What is the mental world? The mental world is the world in our heads. It is the way in which we perceive the world; it consists of our sensations, feelings and thoughts. It is a completely subjective world. In the theory of the three worlds, the mental world is the third world besides the physical and the Platonic worlds. Difference from the physical world Whereas the physical world is objectively comprehensible, the mental world remains subjective. In other words: whereas we can observe the objects of the physical world from the outside, this is impossible with the objects of the