Here’s the comment I left over there. I thought it worth posting here, too:
MD -
I’ll leave Randi to defend himself and his organization if he so chooses.
However, I will point out that you CAN prove a negative beyond a reasonable doubt and assign a probability to it.
There really isn’t such a thing as a “purely” negative statement, because every negative includes a positive, and vice versa. Thus, “there are no psychic monks in my closet” includes “this closet contains something other than monks” (in the sense that even “no things” is something, e.g. a vacuum).
“Something” is here a set restricted only by excluding monks, such that for every set S there is a set Not-S, and vice versa. In almost-English: Every negative entails a positive and vice versa.
To test the negative proposition one merely has to look in my closet: Since psychic monks being in my closet (p) entails that we would see monks when we look in my closet (q), if we find q false, we know that p is false. Thus, we have proved a negative.
Of course, we could be mistaken about what we saw, or about what a psychic monk looks like, or things could have changed after we looked, but within the limits of our knowing anything within reason, and given a full understanding of what a proposition means and thus entails, we can easily prove a negative in such a case.
This is not “proof” in the same sense as a mathematical proof, which establishes that something is inherent in the meaning of something else (and that therefore the conclusion is necessarily true–often 100% true based on numbers), but it is proof in the scientific sense and in the sense used in most courts of law. So my monk example holds because when p entails q, it means that q is included in the very meaning of p. Whenever you assert p, you are also asserting q. In other words, q is nothing more than an element of p.
Thus, all things being as we expect, “Bigfoot is in my kitchen” means if you look in my kitchen you will see Bigfoot, so not seeing him means the negative of “Bigfoot is in my kitchen.”
Negative statements often make claims that are hard to prove because they make predictions about things we are in practice unable to observe. For instance, the statement “there are no psychic monks” means that “there are no monks in this universe,” and unlike my closet, it is not possible to look in every corner of this universe, thus we cannot completely test this proposition. All we can reasonably do is look around within the limits of our ability and our desire to expend time and resources on looking, and prove that, where we have looked so far, and within the limits of our knowing anything at all, there are no psychic monks.
In such a case we have proved a negative, just not the negative of the sweeping proposition in question, and we can assign a probability to it. Obviously the probability of me seeing a psychic monk in my closet is quite low. On the other hand, assigning a probability to the existence of a psychic monk “somewhere” in the universe might be ill advised, because we do not have the ability to look “everywhere”. So, in that example I might suspend my judgment.
So, the Randi test or just about any other scientific test which has tested for “paranormal powers” has proven a negative, in my opinion.
So why is it that people insist that you can’t prove a negative? I think it is the result of two things: (1) Disappointment that induction is not bulletproof, airtight, and infallible, and (2) A desperate desire to keep believing whatever one believes, even if all the evidence is against it…
If we’re going to dismiss inductive arguments because they produce conclusions that are probable but not definite, then we are in deep manure. Despite its fallibility, induction is vital in every aspect of our lives, from the mundane to the most sophisticated science. Without induction we know basically nothing about the world apart from our own immediate perceptions. So we’d better keep induction, warts and all, and use it to form negative beliefs as well as positive ones.
You can prove a negative — at least as much as you can prove anything at all.
(Note: This post might change on this blog as I look back at it, review and reflect upon my logic, etc. )
