Repetition of Prepositions

[fglorca]

I always spend my money on clothes and (on) books.

Is there a need to repeat the preposition a second time in each of the sentences below? In English there isn’t.

• Siempre gasto mi dinero en ropa y ‘en’ libros.
• Siempre gasta su dinero en libros o ‘en’ revistas.

[wrholt]

If the two (or more) nouns are perceived as being independent items, it is usual to repeat the preposition. However, if the two nouns are perceived as being components of one thing it is common not to repeat the preposition.

In the case of your examples:

Siempre gasto mi dinero en ropa y en libros, because clothes and books are not particularly related.

But: siempre gasto mi dinero en libros o (en) revistas,, because "on books or magazines" = "on stuff to read", but "en libros o en revistas" = "on (either) books or (on) magazines", viewing them as distinct classes of things.

[fglorca]

So, as carne and pescado are both food items in the sentence below, I can either include mucho before 'pescado' or omit it, and both options are grammatically correct?

I am a vegetarian and the family eats a lot of meat and fish:
• Soy vegetariano y la familia come mucha carne y pescado.
• Soy vegetariano y la familia come mucha carne y mucho pescado.

[wrholt]

The determining factor is whether you are talking about one thing (la carne y pescado = "animal muscle") or two things (la carne y el pescado = "mammal muscle tissue and fish muscle").

The nouns carne and pescado identify two types of foods at roughly the same level of categorization that together can describe a next-larger category as a single thing, "animal muscle".

The same thing happens with nouns for people: if you are talking about one person or one group, don't repeat prepositions or determiners, but if you are talking about more than one person or group, do repeat prepositions and determiners with each person or group.