tification. Anything that does not fall into this category is a belief justified by something outside the first person or yourself. Beliefs about the external world need justification. The easiest way to explain this theory is to put it in a dialogue or "dialectic" form. Like a conversation between two people where one person proposes an idea or theory and the other person tries to reinforce or find fault in the other persons reasoning. For simplicity's sake let's say that I had the following dialogue with Joe, the guy with the dog on the mat.Joe: Hey Craig, my dog is on the mat. I see that my dog is lying on the mat. And sensing any physical object through one or more of my five senses has to guarantee that the object is in fact there in the real physical world.Craig: Wait a minute Joe, just because you are having sense data of the dog does not mean the dog exists in the real world. Let me explain, what you are seeing is a mental (electrical) representation of a dog on a mat. In your dreams you see, touch, taste, smell, and hear things. Are they real? I don't think so. I cannot doubt that you are having the sensory data, that is a self-justified belief. I can think of another possible scenario of you seeing the dog on the mat. You are actually dreaming, all this is empty space. Your belief cannot be justified because I have developed another scenario that could account for your sensory data. Therefore, since sense data does not guarantee the conclusion of an external world knowledge of that external world is impossible.Joe: Fine, I can't guarantee that there is an external world out there based on my senses. But I can say there there probably is an external world out there. I am currently sensing the dog on the mat, and most of the time when I have sensed something, it has really existed. I am usually not dreaming therefore, there is a dog on the mat.Craig: Once again Joe, I have to point out to you the error in yo...
