Why "Il écrit à sa tante" becomes "Il lui écrit"?

Question

During the lesson it is explained to use lui/leur when you have the "à" before the object and to use la/le/les when there is a possessive pronoun before, for example:

"Il va appeler ses parents" --> "Il va les appeler"

So why using lui in this case?

Cécile Janty-Davies · Accepted Answer

Hi Vitor,
If I can explain with two verbs which, in French, mean the same thing, to ring someone.
You can use the verb, téléphoner à quelqu'un' ( please note the à of the lesson )
Je vais téléphoner à mes parents ------> Je vais leur téléphoner 
I am going to ring my parents -----> I am going to ring them
But if you use another verb 'appeler quelqu'un' for, to ring someone
(note: no -à )
You will then use direct object pronouns -
https://french.kwiziq.com/revision/grammar/when-to-use-le-la-l-or-les-to-replace-nouns-direct-object-pronouns
Je vais appeler mes parents ----> Je vais les appeler
The only difference is the little preposition  'à' .
Hope this helps!

Sean Burke · Answer

You write "to" someone. In French, it is "Il écrit à sa tante." So, the indirect object is "lui" both for men and women. But, it's weird because certain verbs are different. You don't say, "Je lui pense." Instead, you say "Je pense à lui" or "Je pense à elle" or "Je pense à toi." I chalk the whole thing up to languages develop in fits and spurts and often do not make sense. There are general rules, but also plenty of exceptions. I suppose that's the whole challenge. In your native language, you just choose what "sounds right." That's harder to do in a target language, at least for me.