The Future and Conditional of Probability in Spanish

Here is a sentence that trips up every English speaker at first sight: ¿Qué hora será? Read it as a future tense and you get "what time will it be?", which is nonsense out of context - the time is not going anywhere. Read it the way a Spanish speaker means it and it is I wonder what time it is. The future tense here is not telling the time; it is guessing at it.

This is one of the great quiet workhorses of Spanish. The future and the conditional both moonlight as tenses of supposition: the future guesses about the present, the conditional guesses about the past. Where English scatters little words - must, probably, I bet, I wonder, will be - in front of an ordinary verb, Spanish bends the whole tense to the job. Once you see it, you cannot unsee it, and your spoken Spanish jumps a level.

Note the frame before we start: this page is not about the future and conditional as tenses of time. It is about the same forms doing a completely different job. Será the time-teller and será the guess are spelled identically; only context, and often a question mark, tells them apart.

The core idea: future guesses the present, conditional guesses the past

Line the two up and the system is almost insultingly simple.

The ordinary relationship between the two tenses carries straight over: the future points at now, the conditional points at then. All that changes is that instead of stating a fact about that time, you are hazarding a guess about it. Keep that pairing in your head - future = present guess, conditional = past guess - and everything below is just examples.

The future of probability: guessing about the present

Take an action happening now that you are not sure about, and put its verb in the future. The tense itself now means "probably" or "must be".

• ¿Qué hora será? (I wonder what time it is. / What time can it be?) - not "will it be".
• Serán las tres. (It is probably three o'clock. / It must be three.)
• Estará en casa. (He is probably at home. / He must be at home.)
• Tendrá unos treinta años. (He must be about thirty.)
• ¿Quién será a estas horas? (Who on earth can that be at this hour?) - the doorbell rings.
• Estarán cenando. (They are probably having dinner right now.) - future of the present continuous.

Every one of these is about the present moment. Nobody is talking about the future at all. The English translations reach for must, probably, I wonder, can it be - the future tense in Spanish rolls all of those into the conjugation. The question forms (¿qué hora será?, ¿quién será?) are especially common: they are how Spanish muses aloud, the spoken equivalent of a raised eyebrow.

The conditional of probability: guessing about the past

Now shift the guess back in time. An action that was going on in the past, guessed at rather than known, takes the conditional.

• Serían las tres cuando llegó. (It must have been about three when he arrived.)
• ¿Qué hora sería? (I wonder what time it was.)
• Estaría cansado. (He was probably tired.)
• Tendría unos treinta años entonces. (He must have been about thirty then.)
• Habría unas cien personas en la sala. (There were probably about a hundred people in the room.)
• No contestó; estaría durmiendo. (He did not answer; he was probably asleep.)

Set serían las tres against serán las tres and the whole system snaps into focus. Serán guesses at the present - it is probably three now. Serían guesses at the past - it was probably about three then. Same verb, one letter of difference in the ending, and the guess slides from now to then. This is exactly why learning the pairing beats learning the two uses separately.

The conditional of probability loves an approximate number. Serían las tres, habría unas cien personas, costaría unos veinte euros - the tense is doing the work of "about", "roughly", "something like", telling you the speaker is estimating a past quantity, not counting it.

Guessing about finished actions: the compound forms

Push both tenses into their compound forms - haber plus a past participle - and you can guess about completed actions, not just ongoing states.

Future perfect: a completed action with present relevance

The future perfect (habrá + participle) guesses that something has happened by now.

• Habrá llegado ya. (He must have arrived by now.)
• Ya habrán terminado. (They have probably finished already.)
• ¿Habré dejado las llaves en casa? (I wonder if I have left the keys at home.)
• No lo veo; se habrá ido. (I do not see him; he must have left.)

The action is finished and its result matters now - the classic present-relevant perfect - but layered with a guess. Habrá llegado is to ha llegado exactly what estará is to está: the same tense, tilted from statement to supposition.

Conditional perfect: a guess about the further past

The conditional perfect (habría + participle) guesses that something had happened at an earlier point in the past.

• Habría salido antes. (He had probably left earlier.)
• Para entonces ya habrían cenado. (By then they had probably had dinner.)
• No estaba; habría ido al médico. (She was not in; she had probably gone to the doctor.)

This is the deepest layer: a guess about a past-before-the-past. It stands to the pluperfect (había salido, he had left) as the conditional of probability stands to the imperfect - the certain version made into a supposition. Do not confuse it with the conditional perfect of the third conditional (habría salido si..., he would have left if...); here there is no si, and the meaning is "probably had", not "would have".

The four forms on one card

Put all four together and the symmetry is the thing to memorise.

Read the right-hand column top to bottom and you have the entire probability system: present guess, past guess, completed-present guess, completed-past guess. The forms are ones you already know as tenses; all you are adding is the second job.

The plain-spoken alternative: deber de + infinitive

If bending a tense to mean "probably" feels too slippery, Spanish gives you an explicit alternative that says must out loud: deber de + infinitive.

• Deben de ser las tres. (It must be three.) = Serán las tres.
• Debe de estar en casa. (He must be at home.) = Estará en casa.
• Debía de estar cansado. (He must have been tired.) = Estaría cansado.
• Debe de haber llegado ya. (He must have arrived by now.) = Habrá llegado ya.

Deber de plus an infinitive is pure supposition - the meaning the future and conditional of probability carry, spelled out in words. There is a textbook distinction worth knowing even if speakers blur it in practice: deber de = supposition (debe de ser tarde, it must be late, I reckon), plain deber = obligation (debe ser puntual, he has a duty to be punctual). In real speech many people drop the de and say debe ser las tres for the guess; the careful, exam-safe form keeps the de for a supposition. Either way, if a future-as-guess ever risks being read as a genuine future, deber de is the unambiguous way to say the same thing.

Worked examples

• Suena el telefono. - ¿Quién será? (The phone rings. - Who can that be?) - present guess.
• No está aquí. Estará en el trabajo. (He is not here. He is probably at work.) - present guess.
• Serían las once cuando volvieron. (It must have been about eleven when they got back.) - past guess.
• Estaba pálido; estaría enfermo. (He was pale; he was probably ill.) - past guess.
• Llama otra vez, ya habrá salido de la reunion. (Call again, he must be out of the meeting by now.) - completed-present guess.
• La casa estaba vacía; se habrían mudado. (The house was empty; they had probably moved out.) - completed-past guess.
• Deben de ser las tres, tengo hambre. (It must be three, I am hungry.) - the deber de alternative.

Common mistakes English speakers make

Reading será as a genuine future. The single biggest trap. ¿Qué hora será? is a guess about now, not a question about later, and estará en casa means he is probably home, not he will be home. Let context and the question mark steer you: a future-tense verb about the present moment is almost always a supposition, not a prediction.

Adding "probably" on top of the tense. Because the tense already carries the guess, you do not also need probablemente. Estará en casa already means "he is probably at home"; probablemente estará en casa is not wrong but it is doubled up. Trust the tense to do the work.

Mixing up será and sería. Future for a present guess, conditional for a past guess. Serán las tres (it is probably three now) and serían las tres (it was probably three then) are one letter apart and a whole time frame apart. Get the time of the guess right and the tense follows.

Confusing the conditional of probability with the "would" conditional. Estaría cansado can mean "he was probably tired" (probability) or "he would be tired" (conditional proper); habría salido can mean "he had probably left" or "he would have left". Only context and the presence or absence of a si clause tell them apart. If there is no if-then in sight, suspect probability.

Forgetting deber de for clarity. When a bare future or conditional would be ambiguous, the tense is not your only option. Deben de ser las tres says "must be" out loud and cannot be misread as a future. Reach for it when you want the guess to be unmistakable.

Stop reading será and serían as times, start reading them as suppositions, and remember the pairing: future guesses the present, conditional guesses the past, with the compound forms guessing about finished actions and deber de standing by as the plain-spoken version. That is the whole of one of the most useful tricks in spoken Spanish.

See also

• The future tense - the forms you already know for tomorrow, here moonlighting as the tense of guessing about today.
• The conditional - the would tense, which doubles as the tense of guessing about the past.
• si clauses - where the conditional and conditional perfect do their other job, the would and would-have of hypotheticals, not to be confused with probability.
• The Spanish grammar cheatsheet has the future-guesses-present, conditional-guesses-past pairing on one card.