Esperanto can present an action either as a verb or as a noun. From the action root vizit- come viziti “to visit” and vizito “a visit.” The noun then behaves like any other -o word: it can take article la, plural -j, accusative -n, adjectives, and prepositional complements.
The apparent simplicity hides a real semantic choice. A plain event noun often presents one bounded occurrence or its result; -ad- highlights duration or repetition; -aĵ- often names a concrete product. These meanings are productive, but conventional vocabulary still matters. Esperanto word formation is transparent, not mechanically one-to-one with English endings such as “-ing” and “-tion.”
From an action root to an event noun
With an action-denoting root, -i presents the action as a verb and -o presents it as a noun-like event or manifestation.
| Root | Verb | Event noun | Typical interpretation |
|---|---|---|---|
| vizit- | viziti | vizito | a visit |
| decid- | decidi | decido | a decision or act of deciding |
| eksplod- | eksplodi | eksplodo | an explosion |
| renkont- | renkonti | renkonto | a meeting or encounter |
Niaj najbaroj vizitos nin dimanĉe.
Our neighbors will visit us on Sunday.
La vizito de niaj najbaroj daŭros ĝis la vespero.
Our neighbors’ visit will last until the evening.
The first sentence predicates an action. The second packages that action as an identifiable event, so vizito can take la and a de phrase. The ending -o is a genuine category marker, not a decorative final letter attached to an otherwise complete word.
La subita eksplodo vekis la tutan kvartalon.
The sudden explosion woke the entire neighborhood.
As a noun, eksplodo takes the adjective subita. Compare adverbial modification of a verb: La aparato subite eksplodis “The device suddenly exploded.”
Infinitive clause or event noun?
An infinitive can function as a clause-like subject or complement: Naĝi estas agrable “Swimming is pleasant.” It presents the activity generically and keeps verbal syntax. An event noun presents an occurrence or process as an entity that can be identified, counted, described, or placed in an object role.
Naĝi en la lago estas malpermesite post la deka.
Swimming in the lake is prohibited after ten.
La vespera naĝado en la lago estis trankvila.
The evening swim in the lake was peaceful.
The infinitive naĝi takes the adverbial predicate malpermesite because the subject is an action clause. The noun naĝado takes article la and adjectives vespera, trankvila. English uses “swimming” in both sentences; Esperanto makes the grammatical choice visible.
Do not put la, -j, or -n directly on an infinitive. If you need those noun features, choose an established event noun.
Bounded occurrences and plural -j
A simple action noun without -j commonly denotes one occurrence. Plural -j counts separate occurrences; accusative -n marks their sentence role.
La unua renkonto estis mallonga, sed la postaj renkontoj daŭris pli longe.
The first meeting was short, but the later meetings lasted longer.
Mi neniam forgesos niajn unuajn renkontojn en la malnova kafejo.
I will never forget our first meetings in the old café.
The plural object niajn unuajn renkontojn displays the regular sequence -o-j-n on the noun, with matching -j-n on its adjectives. Event meaning does not create a special declension.
Kiom da vizitoj restas hodiaŭ? — Du, kaj mi jam preparis la ĉambron por ambaŭ.
How many visits remain today? — Two, and I have already prepared the room for both.
Some event nouns can also be understood more abstractly or as activity in context. Countability follows the intended packaging: one decision, several decisions, or decision-making as a general process. The dedicated count and mass meanings page develops that contrast.
-ad- for duration or repetition
The suffix -ad- highlights a sustained course of action or repeated action. Compare krio “one cry,” krioj “several cries,” and kriado “crying, a stretch of repeated or prolonged cries.”
Unu krio venis el la koridoro, poste komenciĝis laŭta kriado.
One cry came from the corridor; then loud shouting began.
La konstruado de la ponto daŭris preskaŭ tri jarojn.
The construction of the bridge lasted almost three years.
Plain konstruo can name the act, undertaking, or result according to context. Konstruado deliberately directs attention to the process over time. -Ad- is therefore not an automatic translation of English “-ing”; add it when duration or repetition is part of what you mean.
An -ad-o noun can itself be plural when several distinct prolonged processes or repeated episodes are counted. That use is grammatical but naturally less frequent than singular process reference.
La du longaj intertraktadoj finiĝis sen interkonsento.
The two prolonged rounds of negotiation ended without an agreement.
Here plural intertraktadoj counts two separately bounded negotiation processes. The presence of -ad- does not block -j.
Event, process, and concrete result
The suffix -aĵ- commonly names a concrete manifestation or product, while -ad- focuses on activity. A plain -o form may cover an event or result if established usage allows it.
| Form | Typical focus | Example meaning |
|---|---|---|
| konstruo | act, undertaking, or result by context | construction |
| konstruado | sustained process | the process of building |
| konstruaĵo | concrete product | a building or constructed object |
La konstruado haltis pro la pluvo, sed la du jam finitaj konstruaĵoj ne estis damaĝitaj.
Construction stopped because of the rain, but the two completed buildings were not damaged.
The distinction is meaningful: stopping an activity is not the same as damaging its products. Similarly, skribo can denote writing as an act or writing system, skribado sustained writing, and skribaĵo a written piece. Conventional meanings must be learned when a form has lexicalized beyond its transparent structure.
Participants and complements
An event noun can retain semantic participants, but it connects them with noun-phrase grammar rather than a verb’s direct-object pattern. De frequently introduces the action’s object or another close relation; an explicit agent can be clarified with fare de.
La konstruado de la nova ponto fare de loka kompanio komenciĝos en Aprilo.
The construction of the new bridge by a local company will begin in April.
Without fare de, two adjacent de phrases can become ambiguous about who builds what. English possessives and “of/by” phrases are equally capable of ambiguity, so name the roles when the context does not settle them.
Participant nouns are a different derivational choice. Konstruanto normally names a person or organization that builds. Esperanto O-participles normally name people participating in an action, so an ordinary nonpersonal product is better called konstruaĵo, not mechanically konstruato. The person rule and the limited technical exceptions are covered separately under substantivized participles.
Common Mistakes
1. Putting an article before an infinitive. An infinitive is not an ordinary -o noun.
❌ La konstrui de la ponto daŭris tri jarojn.
Incorrect — konstrui cannot head a noun phrase with la.
✅ La konstruado de la ponto daŭris tri jarojn.
The construction of the bridge lasted three years.
2. Modifying an event noun with an adverb. Nouns take adjectival modifiers.
❌ La rapide konstruado kaŭzis problemojn.
Incorrect — rapide modifies a verb, not the noun konstruado.
✅ La rapida konstruado kaŭzis problemojn.
The rapid construction caused problems.
3. Forgetting plural and accusative on counted events. Event nouns follow regular noun morphology.
❌ Mi registris du grava renkontiĝo.
Incorrect — two object events require plural and accusative agreement.
✅ Mi registris du gravajn renkontiĝojn.
I recorded two important meetings.
4. Naming a process when the intended referent is its concrete product. Use -aĵ- when the thing produced is central.
❌ La malnova konstruado havas kvindek fenestrojn.
Wrong for the intended meaning ‘building’ — konstruado denotes the building process.
✅ La malnova konstruaĵo havas kvindek fenestrojn.
The old building has fifty windows.
5. Treating -o as inseparable when adding plural and case. Keep the ending sequence visible.
❌ Ni nuligis la vizitonj.
Incorrect — plural -j precedes accusative -n.
✅ Ni nuligis la vizitojn.
We canceled the visits.
Key Takeaways
- An action root plus -o can name an event, occurrence, or conventional result.
- Infinitives keep verbal syntax; event nouns accept articles, adjectives, -j, and -n.
- Simple event nouns often count bounded occurrences, while -ad- highlights duration or repetition.
- -Aĵ- commonly names a concrete product rather than the event that produced it.
- Transparent morphology makes forms interpretable, but dictionaries and attested usage still determine conventional meanings.
Related Topics
- Abstract NounsB1 — How Esperanto names qualities, feelings, actions, and ideas with transparent O-words and meaningful number choices.
- Count and Mass MeaningsA1 — How Esperanto distinguishes countable individuals from unbounded substances and shifts nouns between those meanings.
- The Infinitive in -IA1 — Use the invariant -i form to name an action or state without asserting tense, person, or mood.
- Root Character and CategoryA2 — Understand how a root's inherent meaning shapes its noun, adjective, adverb, and verb forms.
- -ad-: Duration, Repetition, Or Ongoing ActivityB1 — Use -ad- to foreground an action as prolonged, repeated, habitual, or an ongoing process rather than a single event or result.
- -aĵ-: Concrete Manifestation, Product, Or ObjectB1 — Use -aĵ- to name a thing, product, result, or manifestation related to a base, while distinguishing entities from qualities, states, and actions.