How Do We Know if We're Having Experiences?

How do we know there's an extra mental world at all? Writers kind of like am to extreme version of the concern. But aquinus doesn't take that rout, because he doesn't think of cognition er lemental as being somehow set outside his philosophy of nature. And so his answer to the question lie, what are our relationships and what secures our relationships to the outside? Those are the things that are going to underwrite for him the reliability of our perceptions.