On + book

On + book
 

To me, Americans use on more often than in; is it correct to use on even when we are not talking about something sci-fic?

-There is a alien __ his French books.

If not sci-fic, could you think of any reason to justify on? I can't think of one, because even when you are talking about things on the cover, you don't use on; you use in: in the picture of the cover.

The preposition 'on' is used to indicate position on top of something physical.
It can also be used to specify where something virtual can be found, such as 'on a web page'.

"There is an alien on the book." The alien is standing or is seated or is drawn on the book's cover (or the upper surface of its binding).

"There is an alien in the book." The story written in the book mentions an alien.

"There's an alien on the cover (of the book)."
"There's a dog on the cover."
"Look at this flower on the cover."

"There's a dog on the book." There is a dog standing or seated or drawn on the book's cover or binding.
"There's a dog in the book." The story mentions a dog.

Sci-fi (no 'c' on the end)

Excellent answer. Thank you.