lātum, yet another root)

English does this too: "go / went" uses two different roots. There's no trick here other than memorization.

Irregular Verb Groups

-iō Verbs of the 3rd Conjugation

Verbs like capiō (I take) and faciō (I make/do) are sometimes called "3rd conjugation -iō verbs" or "3rd/4th hybrid verbs." They behave like third conjugation verbs in most forms but insert an -i- in certain present-system forms, making them look like fourth conjugation verbs.

Compare:

• Regular 3rd: dūcō, dūcis, dūcit
• 3rd -iō: capiō, capis, capit (note the -iō in the first person, but -is, -it like regular 3rd)

The -i- also shows up in forms like the present subjunctive (capiam) and the present participle (capiēns). These verbs are regular in the perfect system.

Deponent Verbs

Deponent verbs look passive but translate as active. Their forms use passive endings in every tense.

• loquor, loquī, locūtus sum (to speak)
• sequor, sequī, secūtus sum (to follow)

The key thing to remember: when you see passive endings on a deponent verb, translate it actively. Loquitur doesn't mean "he is being spoken" — it means "he speaks."

Deponents still have a few active forms: the present participle (loquēns, "speaking"), the future participle (locūtūrus, "about to speak"), and the gerund.

Semi-Deponent Verbs

Semi-deponent verbs are active in the present system but switch to passive (deponent) forms in the perfect system.

• audeō, audēre, ausus sum (to dare): present forms are normal active (audeō, audēs, audet), but the perfect uses the passive participle + sum (ausus sum = "I dared")
• gaudeō, gaudēre, gāvīsus sum (to rejoice)
• soleō, solēre, solitus sum (to be accustomed)

When translating, treat all their forms as active regardless of which system they're in.

Frequency and Usage

High-Frequency Irregular Verbs

The irregular verbs you'll see most often are sum, possum, ferō, eō, volō, faciō, and dō. These appear on nearly every page of Latin you'll ever read. Prioritize these above all others.

Sum in particular does double duty: it works as a standalone verb meaning "I am/exist" and as an auxiliary in compound tenses (like amātus est, "he was loved").

Context-Specific Usage

Some irregular verbs have meanings that shift depending on context:

• fīō, fierī, factus sum serves as the passive of faciō. So faciō means "I make" (active), and fīō means "I am made" or "I become."
• inquam appears almost exclusively to introduce direct quotations, similar to English "said."
• ferō can mean "carry," "bear," "endure," or "report" depending on context.

Idiomatic Expressions

Several common Latin phrases are built around irregular verbs:

• licet mihi = "it is permitted to me" (dative + impersonal verb)
• mihi placet = "it pleases me" / "I decide"
• mē oportet = "it is necessary for me" / "I ought" (accusative + impersonal verb)

Pay attention to which case the person takes with each impersonal verb. Licet takes the dative, while oportet takes the accusative.

Comparison with Regular Verbs

Similarities in Endings

Even highly irregular verbs usually keep the standard personal endings: -ō/-m, -s, -t, -mus, -tis, -nt for active, and -r, -ris, -tur, -mur, -minī, -ntur for passive. The irregularity is almost always in the stem, not the ending.

This means that if you can identify the stem of an irregular form, you can still parse person, number, and voice the same way you would for any regular verb.

Differences in Stems

Where regular verbs have predictable stem formation (chop off -re from the infinitive, etc.), irregular verbs may:

• Use completely different roots for different principal parts (suppletion)
• Have unpredictable vowel or consonant changes
• Lack certain forms entirely (defective verbs)

The practical takeaway: you can't reliably "figure out" an irregular verb's forms from one principal part. You need to know all of them.

Study Strategies

• Make comparison charts that put a regular verb next to an irregular one in the same tense. Seeing amō, amās, amat next to sum, es, est highlights exactly where the irregularity lies.
• Conjugate out loud. Writing and saying the forms builds muscle memory.
• When you encounter a new irregular form in reading, look it up immediately and note which principal part it comes from. This builds your recognition over time.

Common Mistakes

Overgeneralization Errors

The most frequent mistake is treating an irregular verb like a regular one. For example, students sometimes try to form the perfect of ferō as ferī instead of the correct tulī, because they're applying regular third conjugation patterns.

To avoid this: whenever you encounter a verb, check whether it's irregular before you start conjugating it.

Confusion with Regular Forms

Some irregular forms look deceptively similar to regular forms of other verbs. For instance, est (from sum, "he/she is") could be confused with est (from edō, "he/she eats") in certain contexts. Context and the rest of the sentence will usually make the meaning clear.

Tense and Mood Errors

Watch out for these specific traps:

• Confusing the future of sum (erō) with the perfect (fuī). They look nothing alike, but students sometimes mix up which is which.
• Forgetting that meminī and ōdī have perfect forms with present meanings. If you translate meminī as "I remembered" instead of "I remember," you'll get the tense wrong.
• Misforming compound tenses by using the wrong form of sum as the auxiliary.

Translation Challenges

Identifying Irregular Forms

When you hit a verb form you don't recognize, consider whether it might be an irregular verb before assuming you've found a new vocabulary word. A form like tulērunt might look unfamiliar until you realize it's the perfect of ferō (third principal part tulī + perfect ending -ērunt).

Build the habit of checking your irregular verb charts when a form doesn't parse normally.

Contextual Interpretation

Surrounding words give you strong clues. If you see a nominative subject and an accusative object with an unrecognized verb form between them, you can deduce it's likely an active transitive verb. That narrows down your options considerably.

For impersonal verbs, look for a dative or accusative noun nearby that tells you who is affected, and an infinitive that tells you what the action is: licet mihi abīre = "it is permitted to me to leave" = "I may leave."

Translating into Natural English

Latin irregular verbs don't always map neatly onto single English words. A few tips:

• possum + infinitive translates as "can" or "am able to": vidēre possum = "I can see"
• volō + infinitive translates as "want to": īre volō = "I want to go"
• Impersonal constructions often sound more natural in English when you make the dative/accusative person into the subject: licet mihi → "I am allowed" rather than "it is permitted to me"