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From: laura@utzoo.UUCP (Laura Creighton)
Newsgroups: net.sci,net.philosophy,net.misc
Subject: Re: science and belief
Message-ID: <4150@utzoo.UUCP>
Date: Sun, 29-Jul-84 14:07:02 EDT
Article-I.D.: utzoo.4150
Posted: Sun Jul 29 14:07:02 1984
Date-Received: Sun, 29-Jul-84 14:07:02 EDT
References: <2980@ecsvax.UUCP>
Organization: U of Toronto Zoology
Lines: 56

This ``absence of evidence is not evidence of absence'' bit: I
think that it is only one way of stating that it is not possible
(in the general case) to prove a negative. 

The best way to try to prove a negative is to set something
up which goes:

	p implies not-q
	q therefore not-p

(Try to prove that my class is not full of 7-up.

	glass full of 7up implies glass not full of coke
	glass full of coke, therefore glass not full of 7up)

Now the way that you would like to set this up to prove that
PSI does not exist is:

	existence of PSI implies some sort of physical evidence
	no physical evidence therefore no PSI

You notice that the form of the argument, (Denial of the Consequent)
is the same. However, in the first example I could point to the existence of
something and conclude from that. Here I am stuck with trying to prove
``no physical evidence'' which is a tougher proposition.

Even if there has been no evidence whatsoever, there is always the
possibility that there will be some tomorrow. 

However, we cannot all make like the Red Queen and believe 7
impossible things before breakfast. At some point you  need to
set a threshhold and say ``unless there is more than this much
evidence I am going to assume for the moment that not only is there
none but there isn't going to be any either.'' Of course, having
done this you have to remember why it is that you are disbelieving
something so that if somebody comes by with a heck of a lot of
evidence that goes over the threshhold then you will reexamine
the evidence.

This is necessary. Otherwise I will have to keep thinking that
``there might be a big hairy monster in my sock drawer that eats
my socks -- even though I haven't seen it (yet)'' and anything else
I could possibly imagine.

To balance this problem is the generally accepted claim that the
people who are trying to present a new theory have to provide
the evidence. And if the claim is extrodinary, then then evidence
had better be extrodinary as well. It may be that there is extrodinary
evidence for PSI that we either don't know how to recognise yet, or
haven't found for some other reason. But, until the people who are
interested in such things actually present this evidence, there is
no more reason to believe in PSI than there is to believe in
my sock monster. 

Laura Creighton
utzoo!laura