How to Conjugate the Irregular Latin Verb Sum "To Be"

The Proper Conjugations of Esse

Graffiti reading "civis romanus sum"
"I am a Roman citizen." A proud graffito on via dell'Umiltà.

 CC BY 2.0 by antmoose

The Latin word sum is perhaps among the best known of all the Latin verbs and it is among the hardest to learn. Sum is the present indicative tense of the verb esse, meaning "to be." As with many other living and dead languages, esse is one of the oldest verb forms in Latin, one of the most frequently used of the verbs, and one of the most irregular verbs in Latin and related languages. It is also often contracted in casual use (such as in English I'm, that's, they're, he's), so that the verb is almost invisible to the listener.


The progenitor form of "to be" is in the Proto-Indo-European (PIE) language, the parent language of Latin, Greek, Sanskrit, Iranian, Germanic, and indeed most of the languages spoken in all of Europe, India, and Iran. Each of the PIE languages has a form of "to be," perhaps because it is so eminently useful: sometimes "to be" can have an existential significance ("To be or not to be," "I think therefore I am"), but also retains its use in everyday language.

In etymological circles, to be is the b-root word, and like all of the b-roots probably is derived from an ancient PIE root, today reconstructed as *h1és-mi (I am). It is also possible that "to be" in Latin derives from the root word *bhuH- meaning "to grow." Other closely related words to esse are asmi in Sanskrit and ešmi in Hittite.

Conjugating Sum

Mood Tense Person Singular Plural
indicative Present First sum sumus
    Second es estis
    Third est sunt
  Imperfect First eram eramus
    Second eras eratis
    Third erat erant
  Future First ero erimus
    Second eris eritis
    Third erit erunt
  Perfect First fui fuimus
    Second fuisti fuistis
    Third fuit fuerunt
  Pluperfect First fueram fueramus
    Second fueras fueratis
    Third fuera fuerant
  Future Perfect First fuero fuerimu
    Second fueris fueritis
    Third fuerit fuerint
Subjunctive Present First sim simus
    Second sit sitis
    Third sit sint
  Imperfect First essem essemus
    Second esses essetis
    Third esset essent
  Perfect First fuerim fuerimus
    Second fueris fueritis
    Third fuerit fuerint
  Pluperfect First fuissem fuissemus
    Second fuisses fuissetis
    Third fuisset fuissent

Irregular Verbs and Compounds

There are several other Latin irregular verbs and compound verbs formed from sum.

Eo - to go Fio - to become
nolo, nolle, nolui - 'to be unwilling' and malo, malle, malui 'to prefer' are similar. Volo - to wish
Fero - to carry Sum - to be
compounds: adsum, desum, insum, intersum, praesum, obsum, prosum, subsum, supersum
Do - to give Edo - to eat


  • Moreland, Floyd L., and Fleischer, Rita M. "Latin: An Intensive Course." Berkeley: University of California Press, 1977.
  • Traupman, John C. "The Bantam New College Latin & English Dictionary." Third Edition. New York: Bantam Dell, 2007. 
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Gill, N.S. "How to Conjugate the Irregular Latin Verb Sum "To Be"." ThoughtCo, Aug. 27, 2020, Gill, N.S. (2020, August 27). How to Conjugate the Irregular Latin Verb Sum "To Be". Retrieved from Gill, N.S. "How to Conjugate the Irregular Latin Verb Sum "To Be"." ThoughtCo. (accessed June 2, 2023).