Is this use of "det" out-dated?

[Debbie]

I have an old textbook (1980ish) that would have me translate "They are beautiful songs," as "Det er vakre sanger." The reason given is: "Det is used for all genders in both singular and plural when the noun is mentioned by name in the clause in which the word 'it' appears." Is this still true or is it an out-dated rule? It seems more natural to say, "De er vakre sanger."

Thank you.

[Olav]

Your book is right.

[Debbie]

I don't think I've found any sentences like that in Duo! Thanks for the feedback.

[anamorphism]

if the noun a pronoun represents hasn't been introduced into the context of the text or conversation yet, you always use the singular neuter form of the pronoun.

• det er ei god bok: it/that is a good book.
• dette er bøkene jeg leser akkurat nå. these are the books i'm reading right now.
• det er vakre sko. those/they are beautiful shoes.

but if using the words as determiners (coming right before the noun itself) then you'll match gender/count.

• den boka er god. that book is good.
• jeg leser disse bøkene akkurat nå. i'm reading these books right now.
• de skoene er vakre. those shoes are beautiful.

and you'll also match gender/count if the noun has already been introduced.

• jeg så en film i dag. jeg liker den. i saw a film today. i like it.

it's one of the more difficult things for native english speakers to learn since we always match count.