I´m a Computer Scientist with a new found interest in philosophy. In particular I'm interested in the philosophy of mind. I have two questions: 1) What is the big fuss about Frank Jackson's knowledge argument? I read the paper and found it quite silly - how could we ever imagine what it would be like to have all physical knowledge? How is it possible that this argument has generated so much debate? 2) Is it really that hard to imagine that we at some point will be able to build a computer that has a consciousness? I mean, apparently there is already such a machine - our brain! von Neumann said something cool once: "Tell me exactly what it is [consciousness] and I will build it". I believe him. In other words, how can there be so much controversy on this matter, when there is still no clear definition of what consciousness is? Thanks.

Jackson argues that even if you had complete physical knowledge of some conscious state -- such as the sensation of a color or a sound -- that you had never experienced --say because you were color blind, or deaf --you would still learn something new about that sensation if you went on to enjoy it yourself. Since you already knew all the physical facts about that experience and you learned new facts about it when you had the experience, there must be non-physical facts about it for you to have learned.

You make a legitimate response to this argument by questioning the assumption that you would learn something new if you had complete physical knowledge. Who knows? But I confess that I don't find this reply entirely satisfying. Although complete physical knowledge is a very different from our actual situation, I am moved by the fact that as I learn more purely physical facts about sensations these seem to tell me nothing about what experiencing that sensation is like, what it feels like, something I do know because I am not deaf or color blind. (All the physical facts I learn seem compatible with it not feeling like anything at all.) So maybe I'm gullible, but I do have the intuition that even complete physical knowledge would not give me everything. There are of course other ways to resist Jackson's argument, but I'm not going to try to summarize them here.

Even more briefly on your second question, the issue is not whether we could ever build a conscious thing: after all there is a sense in which men and women have been doing this for as long as there have been men and women. The issue is rather whether a computer would ever be conscious simply in virtue of the program it runs. And this is controversial. John Searle's famous Chinese Room argument is a provocative attempt to show that running a program is not enough, not for sensation, but for representational thought.

There are certainly philosophers who share your intuition about Jackson's thought experiment -- Daniel Dennett, for example, in Consciousness Explained claims that the problem with the argument is precisely the one you've pointed to: Jackson misimagines what it would be like to have all the physical information that there is.

On the other hand, I think many people do agree with Jackson that when Mary the color scientist leaves her black and white room and sees red for the first time, she will have an "Aha" moment -- "Aha, so that's what red looks like."

As an interesting side note: Jackson has recently recanted and he no longer thinks that this argument proves that physicalism is false. (Although his reasons for thinking that the argument does not succeed are different from yours.)

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