One common way of saying in Spanish that if A happens, then so will B is to use si, the equivalent of the English "if": Si hace sol, voy a la playa. If it's sunny, I am going to the beach.

Sentences such as these are fairly easy for beginning Spanish students, because they generally use the indicative mood.

However, Spanish also uses various phrases to mean something similar to si or "if," and they typically require use of the subjunctive mood.

Such phrases — they're common in English as well — are known as expressions of condition or, more technically, subordinators of condition. Most common are the following, given with possible English translations, although since they all have similar meanings they often can be used interchangeably. As usual, context will determine the best translation to use.

• a condición de que — on condition that
• bajo la condición de que, bajo condición de que — under condition that
• con la condición de que — on condition that
• con que — providing that (In different contexts, con que or con qué can also mean "with which" or "with what.")
• con tal que, con tal de que — provided that
• en caso de que — in case
• siempre que — whenever (Siempre que is often followed by a verb in the indicative mood when it refers to the past or to ongoing events that are habitual or frequently repeated.)
• siempre y cuando — provided that (This phrase is the most emphatic of those listed.)

Note how in the following examples the phrase is followed by a verb in the subjunctive mood, as is sometimes (but not always) the case in English.

• El sondeo dice que los estadounidenses están a favor de inmigración a condición de que no aumente. The poll says Americans are in favor of immigration as long as it doesn't increase.
• Renovó su contrato hasta el final del 2018 bajo la condición de que su hija permaneciera en el equipo. He renewed his contract until the end of 2018 on condition that his daughter remain on the team. (This is an example of the English subjunctive being used in translation.)
• Las bibliotecas prestan libros con la condición de que estos sean devueltos en el mismo estado. The libraries loan out books on condition that they are returned in the same condition.
• Se necesita empleado con que tenga sus propios herramientos. An employee is needed provided he has his own tools.
• Trabajamos con tal de que nos ayuden con este asunto. We will work provided you help us with this matter.
• ¿Qué hacemos en caso de que la E. coli llegue a México? What do we do in case E. coli arrives in Mexico?
• Siempre que enseñes, enseña a la vez a dudar de lo que enseñas. — José Ortega y Gasset. Whenever you teach, teach at the same time to doubt what you're teaching. — José Ortega y Gasset.
• La constitución consagra la libertad de culto, siempre y cuando la práctica de una religión no infrinja la moralidad, la decencia o el orden públicos. The constitution establishes freedom of religion when and only when the practice of a religion doesn't infringe on public morality, decency and order.

Sources: As with many lessons on this site, sample sentences are adapted from a variety of sources, generally ones written by native Spanish speakers. Among the sources consulted for this lesson are: Buenas Tareas, CNN Mexico, Municipalidad de Liberia, MundoAnuncios, Noticias 24, Terra.com, Univision.