The simple conditional expresses hypotheses, courtesy, softened advice and estimates about past or future events from an imagined point of view. It also appears in indirect speech to situate a future action relative to a past, such as when reporting something said earlier. Its central value is not certainty, but possibility seen from a condition, a softened intention or a conjecture.

The simple conditional is formed by adding the endings -ía, -ías, -ía, -íamos, -íais, -ían to the full infinitive. This same base is used with all regular verbs and also with many irregular verbs in the simple future. The relationship with Simple Future is visible because they share a very similar verbal base.

Many verbs change the stem before adding the endings of the conditional, and that irregular stem coincides with the future simple. Among the most frequent are moods of verbs of great everyday use such as decir, hacer, poder, poner, querer, saber, salir, tener, venir and haber. These forms are very productive in hypotheses, courtesy and probability.

The simple conditional expresses a contrafactual situation when combined with if and the imperfect subjunctive. The basic structure is if plus imperfect subjunctive and, in the other clause, simple conditional. To better understand the relationship between both forms, it helps to relate it to the Subjunctive Mood, which provides the unreal or doubtful condition.

The simple conditional softens requests, desires and proposals, so it sounds more distant and polite than a direct formulation. In this sense it is often used with wanting, liking and other expressions of necessity or convenience, and the word quisiera is often preferred as a particularly courteous form. These formulas are used together with pronouns and complements to reduce the force of the request.

The simple conditional also softens recommendations and suggestions, so the advice sounds less imposing than with the imperative. In this use appear mainly should, could and other modal expressions that present the recommendation as prudent or reasonable. The resulting sense is one of guidance, not order.

The simple conditional is used to estimate past events when information is incomplete and deduction is based on hints. In this use it equates to a conjecture such as would be three o'clock or would be tired, and expresses an approximate evaluation. In some contexts, the conditional perfect may appear more frequently for past hypotheses, especially in certain regional varieties.

In indirect style, the simple conditional expresses a future seen from a past. Therefore in a past narrative it appears to reproduce a promise, intention or event that had not yet occurred at that moment. This relationship is well understood by comparing it with the Perfect Conditional, which places the anteriority relative to that past reference point.

The conditional perfect is formed with the conditional of haber plus the participle, and preserves the relation of anteriority relative to a hypothetical or past point. The auxiliary comes first and the participle follows the general rule for participles, with endings ado or ido. The placement of clitics can vary depending on whether the simple or compound form is used, but the basic verbal structure remains.

The simple future presents a fact as planned or certain from the present, while the simple conditional presents it as hypothetical, courteous or estimated from a perspective dependent on another condition or a past narrative. When the main idea is the certainty of what is to come, the future is chosen; when the softened possibility, the suggestion or the conjecture matters, the conditional is chosen. That is why both forms look similar in their verbal form, but they are clearly distinguished by their communicative value.