Expressing probability and doubt

Expressing probability and doubt in Spanish: overview

In Spanish, whether you use the indicative or the subjunctive often signals how certain you are. Use the indicative for statements you treat as facts or strong beliefs; use the subjunctive after verbs and expressions that show doubt, denial, possibility, or uncertainty.

Two short examples to show the contrast:
- Sé que María viene mañana. (I know María is coming tomorrow.) — indicative (certainty)
- Dudo que María venga mañana. (I doubt María will come tomorrow.) — subjunctive (doubt)

When do I use the indicative?

Use the indicative when you present information as fact, when you believe it, or when you report something that seems true.

Typical triggers for the indicative:
- creer que (affirmative): Creo que él está en casa. (I think/believe he is at home.)
- saber que: Sé que ellos llegaron. (I know they arrived.)
- estar seguro de que: Estoy seguro de que vendrá. (I9m sure he will come.)
- es cierto que / es verdad que / no dudar que: Es verdad que hay tre1fico. (It9s true there is traffic.)
- parecer que (when used to state something that appears to be true): Parece que va a llover. (It seems it will rain.)

Note: When these verbs or expressions are negated, you often switch to the subjunctive: Creo que viene vs No creo que venga.

When do I use the subjunctive?

Use the subjunctive when the speaker expresses doubt, disbelief, denial, or treats the event as possible but not certain.

Common triggers for the subjunctive (expressions of doubt or uncertainty):
- dudar que: Dudo que tenga tiempo. (I doubt he has time.)
- no creer que: No creo que ella venga. (I don9t think she9ll come.)
- negar que: Niegan que exista el problema. (They deny that the problem exists.)
- no estar seguro de que / no parecer que: No estoy seguro de que estén listos. (I9m not sure they9re ready.)
- es posible/probable/improbable que: Es probable que llegue tarde. (It9s probable that he will arrive late.)
- puede que / puede ser que: Puede que llueva. (It may/might rain.)
- quizá(s) / tal vez / acaso / probablemente (often with subjunctive for more doubt): Quizás venga me1s tarde. (Maybe she9ll come later.)

Important note: Some of these expressions can also be followed by the indicative if the speaker treats the event as likely or almost certain. For example, "Es probable que este9 enfermo" (subjunctive for uncertainty) but in colloquial speech you may hear the indicative if the speaker feels more certain.

Common verbs and expressions (quick reference)

- Creer que: affirmative -> indicative. Example: Creo que Juan tiene razf3n. (I believe Juan is right.)
negative -> subjunctive. Example: No creo que Juan tenga razf3n. (I don9t think Juan is right.)

- Saber que / Estar seguro de que / Es cierto que -> indicative.
Example: Se9 que ella este1 aqued. (I know she9s here.) vs No estoy seguro de que ella este9 aqued. (I9m not sure she9s here.)

- Dudar que / No parecer que / Negar que -> subjunctive.
Example: Dudo que e9l venga. (I doubt he9ll come.)

- Es posible que / Es probable que -> usually subjunctive (but can use indicative if high probability).
Example: Es posible que haya tre1fico. (It9s possible there will be traffic.)

- Puede que -> subjunctive. Example: Puede que vengan me1s tarde. (They might come later.)
Note difference: Puede + infinitive -> possibility with infinitive: Puede llover. (It can rain / It may rain.)

- Quize1s / Tal vez / Probablemente -> can be followed by either mood. Subjunctive emphasizes doubt; indicative suggests greater likelihood.
Examples: Quize1s llueva. (Maybe it will rain e284 uncertain.)
Quize1s llueve. (Maybe it will rain e284 speaker treats it as more likely.)

How to form the subjunctive (short grammar)

Present subjunctive (used for present/future uncertainty):
- Take the "yo" form of the present indicative, drop the final -o, add the opposite vowel endings.
For -ar verbs: e, es, e, emos, éis, en.
For -er/-ir verbs: a, as, a, amos, áis, an.

Examples:
- hablar: hablo -> hable, hables, hable, hablemos, habléis, hablen.
- comer: como -> coma, comas, coma, comamos, comáis, coman.
- vivir: vivo -> viva, vivas, viva, vivamos, viváis, vivan.

Common irregulars (present subj.):
- ser -> sea; ir -> vaya; haber -> haya; estar -> este9; saber -> sepa; tener -> tenga; venir -> venga; dar -> de9.

Present perfect subjunctive (to talk about completed actions that are doubtful):
- Formed with present subjunctive of haber + past participle: haya + llegado, hayan + hablado.
Example: Dudo que haya terminado el trabajo. (I doubt he has finished the work.)

Imperfect subjunctive (used when the main clause is in the past):
- Start from the third-person plural of the preterite, drop -ron, add -ra, -ras, -ra, -ramos, -rais, -ran (or the alternative -se endings).
Example: hablaron -> hablara; comer -> comiera; ir -> fuera.
Example sentence: No creeda que viniera. (I didn9t believe he would come.)

Examples contrasting certainty vs doubt

- Certainty / Indicative:
Se9 que Mareda viene maf1ana. (I know Mareda is coming tomorrow.)
Doubt / Subjunctive:
Dudo que Mareda venga maf1ana. (I doubt Mareda will come tomorrow.)

- Certainty:
Creo que Juan tiene razf3n. (I believe Juan is right.)
Doubt:
No creo que Juan tenga razf3n. (I don9t think Juan is right.)

- Certainty:
Estoy seguro de que este1n en casa. (I9m sure they9re at home.)
Doubt:
No estoy seguro de que este9n en casa. (I9m not sure they9re at home.)

- Certainty:
Es cierto que hay problemas. (It9s true there are problems.)
Doubt:
No es cierto que haya problemas. (It9s not certain that there are problems.)

- Possibility with infinitive vs subjunctive clause:
Puede llover esta tarde. (It can/may rain this afternoon. e284 "puede" + infinitive)
Puede que llueva esta tarde. (It may/might rain this afternoon. e284 "puede que" + subjunctive)

- Modal adverbs (two moods possible):
Probablemente llegare1 tarde. (He will probably arrive late e284 speaker leans toward certainty.)
Probablemente llegue tarde. (He9ll probably arrive late e284 more doubt.)

- Past / completed action:
Se9 que ya llegaron. (I know they already arrived.)
Dudo que ya hayan llegado. (I doubt they have arrived yet.)

Common mistakes to avoid

- Using the indicative after verbs of doubt: *Dudo que e9l viene. -> Correct: Dudo que e9l venga.
- Using the subjunctive after affirmative creer/estar seguro: *Creo que venga. -> Correct: Creo que viene.
- Confusing "puede que + subjunctive" with "puede + infinitive": Use "puede que + subjunctive" for clauses (Puede que venga), but "puede + infinitive" when no "que" clause follows (Puede llover).
- Ignoring sequence of tenses: If the main clause is in the past, the subordinate clause usually moves to the imperfect/subjunctive: No creeda que viniera. (I didn9t think he would come.)
- Mixing English word order or relying on English moods: In English "I doubt he has come" uses indicative in the subordinate clause; in Spanish use subjunctive: Dudo que haya venido.

Short glossary

- Indicative: The mood for factual statements, beliefs, and things the speaker treats as real or likely.
- Subjunctive: The mood for doubt, uncertainty, wishes, hypotheses, and non-factual or unreal situations.
- Present subjunctive: Subjunctive form used for present or future uncertainty.
- Present perfect subjunctive: "Haya + past participle" used when you doubt or are unsure about a completed action (e.g., Dudo que haya llegado).
- Imperfect subjunctive: Subjunctive form used after past main clauses (e.g., No creeda que viniera).
- Main clause / subordinate clause: The main clause is the part of the sentence that gives the speaker9s attitude (e.g., Dudo...), the subordinate clause is the information affected by that attitude (e.g., ...que venga).

Quick summary

- Use the indicative when you state facts or strong belief; use the subjunctive when you express doubt, denial, or uncertainty.
- Many impersonal expressions that express possibility ("es posible que", "es probable que", "puede que") normally take the subjunctive e284 but can take the indicative if the speaker treats the event as likely.
- "Creer que" (affirmative) -> indicative; "No creer que" -> subjunctive.
- "Dudar que" -> subjunctive; "No dudar que" -> indicative.
- Pay attention to sequence of tenses: present main clause -> present subjunctive; past main clause -> imperfect/pluperfect subjunctive when appropriate.
- Practice recognizing the trigger (verb or expression) and then choosing the mood that matches the level of certainty you want to convey.