Missing article

Question

Hello,Why, for the translation of 'he is at his mother's house' is the spanish version 'el esta en casa de su madre' and not 'el esta en LA casa de su madre'? It feels strange that this article is dropped.Thanks!

Answer

Hola Patrick,
When we mention someone's house, generally someone we know or our own house we drop the article.

Estamos en casa. (We are at home [our home])
Vamos a casa de Luis. (We are going to Luis' house.)

This also implies that this house is where the person lives. 
However when "the house" is the direct object or is the subject of a sentence with "me gusta", we cannot omit the article. For example:

Me gusta la casa de Luis. (I like Luis´house.)
¿Has visto la casa de María? (Have you seen Maria's house?

I hope this helps.
Un saludo
Inma

Answer

Si. El auda.