  Mentalism is broader than PI because it does not restrict the justifiers to justified beliefs, nor even to beliefs. So, mentalism but not PI is perfectly compatible with a view that says that sensory states that are themselves not beliefs and not things that can be appropriately said to be justified can nonetheless function as justifiers. A very simple example that illustrates the difference would be one in which a person acquires a justified belief that there is a tomato in front of her on the basis of a perceptual experience of something looking red and spherical. Mentalism can allow that this very experience of something looking red and spherical is a justifier for the belief that there is a tomato present. For PI, by contrast, if this experience is to contribute to the justified tomato belief, it would have to be because one has a justified belief about something appearing red and spherical. In short, mentalism allows that the very experience may count as a justifier, while PI requires that a justified belief, presumably about that experience, is the appropriate justifier.