A subordinate clause has its own subject and its own finite verb. Choose that verb's -as, -is, -os, -us, or -u ending from the time and mood of the subordinate situation. Esperanto does not require the subordinate verb to copy the main verb, and it does not import English rules that hide future time behind a present form.
These endings never vary with person or number. -as, -is, -os are real-tense forms; -us and -u mark imagined and volitive meanings without tense. The infinitive -i is likewise tenseless and nonfinite, so it does not head an ordinary subordinate clause with its own grammatical subject. Subordination also leaves valency intact: a verb that takes an object or another complement still takes it inside the subordinate clause.
Treat the subordinate proposition as a small sentence
A useful diagnostic is to remove the introductory word and imagine the clause as an independent sentence. If the independent proposition would be La pordo estas ŝlosita, a factual ke-clause normally keeps estas.
Mi vidas, ke la pordo estas ŝlosita.
I see that the door is locked.
Mi vidis, ke la pordo estis ŝlosita.
I saw that the door was locked.
Mi vidos, ĉu la pordo estos ŝlosita.
I will see whether the door will be locked.
The verbs do not agree mechanically. In each example, the subordinate form locates the door's state within the intended scene. The ĉu-clause in the third sentence is an indirect yes/no question; ĉu changes the clause's function, not its tense system.
Future time remains future after temporal conjunctions
English uses a present form after “when,” “as soon as,” “before,” “after,” and “until” even when the subordinate event is future. Esperanto marks the actual future with -os.
Kiam la gasto alvenos, ni komencos vespermanĝi.
When the guest arrives, we will start dinner.
Mi skribos al vi tuj kiam mi scios la rezulton.
I will write to you as soon as I know the result.
Ni kontrolos ĉiujn fenestrojn antaŭ ol ni foriros.
We will check all the windows before we leave.
Post kiam la infanoj endormiĝos, ni povos trankvile paroli.
After the children fall asleep, we will be able to talk quietly.
Mi atendos ĉi tie, ĝis vi revenos.
I will wait here until you return.
Both main and subordinate events are future, so both normally take -os. A present form is correct only if the subordinate situation is genuinely present or generally valid.
Mi telefonos al Ana, kiam mi havos ŝian numeron.
I will call Ana when I have her number. (future possession)
Mi telefonos al Ana, ĉar mi havas ŝian numeron.
I will call Ana because I have her number. (present possession)
The conjunction does not assign tense by itself; meaning does.
Simultaneous and ordered past events
Past subordinate clauses likewise use -is when their situations belong to the past scene. Conjunctions specify overlap or sequence.
Dum mi preparis la supon, Leo tranĉis la panon.
While I was preparing the soup, Leo cut the bread.
Kiam mi malfermis la pordon, la telefono sonoris.
When I opened the door, the phone rang.
Post kiam ni finis la kunvenon, ni iris por kafo.
After we finished the meeting, we went for coffee.
Esperanto simple uses -is for ongoing background, bounded events, and anterior events. Dum signals sustained overlap; kiam identifies a time or intersection; post kiam orders two events. Heavy participial tenses are unnecessary when the conjunction already makes the relationship clear.
The conjunction ĝis introduces an endpoint and should normally contain an event that can establish that endpoint.
Ni restis en la kafejo, ĝis la pluvo ĉesis.
We stayed in the café until the rain stopped.
Ĝis la pluvo ĉesis is clearer than a clause that merely describes an ongoing state. For “until he fell asleep,” use ĝis li ekdormis, not ĝis li dormis, because the onset ends the waiting.
Real conditions versus imagined conditions
A se-clause describing a genuinely open condition uses the real tense appropriate to its time.
Se ŝi havas la ŝlosilon, ŝi povas eniri nun.
If she has the key, she can enter now.
Se morgaŭ neĝos, ni laboros hejme.
If it snows tomorrow, we will work from home.
Use -us when the condition is presented as imagined, contrary to fact, or remote rather than simply uncertain.
Se ŝi havus la ŝlosilon, ŝi povus eniri.
If she had the key, she could enter.
The contrast is mood, not time. Havus does not mean past. Context might make the imaginary possession present, future, or even past. See the conditional in -us for the full range.
Factual ke versus wanted ke
After verbs of knowing, seeing, stating, or discovering, a ke-clause typically asserts or reports content and uses a real tense.
Ni eksciis, ke la muzeo estos fermita lunde.
We learned that the museum will be closed on Monday.
After verbs and expressions of request, desire, necessity, purpose, or influence, the subordinate action is not asserted as fact; it is wanted. Use -u.
La administranto petis, ke ni foriru antaŭ la sesa.
The manager asked us to leave before six.
Necesas, ke ĉiuj subskribu la liston.
Everyone needs to sign the list.
Mi parolas mallaŭte, por ke la bebo ne vekiĝu.
I am speaking quietly so that the baby does not wake up.
English often uses an infinitive, a modal, or a plain present in these meanings. Esperanto -u consistently marks the subordinate action as willed or purposed. It is not a future tense and does not become -is after a past main verb.
Hieraŭ ŝi petis, ke mi venu hodiaŭ.
Yesterday she asked me to come today.
The asking is factual past -is; the requested coming is volitive -u.
Relative clauses choose their own time
A relative clause describes its antecedent and independently locates the described event.
Mi serĉas la dosieron, kiun vi sendis hieraŭ.
I am looking for the file that you sent yesterday.
Jen la ĉambro, en kiu ni laboros morgaŭ.
Here is the room in which we will work tomorrow.
Mi bezonas programon, kiu funkcias sen interreto.
I need a program that works without an internet connection.
Present serĉas does not force present sendas; present jen does not block future laboros. In the third example, funkcias describes a current or general property.
Reported content is a special viewpoint
Genuine indirect speech or thought follows the preservation rule: it retains the form of the original message rather than measuring everything from the later narrator's present.
Li diris, ke li venos vendrede.
He said that he would come on Friday.
This keeps his original Mi venos vendrede. It is a special discourse relation, explained fully in relative time without sequence-of-tense backshift. Do not generalize it to every clause introduced by ke.
Common Mistakes
Copying English present after future kiam
❌ Mi montros al vi la foton, kiam vi venas.
Incorrect for a future visit — the subordinate event also needs -os.
✅ Mi montros al vi la foton, kiam vi venos.
I will show you the photo when you come.
Using -us for an open future condition
❌ Se la vetero pliboniĝus morgaŭ, ni iros al la lago.
Incorrect for a genuinely possible forecast-based condition — the mixed mood obscures the intended real scenario.
✅ Se la vetero pliboniĝos morgaŭ, ni iros al la lago.
If the weather improves tomorrow, we will go to the lake.
Using factual tense for a requested action
❌ Ŝi petis, ke mi sendis la kvitancon.
Incorrect — this says neither a clear past fact nor the requested action.
✅ Ŝi petis, ke mi sendu la kvitancon.
She asked me to send the receipt.
Adding kiam after temporal ĝis
❌ Atendu, ĝis kiam mi revenos.
Incorrect as a simple temporal endpoint — ĝis already introduces the clause.
✅ Atendu, ĝis mi revenos.
Wait until I return.
Ĝis kiam is correct in an indirect question such as Mi ne scias, ĝis kiam ili restos “I don't know until when they will stay.”
Adding negative ne inside an affirmative endpoint
❌ Mi ne foriros, ĝis vi ne respondos.
Incorrect for 'until you answer' — the extra ne reverses the endpoint clause.
✅ Mi ne foriros, ĝis vi respondos.
I will not leave until you answer.
Key Takeaways
- Every subordinate finite verb expresses its own time and mood relation.
- Future events keep -os after kiam, ĝis, antaŭ ol, post kiam, and in real future se-clauses.
- -us marks an imagined condition; -u marks a wanted or purposed action.
- Conjunctions such as dum, kiam, and post kiam organize past relations without requiring compound tenses.
- Indirect speech preserves an original viewpoint, but ordinary factual subordinate clauses use the narrator's timeline.
Related Topics
- Relative Time without Sequence-of-Tense BackshiftA2 — Preserve the original verb form in reported speech and thought instead of applying English-style tense backshift.
- The Present in -ASA1 — Use -as for actual situations in progress, current states, habits, and generally valid statements.
- The Past in -ISA2 — Use -is for actual actions and states before the relevant present, regardless of whether they were completed, ongoing, habitual, or earlier than another past event.
- The Future in -OSA2 — Use -os for actions and states expected after the relevant present, including in time and condition clauses where English uses a present form.
- The Volitive in Subordinate ClausesA2 — Learn when Esperanto uses -u in ke- and por ke-clauses to express a request, purpose, intended result, or other desired action.
- The Conditional in -USA2 — Learn how invariant -us marks imagined and counterfactual situations, polite distance, and conditions without encoding tense.