Conditional for conjecture about the past

Spanish uses the conditional simple not only to express hypothetical outcomes but also to make conjectural statements about the past — that is, to indicate that the speaker is guessing or estimating something that was true at a past moment. This is the past counterpart of the future of probability (which covers present guesses) and the future perfect of probability (which covers very recent past guesses). When the reference point is a more remote past, the conditional takes over: Serían las seis cuando llegó means «It was probably around six o'clock when he arrived» — a guess, not a fact.

Use the conjectural conditional when all of the following conditions are met:

• The situation belongs to the past. The moment you are guessing about is clearly located before the moment of speaking — often anchored by a preterite verb or a past time expression.

• You are expressing a guess, not a fact. You do not know the exact value (time, age, quantity, identity) and are estimating it. If you know the fact, use the imperfect or preterite instead.

• The reference point is not the immediate present. For guesses about the present, use the future of probability (Serán las once). For guesses about something that has just happened, use the future perfect (Habrá salido). The conditional covers the more remote past.

• Typical contexts include guessing the time at a past moment, estimating someone's age in the past, approximating a quantity or distance in a past narrative, and speculating about a past state or circumstance.

The conjectural conditional uses exactly the same form as the ordinary conditional simple. Take the infinitive (or the irregular conditional stem where one exists) and add the endings -ía, -ías, -ía, -íamos, -íais, -ían. These endings are identical for all three conjugation classes (-ar, -er, -ir).

• Using the future of probability with a past reference point.

  The future of probability is for guesses about the present. When the reference point is in the past, the conditional is required. Saying «serán las seis cuando llegó» mixes a present-tense guess with a past event, which is contradictory. The correct form is «serían las seis cuando llegó».

• Avoiding the conjectural conditional altogether.

  Many learners fall back on probablemente + imperfect (probablemente eran las seis) rather than using the conditional. While not incorrect, this is less idiomatic. A native speaker would typically say serían las seis — the conditional alone carries the probability meaning without any adverb.

• Mistranslating the conjectural conditional as «would».

  The conditional has two main uses in Spanish: the hypothetical («I would go») and the conjectural. When you see serían or tendría in a past narrative context with no si-clause or hypothetical frame, the correct reading is a probability estimate, not «would be». Tendría unos treinta años means «he was probably around thirty», not «he would be around thirty».