The Irregular Latin Verb Possum (To Be Able): Conjugation & Uses

The verb possum “to be able” appears frequently in Latin, but it is also very irregular. Keep reading to learn how to conjugate – and use – possum.

Possum is used to talk about ability, possibility, and power. This is your go-to verb to express what you can and cannot do, whether you are referring to physical or intellectual (in)ability or to some external constraint.

Hoc saxum portāre possum. = I can / I am able to carry this rock.

Rōmam īre nōn possum; rēx erit īrātus. = I cannot / I am not able to go to Rome; the king will be angry.

We will discuss the usage of possum in more detail later on. And don’t worry, there will be many more example sentences!

Before we go any further, I want to clarify one thing. Possum is built off the verb sum (“to be”), and in this post I will assume that you have already learned about sum.

👉 Not familiar with sum? Read this post about the most common Latin verb.

Still with me? All right. Time to learn everything you need to know about possum!

How to conjugate the Latin verb possum

When learning a new Latin verb, you should always take a look at the principal parts. The principal parts of possum are possum, posse, potuī.

Possum lacks a fourth principal part, and the first two principal parts look unusual. Usually, the second principal part indicates the verb’s conjugation, but that won’t work here.

This is because possum is an irregular verb. It does not belong to any of the four Latin verb conjugations.

The verb possum is a contracted form of potis sum, “I am able.” The adjective potis, e – which means “able, capable, possible” – was rarely used in Classical Latin on its own, but it survived in abbreviated fashion in possum.

Potis sum “I am able” became potsum and then possum. Potis es “you are able” became potes. And so forth. As you can see, possum depends on the verb sum for these present tense forms.

It turns out that the present system of possum is irregular, but based on sum. The perfect system, on the other hand, is entirely regular and thus is not based on sum.

Let’s look at the concrete conjugations, and you will see what I mean.

Present System (Indicative)

The present system of possum is entirely built off sum. This is good news, because it means that if you have already memorized the conjugation of sum, it will be easy to learn the conjugation of possum.

The present system includes the present, imperfect, and future indicative tenses. To conjugate possum in each of these tenses, simply add pos– or pot– onto the beginning of sum.

You add pos– if the form of sum begins with S, and pot– if it begins with E.

Here is the present indicative of possum along with its translation:

PERSON	SINGULAR	PLURAL
1	possum I am able, I can	possumus we are able, etc.
2	potes you are able, you can	potestis you (y’all) are able, etc.
3	potest he/she/it is able, etc.	possunt they are able, etc.

Possum also has a present infinitive, posse. Posse means “to be able.”

Here is the future indicative of possum:

PERSON	SINGULAR	PLURAL
1	poterō I will be able	poterimus we will be able
2	poteris you will be able	poteritis you (y’all) will be able
3	poterit he/she/it will be able	poterunt they will be able

Finally, here is the imperfect indicative of possum:

PERSON	SINGULAR	PLURAL
1	poteram I was able, I could	poterāmus we were able, etc.
2	poterās you were able, you could	poterātis you (y’all) were able, etc.
3	poterat he/she/it was able, etc.	poterant they were able, etc.

That wasn’t so bad, was it? All of these forms come directly from sum.

If you are a beginning student, you may wish to stop reading here and jump down to the uses of possum. If you are in the intermediate or advanced stage, keep reading to learn about the perfect system and the subjunctive tenses.

Present System (Subjunctive)

The present system also includes the present and imperfect subjunctive. The present subjunctive of possum is simply the present subjunctive of sum with an initial pos-.

The imperfect subjunctive actually follows the standard rules: add the active personal endings to the present infinitive. In this case, the present infinitive is posse (which is based on esse, the present infinitive of sum).

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 able, you may be able, etc. The imperfect tense can be translated as I might be able, you might be able, etc.

Person	Present	Imperfect
1 sing.	possim	possem
2 sing.	possīs	possēs
3 sing.	possit	posset
1 plur.	possīmus	possēmus
2 plur.	possītis	possētis
3 plur.	possint	possent

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.

Possum is totally regular in the perfect system, both in the indicative and in the subjunctive. You simply add the appropriate endings to the perfect stem, potu-.

(Remember: you find the perfect stem of a Latin verb by removing –ī from the third principal part.)

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

PERSON	SINGULAR	PLURAL
1	potuī I was / have been able, I could	potuimus we were / have been able, etc.
2	potuistī you were / have been able, you could	potuistis you (y’all) were / have been able, etc.
3	potuit he/she/it was / has been able, etc.	potuērunt / potuēre they were / have been able, etc.

And here is the pluperfect indicative of possum:

PERSON	SINGULAR	PLURAL
1	potueram I had been able	potuerāmus we had been able
2	potuerās you had been able	potuerātis you (y’all) had been able
3	potuerat he/she/it had been able	potuerant they had been able

And then the future perfect indicative of possum:

PERSON	SINGULAR	PLURAL
1	potuerō I will have been able	potuerimus we will have been able
2	potueris you will have been able	potueritis you (y’all) will have been able
3	potuerit he/she/it will have been able	potuerint they will have been able

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 (potu-).

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

Person	Perfect	Pluperfect
1 sing.	potuerim	potuissem
2 sing.	potueris	potuissēs
3 sing.	potuerit	potuisset
1 plur.	potuerimus	potuissēmus
2 plur.	potueritis	potuissētis
3 plur.	potuerint	potuissent

Infinitives & Participles?

Possum is an irregular verb, as we have seen. But it is also defective. This means that it does not have all of the possible infinitive and participial forms. There are no imperatives, and the gerund and supine are also missing.

Possum has two infinitives.

• posse = to be able (present infinitive)
• potuisse = to have been able (perfect infinitive)

Possum only has one participle: potēns, potentis, a present participle meaning “able, powerful”. While potēns is technically a participle, it is commonly used as an adjective.

👉 Curious about participles? Read more about Latin participles here.

How to use the Latin verb possum

As I mentioned at the very beginning of this post, possum means “be able to” or “can.” It tells us what people are able (or not able) to do and what is possible (or impossible).

From a grammatical perspective, the main thing to remember is that this verb appears extremely frequently with a complementary infinitive.

A complementary infinitive complements or completes the meaning of possum. It tells you what you are able to do, thus finishing the thought.

Consider the following sentence:

Tibi vēritātem dīcere possum. = I can tell you the truth.

In this sentence, dīcere is the complementary infinitive. It explains what I am able to do: tell the truth.

In the following examples, I have put both the form of possum AND the complementary infinitive in bold.

Most of the time you see a form of the Latin verb possum, there will be an infinitive somewhere near it.

Possum can also appear independently without an infinitive (although this is less common). On its own, the verb can mean “have power”, “be powerful,” or “have influence.”

The exact translation depends on the sentence in question, so here are a few examples from ancient Roman texts. Notice how potest can mean “it is possible” in Sentence #3.

If this independent use of possum confuses you, don’t worry. It is much more common to see possum with an infinitive, so that is what you should focus on at first.

If you see a form of possum on its own, start by trying to translate it as “be able” or “be powerful” and see if that makes sense. With time, you will get used to the different uses!

Derivatives of possum

The Latin verb possum has many descendants in modern Romance languages and in English. I will mention some of these derivatives below, because I find them helpful in remembering the various forms of possum (and its meaning).

Some derivatives have poss– in them; this reminds us of the present system of possum.

• possible
• impossible
• possibility
• posse

Other derivatives have pot-. This reminds us of possum‘s origin in the adjective potis and it can help you remember the T that shows up in the perfect system.

• potent
• potential
• potency
• omnipotent
• impotent

Possum has also given us other words, such as the Spanish poder, poderoso, posible, etc. and French pouvoir, puissante, etc.

I hope that these derivatives will help you remember possum a bit better!

The Latin Verb Possum: Final Thoughts

The verb possum is the 2nd most common verb in the Latin language (coming just after sum). This means that it is very important to understand how it works.

This post has covered how to conjugate and use this extremely frequent verb. Remember the following two facts, and you will be in good shape:

1. Forms of possum are built off forms of sum
2. Forms of possum usually appear along with a complementary infinitive that explains what you are able to do

How do you feel about possum? I have confidence in you. Tū potes linguam latīnam discere! (You can learn Latin!)

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