>> 1. Suppose, that there are basic empirical beliefs, that is, emperical
>> beliefs (a) which are epistemically justified, and (b) whose
>> justification does not depend on that of any further emperical
>> beliefs.
>> 2. For a belief to be episemically justified requires that there be a
>> reason why it is likely to be true.
>> 3. A belief is justified for a person only if he is in cognitive
>> possession of such a reason.
>> 4. A person is in cognitive possession of such a reason only if he
>> believes with justification the premises from which it follows that
>> the belief is likely to be true.
>> 5. The premises of such a justifying argument must include at least
>> one empirical premise.
>> 6. So, the justification of a supposed basic empirical belief depends
>> on the justification of at least one other empirical belief,
>> contradicting 1.
>> 7. So, there can be no basic empirical beliefs.
>> (3) circle back upon itself in some way.
There is a seemingly absurd way to doubt the "givenness" of sense
data;
Dr. Know & the Braino Helmet
Imagime that a superscientist invents machine--we shall call it a
"braino," - that enables him to produce hallucianations in certain
subjects . The machine operates by influencing the brain of a subject
who wears a special cap, called a "braino cap." when the braino cap is
placed on a subject's head, the operator of the braino can affect his
brain so as to produce any hallucination in the subject that the
operator wishes. The braino is a hallucination-producing machine. The
hallucinations produced by it may be as incomplete, systematic, and
coherent as the operator of the branio desires to make them.
The present argument starts from the premise that the braino is a
logical possibility, and consequently that there should be
hallucinations that are coherent, complete, and systematic in every
way. From the premise of logical possibility, we conclude that we in
fact have no way of telling whether or not we are hallucinating.
If the braino is a logical possibility, then how can we tell that
hallucinations are not in fact so hard to detect? On the contrary, we
may suffer hallucinations that we cannot detect. If it is logically
possible that hallucinations should be coherent, complete, and
systematic in every way, then there is no way of detecting at any
moment that we are not suffering from a hallucionation.
How we can tell that we are not hallucinating. The braino argument is
intended to establish that we can never tell this, even if we can
sometimes tell that we are hallucinating. Consider some perceptual
belief that you would maintain does not from hallucinations. what
experiences guarantee this? Indeed, what experiences provide you with
any evidence of it?
Notice that whatever experience you indicate, the braino argument will
be quite sufficient to prove that such an experience is no guarantee
against hallucianation. All we need do is imagine that you have,
unknown to yourself, the braino cap on your head. the operator of the
braino is producing the very experiences you claim guarantee that you
are not hallucinating.
Imagine that all people are controlled by the braino and that the
machine is run by some evil being, Dr. Know, who plots to keep us
completely in error through hallucinations. Dr. Know does not wish to
be detected, so he supplies hallucinations that are coherent,
complete, and systematic. Indeed, the hallucinations he produced in us
are a PERFECT COUNTERFEIT OF REALITY.
Our experiences fulfill our expectations and contain no more surprises
than we would expect from reality. But is it not reality we
experience; our perceptual beliefs about the world are quite mistaken,
for the source of our experiences is a mere machine, the braino, which
creates hallutionations. In such a predicament we might have just the
sort of perceptual beliefs we now have, based on experiences exactly
similar to those we now have. But our perceptual beliefs would be
altogether false.
The imagined situation is exactly similar to ours with respect to the
reasons or evidence we would have for our perceptual beliefs.
Experience is virtually the same in both cases. Consequently, if we
lack knowledge in one situation, we must surely lack it in the other.
Obviously, we lack knowledge when we are controlled by the braino, for
then our perceptual beliefs are false. Hence, we also lack knowledge
in our present situation. More precisely, our perceptual beliefs fail
to constitute knowledge in either case.
We believe that we are not controlled by such a machine, and if we are
fortunate in this belief, then no doubt many of our perceptual beliefs
are true. It is, however, good fortune and not good evidence that we
should thank for correctness of these beliefs.
We are just lucky if there is no Dr. Know controlling us with a
braino; and from that good fortune may result the further good fortune
that most of our perceptual beliefs are true. it is just a matter of
luck, however, and nothing epistemologically more glorious than that.
If a belief is true as a result of luck, then it is a lucky guess--not
knowledge.
Adapted from Keith Lehrer
Philosophical Problems and Arguments: An Introduction
by James W. Cornman, Keith Lehrer, George Sotiros Pappas
http://www.amazon.com/exec/obidos/tg/detail/-/0872201244/
http://books.google.com/books?id=cRHegYZgyfUC&printsec=frontcover
