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Classic Text #2

A Defense of Skepticism

Peter Unger

Peter Unger is one of the more ardent contemporary advocates of philosophical skepticism. His book, Ignorance, presents a series of arguments defending skeptical positions. In this, Unger joins one of the longest traditions of philosophical thought. "Skepticism" comes from the Greek word skeptikos meaning "inquirers". Indeed, the doubt and challenge accompanying skeptical attitudes has been sometimes credited as the motive force behind the evolution of ideas. The word "skeptic" has been applied throughout history to anyone who doubts and challenges authority, dogma, and common opinion. Thus, skeptics have included those who challenge religious authority and popular beliefs.

True skeptics are not merely doubters. To merely have doubts and a propensity to challenge others may well be just a stubborn lack of sensitivity. True skeptics use reason to explain and advance their ideas; they have arguments. This is important because it helps to distinguish the philosophical skeptic from the mere "denier" who flatly rejects all evidence and argument to the contrary of their own view. Holocaust deniers, conspiracy theorists, and amoralists often fall into the category of the mere denier. Philosophical skepticism sets for itself a standard of reason at least as rigorous as that it applies to other positions. Consistency is always important to the skeptic. Thus, if you find someone smugly challenging the views of others with expressions of doubt or demands for ever increasing proof, you have found a dogmatic denier rather than a true skeptic.

In A Defense of Skepticism, Unger examines a classic skeptical argument: the appeal to logical possibility. Something is logically possible when there is no logical contradiction in saying it. For example; "All white sheep are not white" is a contradiction; it denies what it affirms, while "All white sheep are not mammals" is not a contradiction at all; even though it is false. The falsity of a contradiction consists entirely in the claim itself, and not the relatin of the claim to the world. We can check the truth of "All white sheep are not mammals" by observing some sheep and noting that they are, in fact, mammals. We cannot do the same for the contradictory claim. Contradictions are internal.

Unger is specifically interested, in this passage, with skepticism about the external world. The external world is contrasted with our perceptions. Much (if not all) of what we believe about the world derives from our experience of it. Some philosophers hold that all of our beliefs, or even ideas and thoughts, come from experience. We commonly suppose that the sources or causes of our experiences are material objects. The external world is the existence of such objects. One of the defining characteristics of the external world is that it exists independently of any experience or perception whatever. That is, if rocks exist in the external world, then they exist whether they are being perceived or not. But if something exists only while it is being perceived by someone, then it does not belong to the external world.

We commonly make the distinction from something being "in reality" and being "in your head." Hallucinations and fantasies are usually thought of as "in your head." Saying so does not deny that the experience is real or that the causes of the phenomenon are real. To be "in your head" denies that the phenomenon exists independently of its being experienced. When a person stops having a fantasy, it is not as if the fantasy continues to exist independently waiting for the next person to have it. We typically regard material objects as different from things that are "in your head." They exist "outside of our head" as well, in the external world.

Skeptics raise questions about how we can know that the objects in the external world exist at all. Perhaps everything that exists is completely a perception and nothing else. The problem is, how could we tell the difference? Unger proposes an "exotic case" in which our perceptions are caused by something quite different from material objects in the external world. His case of an evil scientist who controls all of our perceptions by brain implants is based directly on the Evil Demon argument proposed by Descartes. You may agree that if you are under the control of the evil scientist, then what you believe about the external world is not really known by you at all. In this case, the world is more like a sustained hallucination. It is not public and external world.

Unger agrees that this case is bizarre and extremely improbable. It is not, however, logically impossible. Thus, we cannot know that it is false. However strong our belief in material objects and however direct our perception of them seems to be, it remains possible that we are actually perceiving something entirely different. So long as that possibility remains, knowledge does not.

One of the most powerful sources of arguments against skepticism about the external world is in the work of G.E. Moore. His "A Proof of the External World" article is long and exacting, but it has stood as perhaps the strongest challenge to this sort of skepticism in the twentieth century. Moore begins his argument by seeking a clear analysis of concept "external object"; he want to have a definite understanding as to what we the skeptic is denying we have knowledge of. It takes determined effort to follow Moore's analysis. Unger does not consider this analysis, but goes straight to Moore's conclusion: that he really does know that there is an external world. This is not a satisfactory reply to Moore and no one should feel that they understand or can refute Moore's argument from having read Unger's account.

One crucial thing that Unger does not do is to explain what he means by knowledge. He puts it in italics to emphasise something, but he does not explain what it means. The concept of knowledge here is so central to Unger's whole project that getting clear about it is not optional. He does address the concept of knowledge in other parts of his writing. But what does he mean by it here? One clue is to look in the "Ordinary Cases" section of the piece. he cites cases such as "knowing that a certain city is the capital of a certain state" and "reporting a known fact". These cases are useful because they give us uses of "know" that we can work from in making sense of what he means. Unger treats the ordinary cases as similar in some way to the exotic cases;

"in either case, no matter whether you are right in the matter or whether wrong, thinking that you know manifests an attitude of dogmatism."

It is possible to be wrong about a state capital or a fact, even when it seems absolutely certain that you do know. Likewise, it is logically possible that what we believe we know about the external world is quite wrong. Even with these cases, it is mandatory for the serious skeptic to take up the issue of what is meant by "know" and "knowledge". Otherwise we can never be sure of what is being challenged at all.

In reading Unger's essay, keep these questions in mind:

  • What does Unger mean by knowledge?
  • What would be required of a belief to say that you know it?
  • What are exotic contrast cases and how do they function in the skeptical arguments?
  • How does the evil scientist example lead to doubt?

It may be valuable for you to browse some related resources. This is not a fixed assigment (the Unger paper is). Rather, these are resources that can assist in connecting with the key ideas and in finding examples of them in practice. Please let us know how these resources do or don't help.

Peter Unger
The Author

The Brain in the Vat
A nice presentation of this classic problem.

Cartesian Skepticism
If the Brain in the Vat interests you, be sure to investigate it's origins with Descartes, who you will be reading soon.

The Matrix
The latest movie (in a long list) based on the classic skeptical hypothesis. Compare this movie's premise to the "brain in the vat" problem that Unger describes. If you use this site, I suggest you get the Flash 4 plugin and go for it.

Theory of Knowledge Notes
G. J. Mattey

A relative of skepticism that holds that we can only know that we exist, so we may well be entirely alone in the universe. What do you think?


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