The Irregular Latin Verb Sum (To Be): Conjugation, Uses, & More

The Latin verb sum (“to be”) is one of the most frequently used words in Latin, but it is also highly irregular. This post covers how to conjugate sum, how to use it, and much more.

I’ll start with a quick overview before diving into the particulars. First and foremost, sum is used to express an equivalence between two things or to describe a noun’s characteristics. This is just like in English, where the verb to be tells us who someone is or what they are like.

In the following examples, forms of the verb to be are in bold.

Līvia est magistra. = Livia is a teacher.

Avēs sunt animālia. = Birds are animals.

Estis altī. = You (all) are tall.

Sum is the second most frequently used word in the Latin language, and this makes sense. We need the verb to be to talk about professions, nationalities, familial relationships, classifications, and so many other aspects of identity.

It’s safe to say that Latin will not make much sense if you don’t understand the verb sum. It is everywhere, from the simplest Latin novellas to the most advanced Roman texts.

The concept is simple, but there is a catch: sum is a highly irregular verb. The forms of to be in Latin often look quite unusual, so it is important to be able to recognize them.

Keep reading to learn all you ever wanted to know about the Latin verb sum (and more)!

How To Conjugate the Latin Verb Sum

Just like all Latin verbs, sum must be conjugated. You have already seen a few conjugated forms in the sample sentences above. For instance, est means “he/she/it is”, while sunt means “they are”.

👉 Need a refresher on conjugation? This post will explain everything.

As with any Latin verb, we will start by looking at the principal parts. The principal parts of sum are sum, esse, fuī, futūrus.

The first two principal parts are different from those of other verbs you may have learned. Normally a verb’s second principal part tells you its conjugation, but esse does not have any of the standard infinitive endings.

This is because sum, esse, fuī, futūrus is an irregular verb. In other words, it does not belong to any of the four Latin verb conjugations.

Sum is highly irregular in the present system (the present, future, and imperfect tenses). But luckily, it is completely regular in the perfect system (the perfect, pluperfect, and future perfect tenses).

In the following sections, I will list all the forms of the verb sum. If you are a beginning student, you may want to stop reading after the present, future, and imperfect tenses and jump down to the section on how to use the verb to be in Latin.

Present System (Indicative)

The present system includes the present, future, and imperfect tenses of the indicative mood. These are usually the first three tenses of sum that students learn.

These are also the most irregular tenses of sum, so you will have to do some memorization. But I do have some good news on that front.

Even in the present system, sum follows the expected patterns for active personal endings. That is, sum ends in m, es ends in s, and so forth.

👉 Not sure what this means? Read all about Latin verb personal endings here!

Now let’s look at the present tense of sum and its translation.

PERSON	SINGULAR	PLURAL
1	sum I am	sumus we are
2	es you are	estis you (y’all) are
3	est he/she/it is	sunt they are

The present infinitive of sum is esse, which means “to be.”

And here is the future tense of sum and its translation:

PERSON	SINGULAR	PLURAL
1	erō I will be	erimus we will be
2	eris you will be	eritis you (y’all) will be
3	erit he/she/it will be	erunt they will be

Finally, here is the imperfect tense of sum and its translation:

PERSON	SINGULAR	PLURAL
1	eram I was	erāmus we were
2	erās you were	erātis you (y’all) were
3	erat he/she/it was	erant they were

And there you go. You have now seen the verb to be in Latin in three crucial tenses.

If you are a beginning student, I recommend that you now skip down to the uses of sum.

In a moment we will move on to the perfect tenses, but first we need to look at the present and imperfect subjunctive.

👉 Wondering what the subjunctive is? Read all about this Latin mood!

Present System (Subjunctive)

The present subjunctive is irregular and consists of sī– plus the active personal endings. The imperfect subjunctive, on the other hand, follows the standard rule: add the active personal endings to the present infinitive.

Here are the forms of the present and imperfect subjunctive. Subjunctives are hard to translate in isolation, but the present tense is something like I may be, you may be, etc. The imperfect tense can be translated as I might be, you might be, etc.

Person	Present	Imperfect
1 sing.	sim	essem
2 sing.	sīs	essēs
3 sing.	sit	esset
1 plur.	sīmus	essēmus
2 plur.	sītis	essētis
3 plur.	sint	essent

Perfect System (Indicative)

The perfect system includes the perfect, pluperfect, and future perfect tenses of the indicative mood, as well as the perfect and pluperfect tenses of the subjunctive.

Fortunately, the perfect system of the Latin verb to be is completely regular. You simply add the appropriate tense and mood endings to the perfect stem.

The perfect stem, as is standard, can be found by removing ī from the third principal part. This means that the perfect stem of sum is fu-.

Here is a conjugation chart showing the perfect indicative of sum:

PERSON	SINGULAR	PLURAL
1	fuī I was / have been	fuimus we were / have been
2	fuistī you were / have been	fuistis you (y’all) were / have been
3	fuit he/she/it was / has been	fuērunt / fuēre they were / have been

And here is the pluperfect indicative of sum:

PERSON	SINGULAR	PLURAL
1	fueram I had been	fuerāmus we had been
2	fuerās you had been	fuerātis you (y’all) had been
3	fuerat he/she/it had been	fuerant they had been

And then the future perfect indicative of sum:

PERSON	SINGULAR	PLURAL
1	fuerō I will have been	fuerimus we will have been
2	fueris you will have been	fueritis you (y’all) will have been
3	fuerit he/she/it will have been	fuerint they will have been

Perfect System (Subjunctive)

Finally, let’s look at the perfect and pluperfect subjunctive. Just like with the perfect tenses of the indicative, you add the regular perfect and pluperfect subjunctive endings to the perfect stem (fu-).

It is hard to translate subjunctive forms in isolation, but the perfect means something like I may have been, you may have been, etc., while the pluperfect is something like I might have been, you might have been, etc.

Person	Perfect	Pluperfect
1 sing.	fuerim	fuissem
2 sing.	fueris	fuissēs
3 sing.	fuerit	fuisset
1 plur.	fuerimus	fuissēmus
2 plur.	fueritis	fuissētis
3 plur.	fuerint	fuissent

Infinitives, Participles, and Imperatives

The verb to be in Latin is highly irregular, as we have seen, but it is also defective. This means that it does not have all of the possible verb forms.

For instance, sum does not have a gerund or a supine. It is also missing some participles and infinitives.

The verb sum has three infinitives:

Tense	Latin Form	Translation
Present	esse	to be
Perfect	fuisse	to have been
Future	futūrum esse / fore	to be about to be

Sum only has one surviving participle: futūrus, a, um “about to be, going to be”. This is a future participle. You can tell this from -ūrus, which is the standard future active participial ending.

Sum has both present imperatives and future imperatives.

Person	Present	Future
2 sing.	es be!	estō be! (you shall be)
3 sing.	none	estō he/she/it shall be
2 plur.	este (y’all) be!	estōte be! (y’all shall be)
3 plur.	none	suntō they shall be

Uses of the Latin Verb Sum (To Be)

Now it’s time to look at concrete examples of the Latin verb to be in action. You will notice that the forms of sum appear at the end, middle, and even beginning of the sentence.

In general, verbs in Latin tend to go at the end of the sentence. But sum is a bit irregular in this regard, too. The word order is highly flexible, so don’t be surprised if you spot the verb to be popping up in unlikely places.

To Be (Linking Verb)

The primary use of the verb sum is as a copula or linking verb. In this context, sum links together and equates two nouns or a noun and an adjective.

Amīca mea est fīlia agricolae. = My friend is the daughter of a farmer.

Hic puer altus erit. = This boy will be tall.

Amāre est bonum. = To love is good.

Poēta esse volō. = I want to be a poet.

We can see sum as an equals sign (=). My friend equals the daughter of a farmer; the boy will equal a tall person.

In such circumstances, the noun or adjective linked by sum (the predicate nominative) needs to be in the same case as the subject. This is typically the nominative case.

Just like the English verb to be, sum can also be followed by a prepositional phrase.

Equus erat in agrō. = The horse was in the field.

Vir rogāvit cūr librī in mēnsā nōn essent. = The man asked why the books weren’t on the table.

Existential Use of Sum

We often think of sum as simply meaning “to be,” but it can also mean “to exist.” Our English verb to be can also have this existential sense, as we shall soon see.

A classic example is René Descartes’ famous phrase:

Cogitō ergō sum. = I think therefore I am / exist.

But this usage shows up in more mundane situations, too. Forms of sum can be the equivalent of English phrases like “there is” and “there are.”

“There” is not translated into Latin. Just the verb is enough.

• est = there is
• sunt = there are
• erit / erunt = there will be
• erat = there was
• erant = there were

Take a look at the following example sentences and note the different ways that sum can be translated into English.

Sunt equī in agrō. = There are horses in the field.

Cūr est canis in sellā? = Why is there a dog on the chair?

Erant quī rēgem nōn amābant. = There were men who did not like the king. = Men existed who did not like the king.

Erit plūs pecūniae post bellum. = There will be more money after the war.

Want more help with Latin?

Join over 1000 email subscribers to hear about new posts and receive exclusive study aids!

​

Send me tips for learning Latin!

We respect your privacy. Unsubscribe at any time. Privacy Policy​

Sum as a helping verb

Sum can act as a helping verb, just like the verb to be can in English.

In English, for instance, you can say “the woman is working.” In this sentence, is isn’t acting as a linking verb or expressing existence. Instead, it is helping to convey the progressive nature of the woman’s action.

Is working is a verbal unit, which we would call the English “present progressive” tense.

Latin does not have a present progressive, but we can find the verb sum used to help create the passive voice of other Latin verbs. The perfect, pluperfect, and future perfect passive tenses are formed with sum and the perfect participle passive.

Here is a quick example with the 1st conjugation verb laudō “praise.” The 1st person singular perfect indicative passive form of laudō is laudātus sum.

On its own, laudātus means “having been praised.” When we combine it with sum, a super literal translation would be “I am having been praised,” i.e. I was praised at some point in the past.

This compound form should be translated as “I have been praised” or “I was praised.” As you can see, sum helps the participle to create the proper meaning.

If you are a beginning student, then you don’t need to worry about this at all yet. If you are more advanced, then be on the lookout for sum in passive forms!

Compound Verbs Built on Sum

The Latin verb to be can also form compound verbs. A prefix (usually a preposition) is added to the beginning of sum in order to change the meaning slightly.

One extremely common compound verb is possum, posse, potuī “be able, can.” It consists of the adjective potis “capable, able” plus sum.

Here are some other compound verbs formed from sum:

Verb	Meaning
absum, abesse, āfuī, āfutūrus	be away, absent (used with ab + ablative)
adsum, adesse, adfuī, adfutūrus	be near, present
dēsum, dēesse, dēfuī, dēfutūrus	be absent, lacking
intersum, interesse, interfuī	be between, present; differ; be of interest
praesum, praeesse, praefuī	preside over (+ dative)
prōsum, prōdesse, prōfuī	be useful, benefit (+ dative)
supersum, superesse, superfuī	remain; abound

The good news is that all of these verbs have the exact same forms as sum, just with the relevant prefix added.

For prōsum, you insert a D between prō and the form of sum if the form begins with E (so, prōdes, prōdest, etc.).

Turris duo mīlia ab urbe abest. = The tower is two miles away from the city.

Mihi pecūnia dēerat. = Money was lacking for me (i.e. I was lacking money).

Hic liber tibi nōn prōderit. = This book will not be useful to you.

Why is the Latin verb sum so weird?

As we have seen, the conjugation of the verb to be in Latin is very irregular. My students often ask me why, and here’s what I tell them.

One cause of the irregularity is the fact that sum is a suppletive verb. Basically, this means that its forms go back to two entirely different roots.

The present system of sum derives from the Proto-Indo-European root *h₁es- or *es- meaning “be”. We see es or just s surviving in the present tense (sum, es, etc.), while in the future (erō, eris, etc.) and the imperfect (eram, erās, etc.) the S has changed to an R between vowels.

The perfect system and the future participle, on the other hand, come from the Proto-Indo-European root *b^huh_x– or *bheu- meaning “become” or “grow.” Eventually, the bh turns into f, and we end up with fuī, futūrus, and all the forms with fu.

The two roots *es- and *bheu- account for a lot of the confusion in the conjugation of sum.

Fun fact: the exact same thing has happened with the English verb to be. Am, are, and is come from *es-, while be, been, and being come from *bheu-. Was and were derive from a third stem, *wes- “remain, dwell.”

You may still be wondering: Why did this bizarre state of affairs occur? Historical linguistics has a lot to say on this topic, but here’s a quick answer. Basically, common words are more likely to be irregular.

Languages change over time, and irregularities in sound and form develop naturally. Over the generations speakers, just as naturally, tend to eliminate the irregularities to make words behave “normally.”

But this standardization does not happen as much with extremely common words. The reason is that speakers hear and use them constantly, so the irregular forms stick around.

The verb sum is the most frequently used verb in the Latin language, so it makes sense that its peculiarities have been preserved.

Frequently Asked Questions about the Latin Verb To Be

Final Thoughts on the Verb To Be in Latin

Do you feel a bit more comfortable with the verb sum and its uses now? I hope so! This irregular verb shows up everywhere in Latin, so you will have lots of opportunities to test your new knowledge.

We have covered a lot of information in this post, so don’t worry if you are feeling overwhelmed. The most important thing to remember is that the verb sum is used in two main ways: first, as a linking verb (“to be”) and second, to express existence (“to exist”).

While you’re here, you may want to take a look at the following posts on learning Latin:

Awesome Resources for Latin Learners

Best Latin Dictionaries for Students

How To Say Happy Birthday in Latin

The Ultimate Guide to Latin Personal Pronouns