Conditional of Probability | Portuguese (Portugal) Grammar

Portuguese has a quietly elegant way of speculating about the past: it uses the simple conditional to mean "must have been," "was probably," or "would have been around…" This is the exact mirror of the future of probability, which uses the simple future to speculate about the present. Where English deploys must, probably, and maybe to hedge, Portuguese can do it with the verb form alone. The effect is more compact and often more literary than the modal alternatives.

This use of the conditional is not hypothetical. Nothing is being imagined. The speaker is making a real claim about what actually happened, but acknowledging that they don't know for sure.

The basic pattern

Seriam umas dez horas quando ele chegou a casa.

It must have been around ten o'clock when he got home.

The speaker is not saying "it would be ten o'clock if…" — there is no condition. They are saying the real time was approximately ten; the conditional adds the hedge. English translates this with must have been or was probably, but Portuguese expresses the uncertainty directly in the verb.

Teria uns cinquenta anos, mas parecia mais novo.

He must have been around fifty, but he looked younger.

Estaria cansado da viagem quando adormeceu no sofá.

He must have been tired from the trip when he fell asleep on the sofa.

Haveria umas vinte pessoas na sala, no máximo.

There must have been about twenty people in the room, at most.

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The quickest way to spot this use: if the sentence sounds like a guess about a past situation, and there is no se-clause, the conditional is expressing probability, not a hypothesis. Translate with must have been, was probably, or would have been (in the estimation sense).

Mirror image of the future of probability

To feel the symmetry, compare the two:

	Future of probability (present)	Conditional of probability (past)
Time	Que horas serão?	Que horas seriam quando chegaste?
Age	Terá uns cinquenta anos.	Teria uns cinquenta anos.
State	Estará cansado.	Estaria cansado.
Quantity	Haverá umas vinte pessoas lá.	Haveria umas vinte pessoas lá.

Que horas serão? — Present speculation: what time is it right now?

What time could it be? / I wonder what time it is.

Que horas seriam quando ele saiu? — Past speculation: what time was it when he left?

What time could it have been when he left? / I wonder what time it was.

Portuguese keeps the relationship neat: present-tense speculation uses the future form; past-tense speculation uses the conditional form. Time marches backward by one step.

Register: where you actually hear this

This is a literary and formal use, far more common in newspapers, novels, and careful writing than in daily speech. A journalist describing a crime scene, a novelist painting a character's past, a historian reconstructing an event — these are the natural homes of the conditional of probability. In everyday conversation, Portuguese speakers often prefer the modal construction devia ser / devia ter + past participle instead.

Seria umas três da manhã quando ouvimos o barulho. (literary / written)

It must have been around three in the morning when we heard the noise.

Devia ser umas três da manhã quando ouvimos o barulho. (everyday spoken)

It must have been around three in the morning when we heard the noise.

Both sentences mean the same thing. The first is what you read in a novel; the second is what you say to your friends over dinner. See dever for probability for the modal alternative.

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If you want to sound literary, write seria, teria, estaria. If you want to sound natural in conversation, say devia ser, devia ter, devia estar. Both convey probability; the choice is register.

Journalism and historical writing

The conditional of probability is beloved in Portuguese journalism. It lets a reporter signal that a detail is not verified without having to insert possivelmente or alegadamente every sentence.

O suspeito teria fugido pelas traseiras do edifício, segundo testemunhas.

The suspect reportedly fled through the back of the building, according to witnesses.

O encontro ter-se-ia realizado numa casa particular em Sintra.

The meeting reportedly took place in a private house in Sintra.

O acidente teria ocorrido por volta das duas da manhã.

The accident is thought to have happened around two in the morning.

Note how this use of the conditional corresponds closely to English reportedly, allegedly, or is said to have. A reader recognizes immediately that the newspaper is citing unverified information.

Common estimations and approximations

The conditional of probability is particularly natural with round numbers, ages, times, and quantities — places where speech would hedge anyway.

A reunião duraria umas duas horas, no máximo.

The meeting must have lasted about two hours, at most.

Ela seria a pessoa mais velha naquele jantar, ainda assim era a mais divertida.

She must have been the oldest person at that dinner, and yet she was the most fun.

O quadro valeria uns cinquenta mil euros naquela altura.

The painting must have been worth about fifty thousand euros at the time.

A casa teria pelo menos duzentos metros quadrados — era enorme.

The house must have had at least two hundred square meters — it was enormous.

The conditional perfect variant

When you want to speculate about something that was completed before another past event — more like English must have been or would have been in a perfect sense — use the conditional perfect: teria + past participle.

Teria sido por volta das dez quando começou a chover.

It must have been around ten when it started to rain.

O Pedro teria saído antes de nós chegarmos — a luz da cozinha estava apagada.

Pedro must have left before we arrived — the kitchen light was off.

Já teriam jantado, a julgar pelos pratos na banca.

They must have already eaten, judging by the dishes on the counter.

The distinction is subtle and often interchangeable with the simple conditional:

Simple conditional	Conditional perfect
Seriam dez horas.	Teria sido por volta das dez.
It must have been ten. (state)	It must have been around ten. (completed estimation)

For more on the conditional perfect, see Conditional Perfect Overview.

Spoken European Portuguese leans heavily on devia / devia ser / devia ter for past probability. This is the modal of inference — corresponding almost exactly to English must.

Devia ser muito cedo quando ele saiu.

It must have been very early when he left.

A Ana devia ter uns trinta anos na altura.

Ana must have been about thirty at the time.

Devia estar exausto depois de tanto trabalho.

He must have been exhausted after so much work.

The choice between seria / teria / estaria and devia ser / devia ter / devia estar is essentially one of register:

Function	Conditional (formal)	Devia + infinitive (everyday)
estimation of time	Seriam umas dez.	Deviam ser umas dez.
estimation of age	Teria uns cinquenta.	Devia ter uns cinquenta.
inferred state	Estaria cansado.	Devia estar cansado.
inferred quantity	Haveria cem pessoas.	Devia haver umas cem pessoas.

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Both forms are correct and both are used. In written Portuguese — newspapers, novels, history essays — the conditional dominates. In spoken Portuguese, devia is far more common. If you are unsure in conversation, default to devia.

Comparison with English

English has multiple ways to hedge about the past — must have been, would have been, was probably, might have been, seemed to be — and Portuguese collapses these into a single verbal strategy: shift the verb to the conditional. The downside is that the conditional does triple duty (hypothetical, politeness, probability), so the reader has to infer the meaning from context. In practice, context almost always makes the intent clear:

Conditional + se-clause = hypothetical (se tivesse, compraria).
Conditional + polite frame or request = politeness (gostaria, preferiria).
Conditional + factual past context with no se = probability (seriam dez horas).

English speakers should also note that would have been in English sometimes expresses probability (he would have been about fifty) and sometimes a past hypothetical counterfactual (he would have been happier there). Portuguese distinguishes them: the probability use is teria uns cinquenta anos, while the counterfactual uses a se-clause: teria sido mais feliz se…

Common Mistakes

❌ Seria dez horas. (intended: it's probably ten o'clock right now)

Incorrect tense — speaking about the present, not the past.

✅ Serão dez horas. (present probability)

It must be around ten o'clock.

✅ Seriam dez horas. (past probability)

It must have been around ten o'clock.

The conditional speculates about the past. For present speculation, use the future: serão, terá, estará, haverá.

❌ O suspeito teria fugir pelas traseiras.

Incorrect — used bare infinitive where past participle is needed.

✅ O suspeito teria fugido pelas traseiras.

The suspect reportedly fled out the back.

When using the conditional perfect (teria + past participle), make sure to use the participle (fugido, saído, chegado), not the infinitive.

❌ Ele teria cinquenta anos se estivesse vivo. (probability reading)

Ambiguous — this form is usually counterfactual, not probability.

✅ Ele teria uns cinquenta anos na altura. (probability, clear)

He must have been about fifty at the time.

Avoid pairing the conditional of probability with a se-clause, which flips the reading to hypothetical. Use time-marking phrases (na altura, naquela época, quando aconteceu) to keep the probability reading clear.

❌ Em conversação casual: Seriam umas três da manhã quando ouvi um barulho.

Technically correct, but sounds bookish in casual speech.

✅ Em conversação casual: Deviam ser umas três da manhã quando ouvi um barulho.

It must have been around three in the morning when I heard a noise.

In spontaneous speech, default to devia. Reserve the conditional of probability for writing or deliberately formal contexts.

❌ Acho que chegaria mais cedo. (intended: I think he probably arrived earlier)

Incorrect — the conditional doesn't fit after *acho que* with a past meaning.

✅ Acho que chegou mais cedo. (fact)

I think he arrived earlier.

✅ Acho que teria chegado mais cedo. (probability, formal)

I think he must have arrived earlier.

After expressions of personal opinion like acho que, use the indicative for straightforward belief. Reserve the conditional for genuinely uncertain speculation about the past.

Key takeaways

The simple conditional expresses probability or conjecture about the past: seria, teria, estaria, haveria.
This is the mirror of the future of probability, which does the same job for the present: será, terá, estará, haverá.
Translate the conditional of probability with English must have been, was probably, would have been (about), or — in journalism — reportedly and allegedly.
This use is literary, written, and journalistic. In everyday speech, prefer the modal devia ser / devia ter / devia estar.
The conditional perfect (teria + past participle) serves the same function for completed past events: teria sido por volta das dez.
Context disambiguates: a se-clause signals hypothetical; a polite frame signals politeness; a plain factual past context signals probability.
Do not use the conditional of probability for present speculation — that is the job of the simple future.