Sum and Possum: To Be and To Be Able

The verb sum ("I am") is the most important irregular verb in Latin, and possum ("I can") is built from it.

Sum: to be

Person	Latin	English
I	sum	I am
you	es	you are
he/she/it	est	he/she/it is
we	sumus	we are
you (pl.)	estis	you are
they	sunt	they are

Principal parts: sum, esse, fuī.

Using sum

Sum links a subject to a noun or adjective. Both are in the nominative:

• Ego sum Rōmānus. — I am a Roman.
• Puella est pulchra. — The girl is beautiful.
• Rōma est urbs magna. — Rome is a great city.

It also shows location:

• Puer in hortō est. — The boy is in the garden.

Word order with est

The verb est often comes last. In proverbs and short sayings, est is sometimes left out, but here it is present:

• Errāre hūmānum est. — To err is human.

Possum: to be able

Possum is a combination of potis ("able") and sum:

Person	Latin	English
I	possum	I can
you	potes	you can
he/she/it	potest	he/she/it can
we	possumus	we can
you (pl.)	potestis	you can
they	possunt	they can

Principal parts: possum, posse, potuī.

Using possum

Possum is followed by an infinitive:

• Possum vidēre. — I can see.
• Puella cantāre potest. — The girl can sing.
• Nōn possumus manēre. — We cannot stay.

Compounds of sum

Other verbs are compounded with sum:

• absum — I am away, absent
• adsum — I am present
• praesum — I am in charge of

You can see them in English: absent, present, president.

Tips

1. Learn sum and possum in full.
2. Remember the nominative after sum.
3. Use the dictionary to check forms.

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