In text, 'I believe in you.',What is the meaning of 'in'?

Solution 1:

  1. “I believe you” means I believe what you are telling me is the truth. I may not have any actual proof but I trust you. You might say this to someone who says they haven't committed a particular deed or act.

A: Did you break this vase?
B: No, mom. It was the dog, he knocked it over by accident.
A: Okaay, I believe you.

  1. “I believe in you” means I have faith in your abilities, I will support your ambitions and dreams.

to believe in something is a phrasal verb, there is no reason as to why it is the preposition ‘in’, and not for example, ‘of’, but the phrasal verb acts like a single meaning, and perhaps that is a good enough reason.

Common beliefs with ‘I believe in are: Santa Claus, ghosts, magic, ‘love’, science, God, or any deity, etc.