Epistemic modality expresses a speaker's judgment about whether a proposition is true: certain, probable, inferred, possible, doubtful, or impossible. Esperanto has no special epistemic verb ending. Instead it combines ordinary indicative tenses with modal verbs such as devi and povi, sentence adverbs such as eble, verŝajne, and certe, and expressions such as ŝajnas, ke. The difficult part is separating a judgment about truth from obligation, permission, hypothetical mood, and the source of one's evidence.
A scale, not a set of exact percentages
The following expressions suggest a rough scale, but they do not encode fixed numerical probabilities.
| Stance | Common Esperanto expression | Typical interpretation |
|---|---|---|
| certainty | certe, sendube | the speaker commits strongly |
| strong inference | devas esti | the evidence makes the conclusion necessary |
| probability | verŝajne, kredeble | more likely than not |
| appearance | ŝajne, laŭŝajne | the available appearance supports the claim |
| possibility | eble, povas esti, ke | the claim remains an open option |
| impossibility | ne povas esti, ke | the claim is ruled out |
Certe la kunveno komenciĝas je la naŭa; mi ĵus kontrolis la programon.
The meeting definitely starts at nine; I just checked the program.
La pordo estas ŝlosita kaj la lumoj estas estingitaj; ili verŝajne jam foriris.
The door is locked and the lights are off; they have probably already left.
Eble la pakaĵo alvenos morgaŭ, sed la livera servo ankoraŭ ne konfirmis la daton.
The package may arrive tomorrow, but the delivery service hasn't confirmed the date yet.
Context, intonation, and the grounds offered by the speaker can move these expressions up or down the practical scale. Verŝajne normally signals probability, but it is not a mathematical claim. Sendube can be sincere, rhetorical, or ironic; irony belongs to pragmatics, not the lexical meaning itself.
Epistemic devi: inference, not duty
With a person and an action, devi often expresses obligation. With a state inferred from evidence, it can express epistemic necessity—the English “must” of deduction.
La kuireja lumo estas ŝaltita; Marta devas esti hejme.
The kitchen light is on; Marta must be home.
La stratoj estas malsekaj, do nokte devis pluvi.
The streets are wet, so it must have rained during the night.
No rule obliges Marta to be home or the rain to fall. The speaker treats those propositions as necessary conclusions from evidence. Compare the deontic reading:
Marta devas esti hejme antaŭ la deka, ĉar ŝiaj gepatroj tiel postulas.
Marta must be home before ten because her parents require it.
The form devas esti is identical. The explanation—evidence in the first example, an imposed rule in the second—selects the reading. When ambiguity matters, use laŭ mia konkludo, ŝajne, or la regulo postulas to state the source explicitly.
To infer an earlier completed event from the present, Esperanto can use a compound infinitive:
Ŝi ne aperis kaj ne respondis al mesaĝoj; ŝi devas esti forgesinta la rendevuon.
She didn't show up and didn't answer messages; she must have forgotten the appointment.
Esti forgesinta locates forgetting before the inferred state. This is accurate but structurally heavy. When no distinction is lost, Ŝi certe forgesis la rendevuon is often clearer. Compound forms are useful tools, not mandatory replicas of English “must have.”
Epistemic povi: open possibility
Povi can say that circumstances permit an event, but it also presents a proposition as possibly true.
La sono povas veni de la ventolilo.
The sound may be coming from the fan.
Povas esti, ke la dosiero estas difektita.
It may be that the file is corrupted.
In povas esti, ke..., the ke-clause is the possible proposition. Esperanto needs no dummy subject equivalent to English “it.” The verb inside the clause takes the tense appropriate to the event and ordinarily remains indicative.
Povas esti, ke ili jam ricevis nian leteron.
They may already have received our letter.
The negative pattern ne povas esti, ke... rules a proposition out:
Ne povas esti, ke la bileto kostas cent eŭrojn; ni certe legis la prezon malĝuste.
The ticket can't cost one hundred euros; we must have read the price incorrectly.
This is epistemic impossibility, not lack of physical ability. The clause subject la bileto belongs inside the proposition.
Adverbs and the indicative
The most economical epistemic markers are sentence adverbs. They can stand initially, next to the focused material, or later in the clause. Initial position makes their scope over the whole proposition especially clear.
Verŝajne ni bezonos pli grandan ĉambron.
We'll probably need a larger room.
La trajno eble malfruos pro la neĝo.
The train may be delayed because of the snow.
Laŭŝajne neniu rimarkis la eraron dum la unua kontrolo.
Apparently nobody noticed the error during the first review.
Eble does not trigger -us. If the speaker considers a future event genuinely possible, the event remains in future -os: eble alvenos. The conditional -us instead frames an event as imagined, dependent, counterfactual, or otherwise non-actual.
Eble ŝi venos, se ŝi finos la laboron ĝustatempe.
Maybe she'll come if she finishes the work on time.
Ŝi venus, se ŝi ne devus labori.
She would come if she didn't have to work.
The first is an open future possibility, so it uses -os. The second is an imagined result, so it uses -us. English “might” can translate either kind depending on context; Esperanto forces the speaker to choose the viewpoint.
The verb endings still form one coherent system
Modal vocabulary does not replace the six regular endings:
| Ending | Function | Modal example |
|---|---|---|
| -i | infinitive, neutral for time/mood | povi erari — to be able to be wrong |
| -as | present reality | povas esti — may be |
| -is | past reality | devis esti — must have been / had to be |
| -os | future reality | eble venos — may come |
| -us | imagined or conditional | povus esti — could be |
| -u | willed or purposed | por ke oni povu kontroli — so that one can check |
The endings never agree with a subject. Mi eble eraras and ili eble eraras use the same finite form. A modal judgment also does not alter valency: legi la raporton still takes la raporton as its object inside eble legis, devas esti leginta, or povas legi.
-u is particularly important to keep separate. It marks a desired action in commands and purpose clauses, not uncertainty about a fact.
Mi sendos klaran mapon, por ke vi povu trovi la lokon.
I'll send a clear map so that you can find the place.
Here the ability to find the place is an intended result. By contrast, Eble vi trovos la lokon merely judges that finding it is possible.
Evidence source is not the same as certainty
Words such as laŭdire “reportedly,” ŝajne “apparently,” and laŭ la prognozo “according to the forecast” indicate where a claim comes from. They do not by themselves establish exactly how strongly the speaker believes it.
Laŭdire la kompanio baldaŭ malfermos novan oficejon, sed ĝi ankoraŭ nenion oficiale anoncis.
Reportedly the company will soon open a new office, but it hasn't officially announced anything yet.
In careful (journalistic) and (academic) writing, naming the source often matters more than selecting a stronger certainty adverb. Laŭ la raporto assigns evidence; certe asserts confidence. They can coexist, but they answer different questions.
See Stance and Evidential Responsibility for source attribution in longer arguments and reports.
Questions and interpersonal restraint
Speakers sometimes use eble or povus to make a question less abrupt. That pragmatic softening should not be confused with a literal uncertainty claim.
Ĉu vi eble scias, kie estas la plej proksima apoteko?
Do you happen to know where the nearest pharmacy is?
Ĉu vi povus kontroli la adreson ankoraŭ unu fojon?
Could you check the address one more time?
The first softens a question about knowledge. The second conventionally functions as a (polite) request, although grammatically it asks about a possible action.
Common Mistakes
Using -us merely because something is uncertain
❌ Eble la gasto alvenus morgaŭ.
Incorrect for an open future possibility stated without any conditional frame — -us makes the arrival non-actual or dependent.
✅ Eble la gasto alvenos morgaŭ.
The guest may arrive tomorrow.
Using -u for a probability judgment
❌ Verŝajne ŝi venu post la tagmanĝo.
Incorrect — -u expresses will or purpose, not probability.
✅ Verŝajne ŝi venos post la tagmanĝo.
She'll probably come after lunch.
Adding English-style esti before a finite modal
❌ Ĝi estas povas esti eraro.
Incorrect — povas is already finite.
✅ Ĝi povas esti eraro.
It may be an error.
Making both verbs finite
❌ La bruo devas venas de la kelo.
Incorrect — the inferred state or action follows devi as an infinitive.
✅ La bruo devas veni de la kelo.
The noise must be coming from the basement.
Treating epistemic devi as obligation
❌ Ĉar la stratoj estas malsekaj, nokte devas havi pluvita.
Incorrect — do not copy English 'must have' with havi plus a participle.
✅ Ĉar la stratoj estas malsekaj, nokte devis pluvi.
Because the streets are wet, it must have rained during the night.
Key Takeaways
- Epistemic modality evaluates truth; it does not automatically impose a duty or create a hypothetical world.
- Devi can mark strong inference, while povi, eble, and povas esti, ke mark possibility.
- Eble and verŝajne normally combine with an indicative tense; uncertainty alone does not require -us.
- State your evidence source separately when responsibility and verification matter.
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Start learning Esperanto →Related Topics
- Devi: Must Or OughtA2 — Use devi for obligation, necessity, expectation, and strong inference, with the right tense, complement, and negative scope.
- Povi: Can Or Be AbleA2 — Use povi with a same-subject infinitive for ability, circumstances, permission, and possibility, including epistemic and polite readings.
- The Conditional in -USA2 — Learn how invariant -us marks imagined and counterfactual situations, polite distance, and conditions without encoding tense.
- Adverbs Modifying Whole ClausesB1 — How sentence adverbs express probability, evaluation, viewpoint, and speaker stance toward an entire proposition.
- Stance and Evidential ResponsibilityB1 — Express opinion, probability, evidence, and information source while making clear how strongly and why you support a claim.
- Ke-ClausesA2 — How finite clauses introduced by ke function as statements, subjects, objects, complements, and content descriptions.