The Spanish subjunctive's most famous job is to mark doubt. Whenever a matrix clause questions, doubts, denies or simply fails to assert the truth of an embedded clause, that embedded clause takes the subjunctive. This category contains the trigger pattern that English speakers find most counter-intuitive — the affirmative/negative flip with creer que and pensar que — which is why this page treats it as the central case rather than a footnote.
The principle
A que-clause is in the indicative when the matrix verb asserts it as true: Sé que viene, Creo que viene, Es verdad que viene. The same clause goes to the subjunctive when the matrix verb questions, doubts or denies that truth: Dudo que venga, No creo que venga, No es verdad que venga.
This is the cleanest illustration of what the subjunctive does: it marks the embedded clause as not asserted by the matrix. With doubt verbs, the matrix actively says "I'm not claiming this is true" — and the subjunctive follows automatically.
The main triggers
| Trigger | Translation | Example |
|---|---|---|
| dudar que | to doubt that | Dudo que llegue a tiempo. |
| no creer que | not to think / believe that | No creo que sea verdad. |
| no pensar que | not to think that | No pienso que tenga razón. |
| no estar seguro de que | not to be sure that | No estoy seguro de que venga. |
| negar que | to deny that | Niegan que haya pasado. |
| no es verdad que | it's not true that | No es verdad que esté enfermo. |
| no es cierto que | it's not the case that | No es cierto que sepa la respuesta. |
| es posible que | it's possible that | Es posible que llueva. |
| es probable que | it's likely that | Es probable que llueva. |
| puede que | (it) may be that | Puede que tenga razón. |
| es dudoso que | it's doubtful that | Es dudoso que apruebe. |
Dudo mucho que mi hermano sepa cocinar algo más que pasta.
I really doubt my brother knows how to cook anything other than pasta.
No estoy seguro de que el banco abra mañana — es festivo.
I'm not sure the bank is open tomorrow — it's a holiday.
Es probable que nos llamen esta tarde con los resultados.
It's likely they'll call us this afternoon with the results.
The affirmative/negative flip: creer, pensar, estar seguro
This is the rule that catches every English-speaking learner. Three verbs — creer, pensar, estar seguro de — switch mood depending on whether the matrix is affirmative or negative.
| Affirmative → indicative | Negative → subjunctive |
|---|---|
| Creo que viene mañana. | No creo que venga mañana. |
| Pienso que tiene razón. | No pienso que tenga razón. |
| Estoy seguro de que viene. | No estoy seguro de que venga. |
| Me parece que es verdad. | No me parece que sea verdad. |
The logic is exactly the same as everywhere else in the subjunctive system. Creo que viene asserts a belief that he comes — the matrix is doing assertion work, so the embedded clause is indicative. No creo que venga denies that belief — the matrix is no longer asserting that he comes, so the embedded clause goes subjunctive.
Creo que tiene razón, aunque a veces se pasa de listo.
I think he's right, even if he sometimes acts too clever.
No creo que tenga razón en esto — los datos dicen lo contrario.
I don't think he's right about this — the data say otherwise.
The same flip works with questions, because a question doesn't assert either:
¿Crees que venga a la fiesta?
Do you think she'll come to the party?
Note the subjunctive venga — the speaker is asking, not asserting, so the mood follows the doubt pattern. The indicative ¿Crees que viene? is also possible, and slightly more neutral; the subjunctive version conveys that the speaker has real doubts about whether she'll come.
Es posible, es probable, puede que
These three expressions are pure doubt-triggers — they take the subjunctive regardless of any further negation, because their lexical meaning already places the embedded clause in the realm of possibility rather than fact.
Puede que esté de viaje y por eso no contesta.
It may be that she's away travelling and that's why she's not answering.
Es posible que mañana haga mucho calor.
It's possible it'll be very hot tomorrow.
Es probable que recibamos una respuesta antes del viernes.
It's likely we'll get an answer before Friday.
A subtle point: seguramente and probablemente used as standalone adverbs often take the indicative (Probablemente viene mañana) or the subjunctive (Probablemente venga mañana) depending on the speaker's degree of confidence. The subjunctive version is more cautious; the indicative version is more confident. Both are grammatical.
Quizá and tal vez
Quizá (and its variant quizás) and tal vez both mean "perhaps." Both are typically followed by the subjunctive when the speaker is genuinely uncertain, and the indicative when the speaker is leaning toward asserting the embedded clause.
| Subjunctive (uncertain) | Indicative (more confident) |
|---|---|
| Quizá venga mañana. | Quizá viene mañana. |
| Tal vez tengas razón. | Tal vez tienes razón. |
In peninsular Spanish, the subjunctive is the default with quizá and tal vez in cautious or formal speech. The indicative is also common in everyday spoken usage, especially when the speaker is mostly persuaded. Either way, this is one of the few places in the modern language where the speaker truly has a stylistic choice.
Quizá no tenga ganas de salir esta noche, ya veremos.
Maybe I won't feel like going out tonight, we'll see.
Tal vez sea mejor que se lo digamos en persona.
Perhaps it's better that we tell him in person.
A note on word order: quizá and tal vez trigger the subjunctive only when they precede the verb. After the verb, they have no syntactic force: Viene quizá mañana takes indicative because quizá has become a parenthetical adverb. The subjunctive lives in the construction quizá + verb, not in the word quizá itself.
A subtler case: negar and not-negar
Negar que ("to deny that") takes subjunctive in its affirmative form because the matrix verb already does denial work: Niega que sea posible — "he denies that it's possible." When negated (no negar que), it flips to indicative, because the double negative restores assertion: No niega que sea / es posible. Both moods are heard; the indicative is more common when the speaker treats the embedded clause as a fact the subject has been forced to admit.
El acusado niega que conozca al testigo.
The defendant denies that he knows the witness.
No niego que tenga sus virtudes, pero a mí no me convence.
I don't deny that he has his merits, but he doesn't convince me.
Comparison with English
English signals doubt mainly through word choice (I doubt, I'm not sure, maybe) and leaves the embedded verb in the indicative or in some neutral form. There is no English mood that systematically marks "the matrix isn't asserting this."
The trickiest gap for English speakers is the no creo que + subjunctive pattern. English would say I don't think it's true with no change to "is true." Spanish requires the flip: No creo que sea verdad. Learners reach for No creo que es verdad, which is the single most common B1 error in this category.
A second gap: quizá and tal vez don't have an English equivalent that systematically takes the subjunctive. English uses perhaps + indicative across the board. The Spanish mood distinction expresses a nuance that English speakers usually convey through tone of voice or hedging adverbs.
Common Mistakes
❌ No creo que tiene razón.
Incorrect — no creer que takes subjunctive (tenga), even though affirmative creer que takes indicative.
✅ No creo que tenga razón.
I don't think he's right.
❌ Dudo que viene a la reunión.
Incorrect — dudar que always takes subjunctive (venga).
✅ Dudo que venga a la reunión.
I doubt he'll come to the meeting.
❌ Es posible que llueve mañana.
Incorrect — es posible que always takes subjunctive (llueva).
✅ Es posible que llueva mañana.
It's possible it'll rain tomorrow.
❌ Quizá tienes razón, no lo sé.
In Peninsular Spanish, the cautious version uses subjunctive after quizá (tengas).
✅ Quizá tengas razón, no lo sé.
Maybe you're right, I don't know.
❌ No estoy seguro que esté bien.
Incorrect — no estar seguro takes the preposition de before que.
✅ No estoy seguro de que esté bien.
I'm not sure he's okay.
Key Takeaways
- Doubt-triggers always take subjunctive: dudar que, negar que, no es verdad que, no es cierto que, es posible/probable/dudoso que, puede que.
- The affirmative/negative flip: creer que / pensar que / estar seguro de que take indicative when affirmative and subjunctive when negated.
- The flip extends to questions: ¿Crees que venga? (subjunctive expresses real doubt) vs ¿Crees que viene? (indicative is more neutral).
- Quizá / quizás / tal vez take subjunctive when they precede the verb and the speaker is uncertain; indicative when the speaker is more confident or when the adverb is post-verbal.
- The underlying logic is the same as in every other subjunctive trigger: the matrix clause isn't asserting the embedded clause, so the embedded clause goes subjunctive.
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