Pensar is the verb for to think in every sense English uses that word for — to hold an opinion, to consider, to reflect, to plan. It is the textbook e→ie stem-changing -ar verb: when the stem vowel e is stressed in the present (yo pienso, tú piensas, él piensa, ellos piensan), it diphthongizes to ie. The shift is absent in nosotros pensamos and vosotros pensáis (where the stress falls on the ending) and absent everywhere outside the present indicative and present subjunctive. Crucially, the preterite is fully regular — pensé, pensaste, pensó — with no stem change at all, a feature -ar (and -er) stem-changers share but -ir stem-changers do not.
The morphology is therefore predictable. The real subtlety of pensar lies in its prepositions: pensar en X (to think about X), pensar de X (to think of X — that is, to have an opinion about X), pensar + infinitive (to plan to do X), and pensar que + indicative (to think that...) which flips to the subjunctive after negation. Getting these prepositions wrong is the single most common error English speakers make with pensar — and the distinctions are sharp enough that the wrong preposition sometimes produces nonsense.
Non-finite forms
| Form | Spanish | English |
|---|---|---|
| Infinitivo | pensar | to think, to consider, to plan |
| Infinitivo compuesto | haber pensado | to have thought |
| Gerundio | pensando | thinking |
| Gerundio compuesto | habiendo pensado | having thought |
| Participio | pensado | thought; (as adj.) considered, planned |
All non-finite forms are fully regular. The gerund stays pensando with no ie — the stress falls on -an-, not on the stem e, so no diphthongization occurs. The participle pensado doubles as the everyday adjective for thought-out / planned: bien pensado (well-considered, smart move), poco pensado (rushed, not well thought out).
Indicative — simple tenses
Presente
| yo | tú | él/ella/usted | nosotros | vosotros | ellos/ellas/ustedes |
|---|---|---|---|---|---|
| pienso | piensas | piensa | pensamos | pensáis | piensan |
The classic "shoe" pattern: every form except nosotros/vosotros takes ie. Stress in pensamos and pensáis falls on the endings, so the stem e stays put. Yo pienso que... is among the top fifty most-uttered sentence openings in spoken Spanish.
Pienso que deberíamos volver antes de que se haga de noche.
I think we should head back before it gets dark.
¿En qué piensas? Llevas un rato mirando por la ventana.
What are you thinking about? You've been staring out the window for a while.
Mis padres piensan que estoy loca por dejar el trabajo.
My parents think I'm crazy for quitting my job.
Pretérito perfecto simple
| yo | tú | él | nosotros | vosotros | ellos |
|---|---|---|---|---|---|
| pensé | pensaste | pensó | pensamos | pensasteis | pensaron |
Fully regular — no stem change in the preterite. This is the headline difference between -ar/-er stem-changers (like pensar and entender) and -ir stem-changers (like pedir and sentir). The former lose their stem change in the preterite entirely; the latter keep it in the third person. So pensar gives pensó (regular), while sentir gives sintió (stem change preserved).
Pensé que me ibas a llamar y me quedé en casa esperando.
I thought you were going to call me and I stayed home waiting.
Cuando vio el precio, lo pensó dos veces antes de aceptar.
When he saw the price, he thought twice before accepting.
Pretérito imperfecto
| yo | tú | él | nosotros | vosotros | ellos |
|---|---|---|---|---|---|
| pensaba | pensabas | pensaba | pensábamos | pensabais | pensaban |
Fully regular. Pensaba que... (I thought that, I used to think that) is one of the most common ways to set up a contrast with reality: pensaba que era más alto (I thought he was taller).
Pensaba que el examen iba a ser más fácil, qué inocente fui.
I thought the exam was going to be easier, how naive I was.
Futuro simple
| yo | tú | él | nosotros | vosotros | ellos |
|---|---|---|---|---|---|
| pensaré | pensarás | pensará | pensaremos | pensaréis | pensarán |
Lo pensaré con calma y te digo algo mañana.
I'll think it over carefully and let you know tomorrow.
Condicional
| yo | tú | él | nosotros | vosotros | ellos |
|---|---|---|---|---|---|
| pensaría | pensarías | pensaría | pensaríamos | pensaríais | pensarían |
Yo nunca pensaría algo así de ti, no me lo creo.
I'd never think something like that about you, I don't believe it.
Indicative — compound tenses
Pretérito perfecto compuesto
| yo | tú | él | nosotros | vosotros | ellos |
|---|---|---|---|---|---|
| he pensado | has pensado | ha pensado | hemos pensado | habéis pensado | han pensado |
He pensado que... (I was thinking that..., I've been thinking that...) is the standard peninsular opener for proposing an idea that you've been mulling over.
He pensado que igual nos vamos a la sierra este finde, ¿qué te parece?
I was thinking we might head up to the mountains this weekend, what do you think?
Pretérito pluscuamperfecto
| yo | tú | él | nosotros | vosotros | ellos |
|---|---|---|---|---|---|
| había pensado | habías pensado | había pensado | habíamos pensado | habíais pensado | habían pensado |
Yo había pensado en regalarle un libro, pero al final le compré una planta.
I'd been thinking of giving him a book, but in the end I bought him a plant.
Futuro compuesto
| yo | tú | él | nosotros | vosotros | ellos |
|---|---|---|---|---|---|
| habré pensado | habrás pensado | habrá pensado | habremos pensado | habréis pensado | habrán pensado |
Condicional compuesto
| yo | tú | él | nosotros | vosotros | ellos |
|---|---|---|---|---|---|
| habría pensado | habrías pensado | habría pensado | habríamos pensado | habríais pensado | habrían pensado |
Nunca habría pensado que acabaríamos siendo amigos después de aquella discusión.
I would never have thought we'd end up being friends after that argument.
Subjunctive — simple tenses
Presente de subjuntivo
| yo | tú | él | nosotros | vosotros | ellos |
|---|---|---|---|---|---|
| piense | pienses | piense | pensemos | penséis | piensen |
Same boot pattern as the indicative: ie in every form except nosotros pensemos / vosotros penséis. This is unlike -ir stem-changers, where the change propagates everywhere. The polarity rule applies here: creo que / pienso que + indicative, but no creo que / no pienso que + subjunctive.
No pienses que me he olvidado de ti, solo he estado liadísima.
Don't think I've forgotten about you, I've just been swamped.
Es importante que pensemos bien antes de tomar una decisión.
It's important that we think it through before making a decision.
Imperfecto de subjuntivo (-ra / -se)
| yo | tú | él | nosotros | vosotros | ellos | |
|---|---|---|---|---|---|---|
| -ra | pensara | pensaras | pensara | pensáramos | pensarais | pensaran |
| -se | pensase | pensases | pensase | pensásemos | pensaseis | pensasen |
No stem change in the imperfect subjunctive — it's built off the third-person preterite stem (pensaron → pensara-), and since the preterite is regular, the imperfect subjunctive is too.
Me pidió que pensara en él antes de decidir nada.
He asked me to think of him before deciding anything.
Subjunctive — compound tenses
Pretérito perfecto de subjuntivo
| yo | tú | él | nosotros | vosotros | ellos |
|---|---|---|---|---|---|
| haya pensado | hayas pensado | haya pensado | hayamos pensado | hayáis pensado | hayan pensado |
No me extraña que hayan pensado en vender la casa, está enorme para ellos dos.
I'm not surprised they've been thinking about selling the house, it's huge for just the two of them.
Pluscuamperfecto de subjuntivo
| yo | tú | él | nosotros | vosotros | ellos | |
|---|---|---|---|---|---|---|
| -ra | hubiera pensado | hubieras pensado | hubiera pensado | hubiéramos pensado | hubierais pensado | hubieran pensado |
| -se | hubiese pensado | hubieses pensado | hubiese pensado | hubiésemos pensado | hubieseis pensado | hubiesen pensado |
Imperative
| Form | Affirmative | Negative |
|---|---|---|
| tú | piensa | no pienses |
| usted | piense | no piense |
| nosotros | pensemos | no pensemos |
| vosotros | pensad | no penséis |
| ustedes | piensen | no piensen |
The diphthong shows up wherever the stem is stressed and disappears in nosotros/vosotros — same boot pattern as the indicative and subjunctive. Piénsalo (think about it) is one of the most-uttered single-word commands in conversational Spain Spanish, used to push someone to reconsider.
Piénsalo bien antes de aceptar, no hay vuelta atrás.
Think it over carefully before accepting, there's no going back.
No penséis tanto y disfrutad del momento.
Don't overthink it and enjoy the moment.
Pensar en vs pensar de vs pensar que vs pensar + infinitive
This is the heart of using pensar well. The four constructions are not interchangeable, and the wrong choice produces sentences a native speaker would never say.
pensar en X — to think about X (have X on your mind)
The most common use. En introduces the topic or person occupying your mental space — what you are thinking about.
No puedo dejar de pensar en lo que me dijiste ayer.
I can't stop thinking about what you told me yesterday.
¿En qué piensas tanto últimamente? Pareces lejos.
What are you thinking about so much lately? You seem far away.
pensar de X — what do you think of X (opinion)
Pensar de asks for an evaluation, an opinion of something. Almost always appears in the question form ¿qué piensas / opinas de...? In affirmative answers, native speakers tend to switch to creo / opino / me parece, but the de construction is still standard for the question.
¿Qué piensas de la nueva ley de vivienda? A mí me parece un parche.
What do you think of the new housing law? It seems like a patch job to me.
¿Qué piensas de él? — Sinceramente, no me fío.
What do you think of him? — Honestly, I don't trust him.
The mistake is to use en here: ¿qué piensas en él? is not idiomatic Spanish for what do you think of him?. It would suggest you're thinking about him as a subject of contemplation, not evaluating him.
pensar que + indicative — to think / believe that...
The verb of opinion, equivalent to creer que in many contexts. The clause takes the indicative when affirmative, but flips to the subjunctive under negation (no pienso que / no creo que).
Pienso que tienes razón, aunque no me guste admitirlo.
I think you're right, even though I don't like admitting it.
No pienso que sea tan grave como dicen los medios.
I don't think it's as serious as the media are making out.
pensar + infinitive — to plan / intend to
Without any preposition, pensar followed directly by an infinitive means to plan, to intend. This is the construction English speakers most often miss — they reach for planear (which works but sounds bookish) instead of the natural pensar + infinitive.
¿Qué piensas hacer este verano? ¿Te vas fuera?
What are you planning to do this summer? Are you going away?
Pienso terminar el máster en junio y luego buscar trabajo.
I plan to finish the master's in June and then look for work.
High-frequency expressions with pensar
| Phrase | Meaning |
|---|---|
| pensar en voz alta | to think out loud |
| pensarlo dos veces | to think twice |
| dar que pensar | to make one think (give pause) |
| sin pensarlo | without thinking, on the spot |
| pensándolo bien | now that I think about it |
| cuando menos te lo piensas | when you least expect it |
| no pensaba en eso | I wasn't thinking of that / I hadn't considered that |
| ¡ni lo pienses! | don't even think about it! |
¡Ni lo pienses! is the classic peninsular shutdown — used to head off a suggestion you find absurd or unacceptable.
¿Coger el coche con esta nevada? ¡Ni lo pienses!
Take the car in this snowstorm? Don't even think about it!
Pensándolo bien, igual sí que tienes razón.
Now that I think about it, maybe you are right after all.
Common Mistakes
❌ Yo penso que tienes razón.
The yo form takes the e→ie shift: pienso, not penso.
✅ Yo pienso que tienes razón.
I think you're right.
❌ Estoy piensando en ti todo el día.
The gerund is pensando, with no diphthong — the stress falls on -an-, not on the stem e. Stem change does not apply in the gerund of -ar verbs.
✅ Estoy pensando en ti todo el día.
I'm thinking about you all day.
❌ ¿Qué piensas en la nueva profesora?
To ask for an opinion, use pensar de, not pensar en. Pensar en means to have someone on one's mind, not to evaluate them.
✅ ¿Qué piensas de la nueva profesora?
What do you think of the new teacher?
❌ Pienso a viajar a Japón el año que viene.
To plan to do something, pensar takes the infinitive directly, with no preposition.
✅ Pienso viajar a Japón el año que viene.
I'm planning to travel to Japan next year.
❌ No pienso que es una buena idea.
After no pienso que, Spanish requires the subjunctive: sea, not es.
✅ No pienso que sea una buena idea.
I don't think it's a good idea.
Key Takeaways
- Pensar is an e→ie stem-changing -ar verb. The diphthong appears whenever the stem vowel is stressed — that is, in all forms of the present indicative and subjunctive except nosotros/vosotros.
- The preterite is fully regular (pensé, pensaste, pensó) — a key contrast with -ir stem-changers, which keep the shift in third-person preterite. Likewise no stem change in the imperfect, future, conditional, gerund (pensando), or imperfect subjunctive.
- Four constructions, four meanings: pensar en (think about), pensar de (have an opinion of), pensar que + indicative (believe that), pensar + infinitive (plan to). The last one needs no preposition.
- After negative no pienso que / no creo que, Spanish switches to the subjunctive — no pienso que sea verdad.
- Piénsalo (think it over) and ¡ni lo pienses! (don't even think about it) are two of the most-uttered imperative forms of pensar in spoken Spain.
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- Cambio vocálico: e>ie (pensar, querer, preferir)A2 — The most common stem-change pattern in Spanish: stressed e becomes ie in the 'boot' forms — yo, tú, él, ellos — while nosotros and vosotros keep the simple e.
- Pretérito indefinido: verbos regulares en -arA2 — The regular -ar preterite — endings -é, -aste, -ó, -amos, -asteis, -aron — with obligatory accents, the peninsular vosotros form, and the today/not-today rule that governs when to use it in Spain.
- Verbos seguidos de 'en' + infinitivoB2 — A small but high-frequency set of verbs takes 'en' before an infinitive — insistir en, pensar en, tardar en, consistir en — clustered around focus, duration, and absorbing one's attention into an action.
- Subjuntivo vs indicativo: cuando importa la elecciónB1 — Several Spanish constructions accept either mood — and the choice changes the meaning. Here's how to choose.
- saberA1 — Full conjugation reference for saber (to know — facts, information, how to do something) — a profoundly irregular high-frequency verb with the unique yo form sé, a u-stem preterite (supe, supiste, supo) with the meaning shift 'found out', a dropped-vowel future (sabré), and the suppletive subjunctive sepa. Covers every tense, the saber vs conocer split, and the idiomatic uses peninsular speakers use daily.