Some adjectives express a complete property by themselves: La ĉambro estas hela. Others invite a complement that identifies a person, topic, source, standard, or proposition: simila al sia patro, fiera pri sia laboro, plena de akvo, certa, ke ŝi venos. The complement belongs semantically to the adjective, not directly to the verb esti.
Esperanto does not have one all-purpose preposition for adjective complements. The relation determines the preposition, and conventional adjective frames must often be learned as units. English is an unreliable guide: English proud of becomes fiera pri, while similar to becomes simila al.
Common adjective frames
| Frame | Core relation | Example |
|---|---|---|
| simila al | comparison or resemblance | simila al sia patrino |
| afabla / fidela / danka al | person toward whom the attitude is directed | danka al la kuracisto |
| fiera / kontenta / certa pri | topic or matter of the state | fiera pri la rezulto |
| plena / libera de | content, source, or absence | plena de akvo |
| grava / utila / danĝera por | affected person, purpose, or intended use | utila por komencantoj |
| riĉa je | possession measured as a feature | riĉa je vitaminoj |
These frames are productive, but the preposition keeps its normal relational meaning. Al points toward a person or standard; pri marks a topic; de can mark content, source, separation, or absence; por identifies a beneficiary or purpose. Je is available where no more specific preposition expresses the relationship cleanly.
Mia nova kolego estas tre simila al sia frato.
My new colleague is very similar to his brother.
Ni estas fieraj pri la laboro, kiun la teamo faris.
We are proud of the work the team did.
La botelo estas plena de malvarma akvo.
The bottle is full of cold water.
The complement follows the adjective in each sentence. A noun after a preposition does not take accusative -n merely because the larger clause contains an object.
One adjective can take more than one relation
Different complements can express different participants. Danka al iu pro io identifies the person who receives thanks with al and the reason with pro. Kolera kontraŭ iu pro io similarly distinguishes the target from the cause.
Mi estas danka al vi pro via rapida respondo.
I am grateful to you for your quick reply.
La loĝantoj estis koleraj kontraŭ la kompanio pro la subita prezaltiĝo.
The residents were angry with the company because of the sudden price increase.
The adjective agrees with what it describes: singular mi → danka, plural loĝantoj → koleraj. The nouns inside al, pro, and kontraŭ phrases follow their own local grammar.
Some adjectives permit alternative frames with a shift of viewpoint. Kontenta pri la rezulto treats the result as the topic of satisfaction; kontenta je sia sorto is an established use of the general preposition je. Both are accepted. For active use, prefer the more transparent specific preposition when it clearly expresses the intended relation.
La kliento ne estis kontenta pri la riparo.
The customer was not satisfied with the repair.
Ĉu vi estas certa pri la adreso?
Are you sure about the address?
The negative and interrogative contexts do not change the adjective-complement frame.
Complements with attributive adjectives
An adjective complement is easiest to process when the adjective is predicative: La studentoj estas fieraj pri sia projekto. It can also appear inside a noun phrase, but the adjective still agrees with the noun it describes.
Ni gratulis la studentojn fierajn pri sia komuna projekto.
We congratulated the students who were proud of their joint project.
Fierajn describes the plural object studentojn, so both take -j-n. The noun projekto follows pri and therefore has neither object -n nor agreement with studentojn.
This postposed construction can be ambiguous: it may sound as though only the proud students were congratulated. If the complement is long or the distinction matters, a relative clause is clearer.
Ni gratulis nur la studentojn, kiuj fieris pri sia komuna projekto.
We congratulated only the students who were proud of their joint project.
Nur makes the subset reading explicit. Esperanto commonly places a comma before a subordinate clause, so the comma alone does not reliably distinguish a restrictive reading from a supplementary one. When the distinction matters, use a quantifier such as nur, supply enough context, or rewrite the sentence.
Placing a heavy adjective-plus-complement before the noun is possible but difficult to process. Instead of la pri la rezulto tre kontenta teamo, prefer la teamo tre kontenta pri la rezulto, or most naturally la teamo estas tre kontenta pri la rezulto.
Clausal complements
An adjective can take a ke-clause that states a fact or proposition. This is common with certa, feliĉa, ĝoja, bedaŭra and evaluative expressions. When a person is the subject, use an A-word agreeing with that person.
Infinitival complements follow a related but distinct controller pattern, covered on Adjectives with Infinitives.
Mi estas certa, ke ŝi sendis la ĝustan dosieron.
I am certain that she sent the correct file.
Ili estis ĝojaj, ke la infanoj revenis sekure.
They were glad that the children returned safely.
When the clause itself is what receives an evaluation, Esperanto normally uses an E-word in an impersonal construction:
Estas grave, ke ĉiuj legu la instrukciojn.
It is important that everyone read the instructions.
Grave evaluates the whole ke-clause. Compare La instrukcioj estas gravaj, where A-word gravaj describes the plural noun. This A/E contrast is part of the regular ending system, not an irregularity.
Scope and substantivization
A complement narrows the adjective's meaning. Libera alone can mean free; libera de eraroj means free from errors; libera por helpi means available to help. The complement determines which relation is asserted.
La raporto estas libera de gravaj eraroj, sed ĝi ne estas preta por publikigo.
The report is free of serious errors, but it is not ready for publication.
If the noun is omitted, an agreeing A-word may remain: la respondecaj pri la projekto means “those responsible for the project,” with an understood plural person noun. This is ellipsis, not a new O-word. Respondeculo is an independent noun meaning a responsible person or person in charge.
— Kiuj devas subskribi? — La respondecaj pri la projekto.
— Who must sign? — Those responsible for the project.
The exchange supplies the human antecedent needed for the elliptical adjective.
Common Mistakes
1. Copying an English preposition
❌ Ŝi estas fiera de sia filino.
Incorrect: fiera normally takes pri for the topic of pride.
✅ Ŝi estas fiera pri sia filino.
She is proud of her daughter.
2. Failing to agree an attributive adjective
❌ Ni renkontis du volontulojn preta por helpi.
Incorrect: preta describes a plural direct object and needs -j-n.
✅ Ni renkontis du volontulojn pretajn por helpi.
We met two volunteers ready to help.
3. Adding accusative inside a prepositional complement
❌ Ili estas kontentaj pri la finan rezulton.
Incorrect: the phrase after pri does not take object -n.
✅ Ili estas kontentaj pri la fina rezulto.
They are satisfied with the final result.
4. Using an A-word to evaluate a whole clause
❌ Estas grava, ke vi venu ĝustatempe.
Incorrect: the ke-clause is being evaluated, so an E-word is required.
✅ Estas grave, ke vi venu ĝustatempe.
It is important that you come on time.
5. Separating the complement from its adjective ambiguously
❌ Ni vidis la pri la rezulto studentojn fierajn.
Incorrectly ordered and hard to parse: pri la rezulto must attach clearly to fierajn.
✅ Ni vidis la studentojn fierajn pri la rezulto.
We saw the students who were proud of the result.
Key Takeaways
An adjective complement completes a relation already opened by the adjective. Learn conventional frames such as simila al, fiera pri, plena de, utila por, and keep the complement close to its adjective. Agreement stays on the adjective; prepositional complements have their own case structure. Use an A-word for a person or noun phrase, but an E-word when an impersonal construction evaluates an infinitive or ke-clause.
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Start learning Esperanto →Related Topics
- Attributive and Predicative AdjectivesA2 — Distinguish adjectives inside noun phrases from adjectives that assert a subject's or object's state, and choose agreement endings accordingly.
- Adjectives with InfinitivesA2 — How adjectives such as preta and kapabla combine with infinitives, and when an impersonal evaluation requires an adverb instead.
- AlA2 — Use al for movement toward a goal, recipients, orientation, and abstract targets without adding an unnecessary accusative ending.
- DeA2 — Use de for movement or development away from a source and for relationships such as possession, authorship, composition, time, and passive agency.
- PriB2 — Use pri to mark a topic, concern, or matter that an action, text, thought, or relationship is about.
- Ke-ClausesA2 — How finite clauses introduced by ke function as statements, subjects, objects, complements, and content descriptions.