Ser is one of the two Spanish verbs translated as English "to be" — the other being estar — and it is, by every measure, one of the most irregular verbs in the language. Almost no tense of ser uses the infinitive's stem. The present indicative soy, eres, es, somos, sois, son is suppletive (built from a different Latin root than the infinitive). The preterite fui, fuiste, fue, fuimos, fuisteis, fueron is shared, form-for-form, with ir ("to go") — context, and only context, tells you which verb you're looking at. The imperfect era, eras, era, éramos, erais, eran is one of only three irregular imperfects in all of Spanish (along with ir and ver). The present subjunctive sea, seas, sea, seamos, seáis, sean comes from yet another stem. The tú affirmative imperative is the single-syllable sé — written with an accent, identical in form to the yo present of saber.
This page lays out every paradigm of ser in full. The companion page on ser vs estar covers when to use ser rather than estar; this reference focuses on the forms themselves, with usage notes that touch on the high-frequency contexts where peninsular speakers use ser every day.
Non-finite forms
| Form | Spanish | English |
|---|---|---|
| Infinitivo | ser | to be |
| Infinitivo compuesto | haber sido | to have been |
| Gerundio | siendo | being |
| Gerundio compuesto | habiendo sido | having been |
| Participio | sido | been |
The participle sido is invariable in compound tenses (he sido, has sido, ha sido) — it does not agree with the subject in number or gender. The gerund siendo is widely used in concessive constructions like siendo así, … ("that being so, …") and aun siendo ("even being").
Indicative — simple tenses
Presente
| yo | tú | él/ella/usted | nosotros | vosotros | ellos/ellas/ustedes |
|---|---|---|---|---|---|
| soy | eres | es | somos | sois | son |
All six forms are irregular. None follow any predictable pattern from the infinitive. The vosotros form sois is the diagnostic mark of peninsular Spanish (Latin American varieties use son with ustedes in place of sois). It's a short, sharp form — one syllable — and it appears in every casual conversation: ¿Sois de aquí? ¿De dónde sois?
The most distinctive feature of soy/voy/doy/estoy is the final -y. Spanish has only five verbs with this -y in the yo present: soy, voy, doy, estoy, hay (the impersonal form of haber). It's a small enough set to memorize as a unit.
Yo soy de un pueblo pequeño de la sierra, mis padres todavía viven allí.
I'm from a small village in the mountains — my parents still live there.
¿Vosotros sois los nuevos del cuarto B?
Are you the new ones from flat 4B?
No es justo lo que han hecho con vosotros.
What they've done to you is not fair.
Pretérito perfecto simple
| yo | tú | él | nosotros | vosotros | ellos |
|---|---|---|---|---|---|
| fui | fuiste | fue | fuimos | fuisteis | fueron |
The preterite of ser is identical to the preterite of ir. Fui médico = "I was a doctor"; Fui al médico = "I went to the doctor." No spelling distinction exists. Note also that neither fui nor fue carries a written accent — these forms used to take one until 1959, when the Real Academia removed it (monosyllables without ambiguity lose their accent). Many learners — and many older books — still mark them; modern style does not.
El verano pasado fui monitor de un campamento en Asturias.
Last summer I was a counsellor at a camp in Asturias.
No fue culpa tuya, no le des más vueltas.
It wasn't your fault — stop dwelling on it.
Pretérito imperfecto
| yo | tú | él | nosotros | vosotros | ellos |
|---|---|---|---|---|---|
| era | eras | era | éramos | erais | eran |
One of only three irregular imperfects in Spanish (ser → era, ir → iba, ver → veía). The accent on éramos is mandatory — the stress falls on the antepenultimate syllable, which always takes a graphic accent.
Era is the unmarked tense for description, identity, and background in the past — what someone was like, what their job was, what time it was, what the weather looked like. Pairing it correctly with fue (preterite) is one of the central skills of intermediate Spanish: Cuando era niño, fui una vez a París — "When I was a child, I went to Paris once."
De joven mi abuela era profesora en un colegio del pueblo.
In her youth my grandmother was a teacher at a village school.
Eran las cuatro de la madrugada cuando sonó el timbre.
It was four in the morning when the doorbell rang.
Futuro simple
| yo | tú | él | nosotros | vosotros | ellos |
|---|---|---|---|---|---|
| seré | serás | será | seremos | seréis | serán |
The future is built on the regular stem ser- — one of the few zones of ser that's perfectly predictable. Endings are universal -é, -ás, -á, -emos, -éis, -án.
The future of ser is also one of the standard ways to express conjecture about the present in Spanish: Será de Sevilla — "He must be from Seville." This use is constant in everyday speech, not literary or formal.
No sé quién llama a estas horas, será mi hermana otra vez.
I don't know who's calling at this hour — must be my sister again.
Cuando crezcas serás médico como tu padre, ya verás.
When you grow up you'll be a doctor like your father, you'll see.
Condicional
| yo | tú | él | nosotros | vosotros | ellos |
|---|---|---|---|---|---|
| sería | serías | sería | seríamos | seríais | serían |
Same regular ser- stem as the future. The conditional of ser is the workhorse of polite suggestions and hypothetical claims: Sería mejor que… ("It would be better if…"), Yo no sería capaz ("I wouldn't be able to").
Sería una pena que no vinieras a la fiesta.
It'd be a shame if you didn't come to the party.
Indicative — compound tenses
All compound tenses use haber + sido. The participle never agrees with anything.
Pretérito perfecto compuesto
| yo | tú | él | nosotros | vosotros | ellos |
|---|---|---|---|---|---|
| he sido | has sido | ha sido | hemos sido | habéis sido | han sido |
Esto ha sido un desastre de principio a fin.
This has been a disaster from start to finish.
Pretérito pluscuamperfecto
| yo | tú | él | nosotros | vosotros | ellos |
|---|---|---|---|---|---|
| había sido | habías sido | había sido | habíamos sido | habíais sido | habían sido |
Hasta entonces nunca había sido tan feliz en mi vida.
Until then I'd never been so happy in my life.
Futuro compuesto
| yo | tú | él | nosotros | vosotros | ellos |
|---|---|---|---|---|---|
| habré sido | habrás sido | habrá sido | habremos sido | habréis sido | habrán sido |
Condicional compuesto
| yo | tú | él | nosotros | vosotros | ellos |
|---|---|---|---|---|---|
| habría sido | habrías sido | habría sido | habríamos sido | habríais sido | habrían sido |
Sin tu ayuda esto habría sido imposible.
Without your help this would have been impossible.
Subjunctive — simple tenses
Presente de subjuntivo
| yo | tú | él | nosotros | vosotros | ellos |
|---|---|---|---|---|---|
| sea | seas | sea | seamos | seáis | sean |
The present subjunctive is built on the suppletive stem se-. Sea belongs to the small group of fully irregular Spanish present subjunctives (sea, esté, dé, haya, vaya, sepa) — none of these can be derived from the yo present indicative the way most subjunctives can.
The phrase o sea ("that is, I mean") — literally "or [it] be" — is one of the most-used discourse markers in spoken peninsular Spanish, used to reformulate, hedge, or clarify. Many speakers use it as a sentence filler. It's not literary; it's everyday speech.
Quiero que mi hijo sea feliz, lo demás me da igual.
I want my son to be happy — everything else is irrelevant to me.
No es que sea tonto, o sea, es que no se entera.
It's not that he's stupid — I mean, he just doesn't get it.
Imperfecto de subjuntivo (-ra / -se)
| yo | tú | él | nosotros | vosotros | ellos | |
|---|---|---|---|---|---|---|
| -ra | fuera | fueras | fuera | fuéramos | fuerais | fueran |
| -se | fuese | fueses | fuese | fuésemos | fueseis | fuesen |
Built on the preterite fueron — and again, identical to the imperfect subjunctive of ir. Both verbs share both stems, in both moods, in the past. The -ra forms are the spoken default in Spain; -se survives in writing and formal speech.
Si yo fuera tú, no diría nada hasta mañana.
If I were you, I wouldn't say anything until tomorrow.
Subjunctive — compound tenses
Pretérito perfecto de subjuntivo
| yo | tú | él | nosotros | vosotros | ellos |
|---|---|---|---|---|---|
| haya sido | hayas sido | haya sido | hayamos sido | hayáis sido | hayan sido |
Me alegro de que haya sido tan fácil organizarlo.
I'm glad it's been so easy to organize.
Pluscuamperfecto de subjuntivo
| yo | tú | él | nosotros | vosotros | ellos | |
|---|---|---|---|---|---|---|
| -ra | hubiera sido | hubieras sido | hubiera sido | hubiéramos sido | hubierais sido | hubieran sido |
| -se | hubiese sido | hubieses sido | hubiese sido | hubiésemos sido | hubieseis sido | hubiesen sido |
Imperative
| Form | Affirmative | Negative |
|---|---|---|
| tú | sé | no seas |
| usted | sea | no sea |
| nosotros | seamos | no seamos |
| vosotros | sed | no seáis |
| ustedes | sean | no sean |
The tú affirmative sé is the most distinctive form here — short, irregular, and identical in spelling to the yo present indicative of saber. The written accent is obligatory: it distinguishes the imperative from the pronoun se. Sé bueno ("be good"), sé valiente ("be brave"), sé tú mismo ("be yourself") — all everyday uses.
The negative no seas is the spoken-Spanish refrain for telling someone off: no seas tonto, no seas pesado, no seas así. The vosotros affirmative sed is recognizable but lightly used; speakers often replace it with a softened indicative or subjunctive (haced el favor de ser…).
Sé bueno con tu hermana, que es más pequeña.
Be good to your sister — she's younger.
No seáis tan duros con él, lo está pasando mal.
Don't be so hard on him — he's going through a tough time.
What ser is used for — the core split with estar
This page won't replace the full ser vs estar reference, but the basic split is worth fixing here:
- Identity & definition — who or what something is: Es médico. Es mi hermana. Es un coche.
- Origin & nationality — where someone is from: Soy de Cádiz. Es portugués.
- Material & possession — what something is made of / belongs to: Es de madera. Es de mi padre.
- Time, date, season — Son las tres. Es lunes. Es verano.
- Permanent/intrinsic qualities — Es alto. Es generoso.
- Passive voice with agent — Fue construido por los romanos.
- Impersonal value judgments — Es importante. Es una pena. Es necesario.
Estar, by contrast, covers location, ongoing states, results, and the progressive. The two are not interchangeable, even though English collapses them into a single "to be."
Mi vecino es de Cádiz pero lleva treinta años en Madrid.
My neighbour is from Cádiz but he's been in Madrid for thirty years.
Es una pena que no podáis venir a la boda.
It's a shame you all can't come to the wedding.
High-frequency collocations from peninsular Spanish
| Phrase | Translation |
|---|---|
| o sea | that is, I mean, in other words |
| es que… | the thing is… (introducing an excuse or explanation) |
| como sea | however / whatever way |
| sea como sea | be that as it may, one way or another |
| a no ser que | unless |
| de ser así | if that's the case (formal) |
| érase una vez | once upon a time (set fairy-tale opener) |
| así es la vida | that's life |
| ¿qué será será? | (informal) what will be will be |
Es que… is the single most-used conversational filler in Spain when someone needs to soften a refusal or explain themselves: Es que no tengo tiempo, es que estoy hasta arriba, es que ya quedé con otra gente. It's a hedge — and Spanish speakers reach for it constantly.
Es que no puedo ir el sábado, lo siento muchísimo.
The thing is, I can't go on Saturday — I'm really sorry.
Sea como sea, mañana hay que entregar el proyecto.
One way or another, the project has to be turned in tomorrow.
Common Mistakes
❌ Yo soy aquí en Madrid.
For location use estar, not ser. Yo estoy aquí en Madrid. (Ser would be used for origin: 'Soy de Madrid.')
✅ Yo estoy aquí en Madrid.
I'm here in Madrid.
❌ Estoy ingeniero.
For profession and identity use ser, not estar. Soy ingeniero.
✅ Soy ingeniero.
I'm an engineer.
❌ Vosotros son de Barcelona.
With vosotros the verb is sois, not son. Son is for ustedes / ellos.
✅ Vosotros sois de Barcelona.
You all are from Barcelona.
❌ Cuando era niño, era una vez a la playa.
For a one-time completed event in the past, Spanish uses the preterite, not the imperfect. The preterite of ser is fui — and it also happens to be the preterite of ir, which is what's meant here: 'I went once.'
✅ Cuando era niño, fui una vez a la playa.
When I was a child, I went to the beach once.
❌ Se bueno con tu hermano.
The tú affirmative imperative of ser is sé (with a written accent), to distinguish it from the reflexive pronoun se.
✅ Sé bueno con tu hermano.
Be good to your brother.
Key Takeaways
- Ser is fully irregular: the present soy, eres, es, somos, sois, son is suppletive; the imperfect era is one of only three irregular imperfects in Spanish; the preterite fui is shared form-for-form with ir; the subjunctive sea comes from a separate stem.
- The peninsular vosotros form sois is unique to Spain — in Latin America ustedes son covers the same plural-you function.
- The preterite forms of ser and ir are identical; only context tells you which verb is meant.
- The future and conditional (seré, sería) are built on the regular stem ser- and are the only fully predictable zones of the paradigm.
- The tú affirmative imperative is the short, accented sé — distinct in writing from the pronoun se.
- Ser covers identity, origin, definition, material, time, and intrinsic qualities. Estar covers location, states, and the progressive. The split is one of the central skills of Spanish.
- O sea (subjunctive of ser) is one of the most-used discourse markers in spoken peninsular Spanish.
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Start learning Spanish→Related Topics
- Conjugación completa de serA1 — Complete conjugation reference for the verb ser across all tenses and moods, with peninsular vosotros forms.
- Usos de serA2 — A complete catalogue of when to use ser — identity, profession, origin, time, material, possession, event location, and the passive voice.
- Ser vs estar: visión generalA1 — The foundational distinction between Spanish's two 'to be' verbs — what each one is for and how to choose.
- Ser vs estar con adjetivosB1 — The adjectives that flip meaning between ser and estar — aburrido, listo, rico, vivo, bueno — and the trait-vs-state logic that makes the contrast predictable.
- estarA1 — Full conjugation reference for estar (to be — location, state, progressive) — fully irregular. Yo-form estoy, accents throughout the present (estás, está, estáis, están), u-stem preterite (estuve), and accented subjunctive (esté). A cardinal verb of peninsular Spanish.
- Subjuntivo presente de ser: seaB1 — The present subjunctive of ser — sea, seas, sea, seamos, seáis, sean — with peninsular vosotros forms, fixed expressions, and the spelling trap of seáis.