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I understand that al is a combination of a + el when used before a noun, however in what situations would you use it in front of a verb, for instance

'Al llegar al tercer semaforo...'

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Possible duplicate of:… – Alfredo Osorio Apr 27 '13 at 2:30
in spanish, "el llegar" would also kind of make sense in the sense of "el evento de la llegada". This is just not to be compared to english at all. – Sebas Apr 27 '13 at 19:52
@Sebas I think that what you are saying is the real origin of this use of "al"! – Sironsse May 2 '13 at 10:51

"Al" is mostly used when you are going to use "when" (and some other times "upon"), and it should be used before a verb. The verb must be on the infinitive form (this means that it's not a personal form of the verb, and ends with "-ar", "-er" or "-ir".

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Doesn't cuando mean when? – 0x499602D2 Mar 14 '14 at 21:51

En este caso, esta locución en un sustituto de la forma "cuando" o "en cuanto", que, de forma popular, se sustituyen en España por "a la [ocasión de] que + verbo" o "a lo que + verbo".

Cuando él llegó al tercer semáforo. = A la que él llegó al tercer semáforo. = Al llegar él al tercer semáforo.

En cuanto miré me di cuenta. = A la que miré me di cuenta. = Al mirar me di cuenta.

Debe usarse siempre con infinitivo, o bien con un verbo pronominal si la frase lo lleva, por ejemplo:

Cuando me lo dijo me fui. > A la que me lo dijo me fui. = Al decírmelo me fui.

Me gustó en cuanto me vi con él. = Me gustó a la que me vi con él. = Me gustó al verme con él.

En cuanto lo miré me di cuenta. = A la que lo miré me di cuenta. = Al mirarlo me dí cuenta.

Uso de "al" en este contexto explicado en la RAE:

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In this context al is not a contraction of the preposition a and the definite article el, but a preposition in its own right.

When used before a verb in the infinitive (like in your example), the preposition al is used like the English preposition upon or on in the same context. It could aternatively be translated by a phrase such as at the time of.

That is to say, it is used to introduce an something which occurs simultaneously with, or immediately after, the action described by the verb.

So to take your example,
'Al llegar al tercer semaforo...' = 'Upon arriving at the third traffic light...'
Meaning that when the subject arrives at the third traffic light, '...' will happen.

Another example might be
'perdió el equipaje al cambiarse de tren' = 'he lost his luggage when he changed (or at the time of changing) trains'.

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For what it's worth, the second al in your example is a contraction of a el. Confusing as it may be, the two al s are entirely different words. – Caesar May 15 '13 at 22:56
I never heard of this use of al. Thanks for teaching me something new. – Flimzy May 20 '13 at 22:31
I heard it a lot in Spain, but I don't know if it's used as much in South America... Can anyone comment? – Caesar May 22 '13 at 5:19

"Al llegar" is the same as "cuando llegues", which means "when you reach".

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The OP is not really asking the meaning of "al llegar", but the use of "al". – JoulSauron Apr 29 '13 at 8:44

The easiest interpretation that works 99% of the time is "upon + verb"


"Al cambiarse la ropa" = Upon changing his/her clothes...

"Al ir al baño" = Upon going to the restroom...

"Al besar a la chica" = Upon kissing the girl...

Al most always be followed by the infinitive, but it works well in a surprising number of instances and can make your sentences quite flexible.

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You can think that "al llegar" is a propositional phrase in which "llegar", being an infinitive, is used as a name, because of the article "el". The preposition "a" gives this construct an adverbial taste.

But we also use other prepositions: - "Con el batir de palmas, el actor salió de escena" - "Entre el ir y venir, ya no sé ni dónde estoy" - "Hasta el andar me quita el aliento"

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