ABSTRACT
Our basic knowledge of the external world comes through the five senses: sight, hearing, touch, smell, and taste. For most of us the sense of sight plays the key role. I know what the world out there is like because I can see it. If I am uncertain whether what I see is really there, I can usually reach out and touch it to make sure. I know that there is a fly in my soup because I can see it, and, if it comes to it, touch it and even taste it. But what is the precise relationship between what I think I see and what is actually in front of me? Can I ever be sure about what is out there? Could I be dreaming? Do objects continue to exist when nobody is observing them? Do I ever have direct experience of the external world? These are all questions about how we acquire knowledge of our surroundings; they belong to the branch of philosophy known as the theory of knowledge or epistemology.
