The conditional tense in Spanish is generally equivalent to the English construction “would + verb.” In Spanish, the conditional has five basic uses:
It roots a future action to the past. For example: Manuel me dijo que llegaría antes de las tres. (Manuel told me that he would arrive before three.) Pensaban que sus hijos no crecerían tan rápido. (They were thinking that their kids would not grow up so quickly.)
It allows for the hypothetical—with the implication that the conditional statement is unlikely. For example: Te compraría un pasaje a Europa, pero perdí todo el dinero en Las Vegas. (I would buy you a trip to Europe, but I lost all my money in Las Vegas.) Te ayudaría a mover el sofá, pero desgraciadamente me lesioné la espalda hoy por la mañana. (I would help you move the sofa, but unfortunately I hurt my back this morning.)
It gives room for a probability that is more expansive and may include conjecture or approximation. For example: Con quién hablaría Juan a esas horas de la noche? (With whom would Juan speak at that hour of night?) Serían las diez cuando la ví. (It might have been ten when I saw her.)
It allows for a concession in light of a contrary view or experience introduced by pero (but). For example: Sería tacaño pero nunca me negó su ayuda. (He might have been stingy but he never refused me his help) Ella tendría poca instrucción formal pero es una persona brillante. (She might have had little formal education but she is a brilliant person)
It provides an alternative to the copreterite in expressing a courteous request. For example: Podría decirme donde está la parada de autobús? (Could you tell me where the bus stop is?) Me dejarías usar tu teléfono? (Would you allow me to use your phone?)
The underlying idea to remember about the conditional is that the future is not so certain because what it depends on is either unlikely or too expansive to pin down and know readily.
The conditional tense also appears in “if/then” constructions that are posed in the past tense. For instance, in English you would say, “If I had a dog, I would take care of it well.” In Spanish, you would use the conditional for the “then” clause: Si tuviera un perro, lo cuidaría bien.
Conjugating verbs in the conditional tense is very easy, as long as you know the future-tense base. For regular verbs, that's simply the infinitive form, which you will use without dropping the –ar, –er, or –ir ending. (Irregular verbs will have the same base in the conditional tense as they do in the future tense. You will learn the irregular future conjugations in Chapter 15.)
The conditional endings are the same for all three groups of verbs. For some examples, take a look at the following table:
Conjugating Verbs in Conditional Tense