This could be another person, a tree, food, etc. Another way we are able to see the external world is by connecting an idea that corresponds to the real world, known as the correspondence theory. For example, if two large plants that have big leaves, look similar, and we know from previous experiences that it is a palm tree, we can infer that it is in fact a palm tree. When an idea about what is going on in the world corresponds to what is actually going on in the world, knowledge results. So therefore, knowledge is based on our experiences of the world. This is a valid theory of what knowledge is because it makes sense to a great extent. If I am trapped in a closet for the majority of my life, I probably will not know anything other than the inside of closets and what is surrounding me in that closet. This theory explains why some people undoubtedly have more knowledge than others, they have more experience. It also explains why we disagree on things, we have different experiences of the world. .
Another prodigious philosopher is Rene Descartes, who objects the realist theory. Descartes tried to distinguish what he is certain about and what he is not. He believes if you are certain about something than you should not have any doubt. But if you have any doubt, then you do not really know. He also points out that if you destroy the foundation of something, it will in turn fall apart. Descartes analyzed the realist theory with this idea. The foundation of the realist theory is the five senses. If you destroy the senses, the realist theory will fall apart because our senses deceive us about things that are far away and indistinct. A common example of this is when you are driving and in the distance, your eyes deceive you to believe that there is a puddle of water in front of you. But when you approach the puddle, it disappears. Not only do we have doubt in things that are far, we have doubt in things that are right in front of us.
