Using 'Al' Followed by an Infinitive

The use of the contraction al followed by an infinitive is a very common way of indicating when something happens.

Al followed by an infinitive is usually the approximate equivalent of "upon," "on" or "when" followed by the gerund (the "-ing" form of a verb) in English.

Here are some examples of this usage:

• El diagnóstico se hace al encontrar que hay dolor. (The diagnosis is done upon finding that there is pain.)
• Hay error al enviar mensajes desde mi programa de correo. (There is an error when sending messages from my email program.)
• Lea en la mañana al despertarse; lea en la noche al acostarse. (Read in the morning on getting up; read in the evening when going to bed.)
• Al comprar una empresa, la consideración más importante es sus aspectos económicos. (When buying a business, the most important consideration is its economic aspects.)
• Me puse nervioso al ver la osa con su cría. (I became nervous upon seeing the bear with her cub.)
• Al escuchar el himno nacional todas las personas quitarán el sombrero. (On hearing the national anthem, all the people will take off their hats.)

The translations given above are all fairly literal. If you were translating such sentences in real life, you'd probably rephrase in some cases in order to get more natural English:

• Hay error al enviar mensajes desde mi programa de correo. (I get an error when I send messages from my email program.)
• Me puse nervioso al ver la osa con su cría. (I became nervous when I saw the bear with her cub.)