Skepticism. Skeptics doubt that we can have knowledge. Actual skeptics are rare. In spite of the fact that few people endorse skeptical theories, skepticism is important to philosophy because it is a tool for thinking about what knowledge really is. There are many Types of Skepticism:
Global Skepticism. We don’t know anything! We can’t know anything! Unfortunately for a global skeptic, he or she would not be able to know that global skepticism is true.
Local Skepticism. I may be able to know some things, but there are other things that cannot be known. In other words, there are fields of study about which we can have no knowledge. For example, a local skeptic may think that we can have knowledge about math and science but not about whether things are beautiful.
Skepticism about ability to know vs. skepticism about our ability to have a justified belief. It is different to claim that we cannot know anything than it is to claim that we have no reason to justifiably believe. The person who thinks that we cannot have justifiable belief does not rule out the possibility for knowledge. Knowledge is still possible in principle. The person who thinks we cannot know thinks that knowledge is in principle impossible.
Skepticism about the External World. One has skepticism about the external world if he or she believes that there is insufficient evidence for our beliefs about the external world. There are three presuppositions of external world skepticism: (1) Everything we know, we know through the senses, (2) The external world could be different than I experience it and I would not be able to tell the difference & (3) The external world is mind-independent. A good example of skepticism about the external world is the "brain in a vat" scenario: Imagine that you are really a brain in a vat in the lab of a mad scientist. This mad scientist is just making you think that you are having all kinds of experiences! In this case,
Descartes’ “Dream Argument”. In his work Meditations on First Philosophy, Descartes divides his work up into six sections, called meditations. In the first two, Descartes uses skeptical arguments to destroy the foundations of knowledge so that he can build a new, more solid foundation for knowledge. In the first meditation, Descartes provides reasons for skepticism based on the similarities between dreams and waking life. He notes that there are times when we think we’re doing something (like sitting and reading) but really, we’re dreaming. He says that there are no “sure signs” that we can use to tell the difference between being awake and dreaming. Because of this, we could be dreaming at any time!
Dream Argument Revamped. Although Descartes himself only writes about the first two premises of this argument, we can expand on his thoughts on dreaming in order to construct an argument for skepticism based on the nature of dreams:
1. Some dreams are indistinguishable from waking life. Some dreams seem just like being awake.
2. So the way an experience seems cannot be used to decide if I am awake or asleep. The qualitative characteristics of an experience are not good indicators of whether I am awake or dreaming.
3. If I can’t trust the way my experiences seem to me, then I can’t know that I’m not dreaming now.
4. So I can’t know that I’m not dreaming right now.
5. If I can’t know for certain that I’m awake now, then I can’t know for sure that I’m ever awake.
6. I can’t ever know if I am actually every awake. I could be dreaming all the time!
7. If I could be dreaming all the time, then any belief based on an experience could be false.
8. Therefore, none of my beliefs based on experience can be counted as knowledge.
Challenges to the Dream Argument
Premise 1: Some philosophers claim that the first premise is false because there are indicators that we can use to reliably tell the difference between being awake and dreaming. A skeptic would respond by saying that premise 1 is true even if there are only a few dreams where it is impossible to tell the difference between being awake and dreaming.
Premise 3: Some think that we can tell that we are not dreaming by using something other than the way an experience seems. They think that if I can judge or have a reasoned opinion that I am awake, then I must be awake. A skeptic would respond by saying that you could just be dreaming that you are judging!
Premises 4, 5 and 6: Some say that there is a flaw in the logic of this argument, since premise 6 does not logically follow from premise 4. They will say that just because any experience could be a dream does not mean that every experience could be a dream. The skeptic would respond that because it is possible that I am dreaming right now, my memories about having been awake in the past are not reliable. So I really don’t know if I’ve ever been awake!
Premises 6 and/or 8: Some philosophers think that we can only be said to be mistaken if we are also sometimes correct. We could only recognize dreams or deceptions if we had the ability to distinguish dreams and deceptions from reality. In other words, it is only possible to decide if a belief is based on error if we already have a way of deciding if a belief really is based on error. These views represent a view called Verificationism, which is the view that in order to know something, we must be able to verify it. We cannot verify the skeptical thesis. In other words, we would have no way to know for certain that the skeptical thesis is true.