‘In the half’ and ‘in the middle’ are synonyms, right? They should be, but actually in English they are not.
‘In the half’ is not a phrase we use. While it is fine to say, ‘I cut the apple in half’ or ‘I divided the duties in half’, we cannot use ‘in half’ or ‘in the half’ to talk about a position in space or time.
Instead, we use ‘in the middle’. So if you have read around half of a book, you would say, ‘I’m in the middle of my book’ or if you have watched 1 hour of a 2-hour film, you could say, ‘I’m in the middle of the film’.
Alternatively, you can use another nice phrase – halfway through. This doesn’t work for things that are located in the centre of something. You can’t say, ‘My pen is halfway through the table’. It is not, it’s in the middle of the table. But for things like books and films or anything that involves a progression, it’s fine.
So, for today’s example about a book, you can say, ‘I’m am in the middle of the book’ or ‘I am halfway through the book.’