Ser is the most irregular verb in Spanish. Its forms come from at least three different Latin verbs that merged over the centuries — esse, sedere (to sit), and a few stray pieces — which is why almost no two tenses share a stem. There is no shortcut: you must learn the paradigms. The good news is that ser is also the most frequent verb in the language, so you will master it through sheer exposure faster than any other irregular.
This page gives the full conjugation across every tense and mood, with the vosotros forms that are mandatory in peninsular Spanish. Sois — the iconic vosotros present — is probably the single most recognizable marker of Spain Spanish to a Latin American ear.
Non-finite forms
| Form | Spanish |
|---|---|
| Infinitive | ser |
| Gerundio | siendo |
| Participio | sido |
The gerund siendo and participle sido are both regular in shape but irregular in stem (you might naively expect sendo or sero). They are used constantly: siendo joven, viajé mucho ("being young, I travelled a lot"), he sido feliz ("I have been happy").
Indicative
Presente
| Person | Form |
|---|---|
| yo | soy |
| tú | eres |
| él / ella / usted | es |
| nosotros / nosotras | somos |
| vosotros / vosotras | sois |
| ellos / ellas / ustedes | son |
¿De dónde sois vosotros? — Somos de Salamanca.
Where are you all from? — We're from Salamanca.
The sois form is unique to Spain (and Equatorial Guinea); Latin America has lost the vosotros entirely and uses son with ustedes instead. If you hear sois anywhere in the world, you are almost certainly hearing Spain Spanish.
Pretérito indefinido
| Person | Form |
|---|---|
| yo | fui |
| tú | fuiste |
| él / ella / usted | fue |
| nosotros | fuimos |
| vosotros | fuisteis |
| ellos / ustedes | fueron |
Critical detail: the preterite of ser is identical to the preterite of ir (to go). Fui means both "I was" and "I went." Context always resolves it.
Ayer fui al cine con mis amigos.
Yesterday I went to the cinema with my friends. (ir)
Fui profesora durante diez años.
I was a teacher for ten years. (ser)
The Spanish Royal Academy reformed the spelling of these forms decades ago to remove the historical accents: it is fui, fue, fuiste, fuimos, fuisteis, fueron — never fuí or fué. Writing fuí is a fossilized error you may still see in older texts but is now considered incorrect.
Imperfecto
| Person | Form |
|---|---|
| yo | era |
| tú | eras |
| él / ella / usted | era |
| nosotros | éramos |
| vosotros | erais |
| ellos / ustedes | eran |
Only three Spanish verbs have an irregular imperfect: ser, ir (iba, ibas…), and ver (veía, veías…). Note the accent on éramos — it is the only form with a written accent.
Cuando éramos pequeños, nuestros abuelos vivían en un pueblo de Soria.
When we were little, our grandparents lived in a village in Soria.
Futuro simple
| Person | Form |
|---|---|
| yo | seré |
| tú | serás |
| él / ella / usted | será |
| nosotros | seremos |
| vosotros | seréis |
| ellos / ustedes | serán |
The future is regular in shape: stem ser- plus the standard future endings.
El próximo verano seremos abuelos por primera vez.
Next summer we'll be grandparents for the first time.
Condicional simple
| Person | Form |
|---|---|
| yo | sería |
| tú | serías |
| él / ella / usted | sería |
| nosotros | seríamos |
| vosotros | seríais |
| ellos / ustedes | serían |
Sería mejor que vinierais más temprano.
It would be better if you (all) came earlier.
Compound tenses (indicative)
All compound tenses combine the auxiliary haber with the participle sido. The participle never changes form.
| Tense | Example (yo) | Example (vosotros) |
|---|---|---|
| Pretérito perfecto | he sido | habéis sido |
| Pluscuamperfecto | había sido | habíais sido |
| Pretérito anterior | hube sido | hubisteis sido |
| Futuro compuesto | habré sido | habréis sido |
| Condicional compuesto | habría sido | habríais sido |
Habéis sido muy generosos con nosotros, de verdad.
You (all) have been really generous with us, truly.
The pretérito anterior (hube sido) is now archaic and appears almost exclusively in formal writing or older literature; in modern Spain Spanish, the pluscuamperfecto (había sido) covers the same ground.
Subjunctive
Presente de subjuntivo
| Person | Form |
|---|---|
| yo | sea |
| tú | seas |
| él / ella / usted | sea |
| nosotros | seamos |
| vosotros | seáis |
| ellos / ustedes | sean |
Note the accent on seáis — required because the stress lands on the e, not the a. Without the accent, seais would be misread as a single syllable.
Quiero que seáis honestos conmigo, aunque me duela.
I want you (all) to be honest with me, even if it hurts.
Imperfecto de subjuntivo
Spanish has two interchangeable forms of the imperfect subjunctive. Both are correct; both are used in Spain, though the -ra form is more frequent in speech and the -se form is slightly more literary.
| Person | -ra form | -se form |
|---|---|---|
| yo | fuera | fuese |
| tú | fueras | fueses |
| él / usted | fuera | fuese |
| nosotros | fuéramos | fuésemos |
| vosotros | fuerais | fueseis |
| ellos / ustedes | fueran | fuesen |
Si fuera más joven, me iría a recorrer el Camino de Santiago.
If I were younger, I'd go and walk the Camino de Santiago.
The accent on fuéramos and fuésemos is mandatory — same logic as éramos.
Compound subjunctive
| Tense | Example (yo) | Example (vosotros) |
|---|---|---|
| Pretérito perfecto de subjuntivo | haya sido | hayáis sido |
| Pluscuamperfecto de subjuntivo | hubiera/hubiese sido | hubierais/hubieseis sido |
Espero que no hayáis sido demasiado duros con él.
I hope you (all) haven't been too hard on him.
Imperative
| Person | Affirmative | Negative |
|---|---|---|
| tú | sé | no seas |
| usted | sea | no sea |
| nosotros | seamos | no seamos |
| vosotros | sed | no seáis |
| ustedes | sean | no sean |
The tú form sé carries a written accent to distinguish it from se (the reflexive pronoun and impersonal se).
Sé tú mismo y todo irá bien.
Be yourself and everything will go well.
The vosotros imperative sed is the form you would actually use in writing or formal speech in Spain, but in casual speech most Spaniards substitute the infinitive: ¡ser buenos! instead of ¡sed buenos!. Both are heard; the infinitive form is technically incorrect but extremely widespread. This is true of all verbs in vosotros imperative, not just ser.
No seáis tan duros con vuestro hermano pequeño.
Don't be so hard on your little brother.
High-frequency phrases with ser
These are collocations and constructions you will hear constantly in Spain. Memorize them as units, not as ser + something.
- ser de
- place → to be from somewhere: Soy de Bilbao.
- ser de
- ser de
- material → to be made of: La mesa es de roble.
- ser para
- recipient → to be for someone: Estas flores son para ti.
- es que… → it's that… (giving an excuse or reason): No puedo ir, es que tengo que trabajar.
- o sea → I mean, that is to say (extremely common in Spain): Llegó tarde, o sea, como siempre.
- a no ser que
- subjunctive → unless: Iremos al parque, a no ser que llueva.
- sea como sea → whatever the case, no matter what: Sea como sea, hay que terminarlo hoy.
O sea, que al final no vienes, ¿no?
So basically, you're not coming in the end, are you?
Sea como sea, tenemos que tomar una decisión esta semana.
One way or another, we have to make a decision this week.
Common Mistakes
❌ Yo fuí al cine ayer.
Incorrect — modern Spanish drops the accent: fui, not fuí.
✅ Yo fui al cine ayer.
I went to the cinema yesterday.
❌ Cuando era pequeño, fuimos a la playa cada verano.
Incorrect — habitual past actions take the imperfect (íbamos), not the preterite. Even though fui/fuimos is a real form, here we need íbamos.
✅ Cuando era pequeño, íbamos a la playa cada verano.
When I was little, we used to go to the beach every summer.
❌ Quiero que tú seas honesto, y que vosotros seais también honestos.
Incorrect — the vosotros present subjunctive requires the accent: seáis, not seais.
✅ Quiero que tú seas honesto, y que vosotros seáis también honestos.
I want you to be honest, and you (all) to be honest too.
❌ Se bueno con tu abuela.
Incorrect — the tú imperative needs a written accent (sé) to distinguish it from the pronoun se.
✅ Sé bueno con tu abuela.
Be good to your grandmother. (tú)
❌ Sé buenos con vuestra abuela.
Incorrect — sé is the tú singular imperative; the plural vosotros form is sed.
✅ Sed buenos con vuestra abuela.
Be good to your grandmother. (vosotros)
❌ Si yo era rico, te compraría una casa.
Incorrect — counterfactual conditionals require the imperfect subjunctive (fuera/fuese), not the imperfect indicative.
✅ Si yo fuera rico, te compraría una casa.
If I were rich, I'd buy you a house.
Key takeaways
- Ser is suppletive: its forms come from multiple historical roots, which is why almost no two tenses share a stem.
- The preterite (fui, fuiste, fue…) is identical to ir's preterite; context disambiguates.
- Only three Spanish verbs have an irregular imperfect: ser, ir, ver.
- Modern Spanish writes fui, fue, fuimos without accents — older texts may show fuí, fué.
- The vosotros forms (sois, fuisteis, erais, seáis, fuerais, sed) are mandatory in peninsular Spanish.
- The tú imperative sé needs the accent to distinguish from the pronoun se.
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Start learning Spanish→Related Topics
- Presente de indicativo: serA1 — The full peninsular conjugation of ser — soy, eres, es, somos, sois, son — with its core uses for identity, origin, profession, time, and material.
- Pretérito de ser y de ir: fui, fuiste, fueA2 — Ser and ir share an identical preterite conjugation — fui, fuiste, fue, fuimos, fuisteis, fueron — and context alone tells them apart. No accents, despite a common native temptation to add one.
- Imperfecto de ser: era, eras, eraA2 — The imperfect of ser — era, eras, era, éramos, erais, eran — one of only three irregular imperfects in Spanish, with the accent only on éramos, and the workhorse forms used for past identity, age, time, and description.
- 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.