We have books on biology?
To say this in spanish is it necessary to add the article or can it be omitted?
Tenemos libros en biología.
or
Tenemos los libros en biología.
1 Answer
You don't use the article here
Also, the preposition "on" has meanings that "en" can't express in Spanish, like the one you tried to use. For that, we use "de" or "sobre":
on relating to: a book on pregnancy. Her thesis is on Italian women's literature.
Cambridge Advanced Learner's Dictionary
de prep. Denota asunto o materia. Este libro trata de la última guerra. Una clase de matemáticas. Hablaban de la boda.
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In other words, if you can replace "on" by "related to", and still means the same, you have to use "de", and not "en".