When is definite article needed to contract with de

I am confused as to when you need to include the definite article in expressions, when contracted with “de”. For example, why is it “a rede de metro”, but “a casa da musica”?

@pvreed, usually both are possible, but with nuances in meaning. As a general rule of thumb, when we don’t add a definite article, the expression sounds more general or abstract, and adding a definite article to it makes it sound more specific, as if you were singling out an element, even when you’re basically talking about the same thing in both cases.

For example, we can say both “rede de metro de Lisboa” and “rede do metro de Lisboa”, but the second seems more focused.

“Casa da Música” is a slightly different example - it’s the given name of a concert hall in Porto, and the name somewhat personifies music as this single specific inhabitant of this single specific house. Just like how we say “casa do Pedro”, “casa da Joana”… not “casa de Pedro/de Joana”. On the other hand, we say “casa de fados” when referring to any of the several venues where fado is regularly performed. There’s no specificity there. We also say “escola de música” to describe any music school, for example.