English often uses “you” for any person: “You never know,” “You pay at the counter,” “When you get older...” Neutral Esperanto uses oni for that generic meaning. Vi refers to the actual person or people being addressed, whether one or several.
The contrast is pragmatic as well as grammatical. Oni presents a statement as generally true or applicable to an unspecified person. Vi turns it toward the listener: the advice, prediction, or obligation applies to you.
Oni means an unspecified person or people
Oni is a standard third-person personal pronoun. It can mean “one,” generic “you,” “people,” or impersonal “they,” depending on natural English style.
En tiu restoracio oni pagas ĉe la kaso.
At that restaurant, you pay at the counter.
Oni neniam scias, kio okazos morgaŭ.
You never know what will happen tomorrow.
En Esperanto oni skribas la vortojn tiel, kiel oni prononcas ilin.
In Esperanto, words are written as they are pronounced.
No particular addressee is responsible for these actions. The sentences describe a custom, a general human limitation, and a language-wide practice.
English translation need not preserve the word “one.” Oni neniam scias is grammatically closer to “one never knows,” but idiomatic English normally says “you never know.” Translate the meaning, not the surface pronoun.
Vi addresses the listener
Use vi when the current addressee is genuinely included as the person expected to act, experience, or decide.
Se vi premas ĉi tiun butonon, la ekrano estingiĝos.
If you press this button, the screen will turn off.
Vi devas montri vian bileton antaŭ ol eniri.
You must show your ticket before entering.
The first sentence is an instruction to the person using the device. The second places an obligation on the listener. Compare a genuinely general statement:
Se oni tro longe rigardas ekranon, la okuloj laciĝas.
If you look at a screen for too long, your eyes get tired.
Here the claim concerns people generally. Changing oni to vi would turn health information into a statement specifically about the addressee's behavior.
In conversation, a speaker may deliberately use vi to make general advice vivid and personally relevant. That is direct reader/listener address (informal), not the neutral generic-pronoun system. For international clarity, use oni when no actual addressee is intended.
Oni has object and possessive forms
As a personal pronoun, oni forms regular onin for a direct object and onia for an unspecified person's possessive relation. Both are standard but much less frequent than subject oni.
Tia longa atendado povas lacigi onin.
Such a long wait can tire one out.
Onia opinio povas ŝanĝiĝi post nova sperto.
One's opinion can change after a new experience.
Onin carries object -n. Onia is useful here because it belongs to the subject phrase onia opinio. English may translate either with generic “you/your.”
When oni is the subject and another expression refers back to that same generic person, use reflexive sin/sia, not onin/onia.
Oni devas kunporti sian identigilon.
One must bring one's identification.
Oni foje demandas sin, ĉu la peno valoras.
One sometimes asks oneself whether the effort is worthwhile.
Sian and sin point back to subject oni. The same clause-bound reflexive rule used with li, ŝi, and ili applies here.
Number and agreement with oni
Oni may refer semantically to people in general, but neutral grammar usually treats it as singular for predicative agreement.
Post longa vojaĝo oni ofte estas laca.
After a long journey, you are often tired.
Use laca, not lacaj, unless an exceptional context deliberately foregrounds a plural interpretation. The verb itself never changes for person or number: oni estas, vi estas, ili estas.
Possessive sia agrees with what is possessed, not with the broad or plural-like meaning of oni:
Oni devas konservi siajn kvitancojn dum kvin jaroj.
One must keep one's receipts for five years.
Siajn is plural accusative because kvitancojn is plural and is the object of konservi.
Questions, rules, and instructions
Generic questions naturally use oni when asking what is permitted, customary, or possible for anyone.
Ĉu oni povas aĉeti biletojn ĉe la ŝoforo?
Can you buy tickets from the driver?
— Kiel oni atingas la malnovan urbon de ĉi tie? — Oni prenu la tramon numeron kvar.
— How do you get to the old town from here? — Take tram number four.
The response uses oni + U-form to express general advice: roughly “one should take.” Direct advice to the present listener can instead use a command with understood vi: Prenu la tramon numeron kvar. Both are correct, but their interpersonal framing differs.
Official rules and academic explanations commonly favor oni because it avoids pretending that only the reader is under discussion. This is neutral in every register, including (formal) and (academic) writing.
Do not mix reference systems mid-sentence
Once oni establishes a generic participant, its reflexives should remain third-person. Switching to vi/via without a real change of addressee makes the perspective unstable.
Kiam oni translokiĝas al nova urbo, oni bezonas tempon por trovi sian lokon.
When you move to a new city, you need time to find your place.
If the speaker wants to pivot from general truth to personal advice, signal it clearly:
Kiam oni translokiĝas, la unuaj semajnoj ofte estas malfacilaj. Vi tamen jam konas du homojn tie.
When one moves, the first weeks are often difficult. You, however, already know two people there.
The second sentence now addresses a particular listener, so vi is motivated.
For the broader paradigm, see Oni.
Common Mistakes
1. Copying generic English you as vi
❌ En vintro vi bezonas varmajn vestojn.
Wrong for a general claim: vi addresses the current listener personally.
✅ En vintro oni bezonas varmajn vestojn.
In winter, you need warm clothes.
2. Using onia for the subject's own possession
❌ Oni devas montri onian pasporton.
Incorrect for one's own passport: the possessive refers back to subject oni.
✅ Oni devas montri sian pasporton.
One must show one's passport.
3. Leaving object oni without -n
❌ Tia novaĵo povas surprizi oni.
Incorrect: the generic person is the direct object.
✅ Tia novaĵo povas surprizi onin.
Such news can surprise one.
4. Making predicative agreement plural automatically
❌ Post la kuro oni estas lacaj.
Incorrect in neutral usage: oni normally takes singular predicative agreement.
✅ Post la kuro oni estas laca.
After the run, one is tired.
5. Using si as the generic subject
❌ Si neniam scias, kio okazos.
Incorrect: si cannot be a subject.
✅ Oni neniam scias, kio okazos.
You never know what will happen.
Key Takeaways
Use oni for an unspecified or generic person and vi for the actual addressee or addressees. Regular onin and onia exist, but when the generic subject refers to itself or its own possession, use sin/sia. Treat oni as singular in neutral agreement, and choose between impersonal oni, direct vi, and an imperative according to whether you are stating a general rule or addressing the listener personally.
Related Topics
- Vi for Singular and PluralA1 — Use vi for one or several addressees, clarify number through context and agreement, and form vin and via regularly.
- OniB1 — Use oni for generic or unidentified human agents, with precise contrasts to vi, ili, passives, and reflexive si.
- Accusative Personal PronounsA1 — Add -n to a personal pronoun when it is a direct object, while leaving pronouns after ordinary prepositions unmarked.
- The Reflexive Pronoun SiA1 — Use si and sin when a third-person subject refers back to itself, and distinguish reflexive reference from ordinary third-person pronouns.
- Possessive Forms in -AA1 — Form Esperanto possessives by adding -a to personal pronouns and use them as determiner-like words before nouns.
- Overusing Subject PronounsA2 — Avoid English-style dummy and repeated subjects while retaining the overt subjects that ordinary Esperanto finite clauses require.