knowledge by sensory perceptions
The third way we can know things is through sensory experience. Here, we are moving away from certainty because, as Descartes said, it is possible that our senses are deceiving us. Here is where I agree with Nietzsche in his criticism of some philosophers. The ironic thing, though, is that it is actually eastern philosophers who doubt the existence of the external world. Hindus think everything is maya, that is, illusion. Western philosophers generally accept the existence of the external world, so what Nietzsche’s real problem should be is with the fact that some western philosophers think the physical world is not all there is in reality. Here we notice something interesting. If we assume that our senses are giving us true information about the world, then what do we base that knowledge on? Do we base it on our sensory experience? No, we base it on our intuition. We just assume our senses are giving us true information. So those who claim that we can only have knowledge through our senses are making a self-refuting claim since their claim is not known through their senses. Since the claim is self-refuting, we know that it is false. Since it’s false, it cannot be the case that sensory experience is the only way we can know things. Intuition is the other way we can know, and we could not know anything through our senses if it were not for intuition to tell us that we should trust our senses.
But should we trust our senses? I think so. One of the arguments used against relying on our senses is the fact that we dream and the fact that we hallucinate. But look at it this way. If we are in a constant state of delusion, then how would we ever know that we had been hallucinating before or that we had been dreaming before? The only way we can know that is if we are not dreaming or hallucinating now. The fact that we make a distinction between dream and reality shows that we are not always dreaming. We are not always delusional.
Should we trust our intuition when it tells us to trust our senses? I think so. I asked one person in class whose name I can’t remember whether he thought it was more reasonable to believe that the world is maya or to believe the world is real. He said he didn’t prefer one over the other. But how many of you would walk out into moving traffic and ask, “What is reality anyway?” I suspect that when it comes down to it, you all believe very strongly in the physical world. And what reason is there not to? While it may be possible that we are being deceived, the fact that it is possible does not mean that it’s reasonable to believe. The external world stares us in the face every day, but the theory that the world isn’t really there is contrived. It’s just made up. Nobody lives consistently with the belief that the external world is an illusion because no matter how much we deny the physical world, we all live in it, and we all believe in it.
At this point, we can see how we are moving from certainty to doubt. Some of those things we knew intuitively are actually more certain that what we can know of the physical world. There is one last way of knowing that I’ll mention, and although it is said by some to be the most reliable way of knowing, it is actually the least reliable because it depends on the previous ways of knowing for it’s foundation. That is inductive reasoning.
[In a debate I had a couple of years ago, the person I was debating with said we can trust our senses, because everybody else around us is observing the same thing. If I see a green jeep, and everybody around me sees the same thing, then I should trust that my perception of the green jeep is accurate.
But this argument is question-begging. How do we know that there's anybody around us that sees what we see? Well, we can only know that through our senses. We have to see these other people, and we have to hear them when they tell us they see the same thing. The only way we can appeal to other people is if we assume already that our senses are giving us true information about the external world, and that begs the whole question.
Another person might say that our different senses themselves give us multiple attestation. If our nose, ears, eyes, and hands, all agree that the green jeep is there, I should trust them.
But this argument fails, too, because all of our sensory experiences take place in one and the same mind. When we dream, we see people talking and hear their voices at the same time, and yet it all goes on in the mind. If all of our senses are in question, then we can't appeal to any of them to justify the others. And we can't appeal to consistency either, because our mind produces consistent perceptions even when we're dreaming.]