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Thursday, January 26, 2006

"You can't prove a negative !"

"You can't prove a negative !". This is one of the most absurd and obtuse beliefs anyone could have about epistemology. Basic rationality, and basic science, goes completely against it. And yet throngs of skeptics and believers alike (two groups of people I have no love for) spout this nonsense as if it was a fait accompli.

Let me first state the obvious. Science progresses by proving negatives. More specifically, it is by constructing possible models of a phenomena (a hypothesis), and then testing them (falsification), that we advance and build on the knowledge that we already have. By doing so, we prove many negatives along the way. We came to the conclusion that oxygen is the necessary gas in burning because we were first able to disprove the existence of phlogiston, which was the reigning scientific position at the time. More exactly, we now say that oxygen is a better explanation of burning than phlogiston, because the first fits all the facts while the second does not.

In fact, it is considerably easier to prove a negative (or even a universal negative) then it is to prove a positive. To prove a positive requires extensive testing and decades or centuries of confirmation. To prove a negative can take only one experiment ! As soon as a piece of data disproves the proposition, the negative is proven. Of course, if a model fits most facts perfectly and only disagrees with a few facts, it may very well be that the model does not need to be trashed, but rather modified.

The idea of proving negatives by testing is also part of a basic epistemic principle, Occam's Razor. If you have two models explaining the same data, and one is simpler than the other, then the simpler one is true and the complex one is false.

The "can't prove a negative" contingent then tries to rationalize that away by saying that Occam's Razor is just a preference or a probability. This is nonsense. Occam's Razor is nothing more than a restatement of the fundamental rational standard that "to assert something you must have objective evidence". If you have two competing models, and one is more complex than another, then the complex ones has additional entities or processes which have no evidence to validate their existence.

Going over this, the "can't prove a negative" crowd will then try to remove the object of inquiry outside of human cognition. Here is a famous example, Carl Sagan's "The Dragon In My Garage" :

"A fire-breathing dragon lives in my garage"

Suppose (I'm following a group therapy approach by the psychologist Richard Franklin) I seriously make such an assertion to you. Surely you'd want to check it out, see for yourself. There have been innumerable stories of dragons over the centuries, but no real evidence. What an opportunity!

"Show me," you say. I lead you to my garage. You look inside and see a ladder, empty paint cans, an old tricycle -- but no dragon.

"Where's the dragon?" you ask.

"Oh, she's right here," I reply, waving vaguely. "I neglected to mention that she's an invisible dragon."

You propose spreading flour on the floor of the garage to capture the dragon's footprints.

"Good idea," I say, "but this dragon floats in the air."

Then you'll use an infrared sensor to detect the invisible fire.

"Good idea, but the invisible fire is also heatless."

You'll spray-paint the dragon and make her visible.

"Good idea, but she's an incorporeal dragon and the paint won't stick." And so on. I counter every physical test you propose with a special explanation of why it won't work.

Now, what's the difference between an invisible, incorporeal, floating dragon who spits heatless fire and no dragon at all? If there's no way to disprove my contention, no conceivable experiment that would count against it, what does it mean to say that my dragon exists? Your inability to invalidate my hypothesis is not at all the same thing as proving it true. Claims that cannot be tested, assertions immune to disproof are veridically worthless...


If a belief cannot be falsified in any way whatsoever, then what does it mean ? The meaning of a concept is a set of properties that we can use to differentiate between instance of that concept and other objects around us. The meaning of a table can be subsumed into these properties : furniture - flat horizontal surface - one or more vertical legs - used to eat on or support objects. I can use this meaning to look at different things and figure out whether they are tables or not.

Now if you present me a concept that is not falsifiable, such as the dragon, we cannot possibly extract any meaning from that concept. There is absolutely no way to distinguish it from anythnig else - in fact, that is its selling point ! So such talk is, like religious talk, complete gibberish that can only have significance for the individual within a specific inter-subjective context.

The case of the word "god" is very similar. "Weak atheists", agnostics and believers all try to push "god" into unfalsifiability. But as I said before, that makes it meaningless, and therefore disproven because of its inability to fulfill the smallest burden of proof. The other problem is that this unfalsifiability is plainly false, as the Problem of Evil and other atheistic arguments prove.

So where does this silly belief "you can't prove a negative" come from ? I think part of it is the impulse from American skeptics and atheists, who live in a country hostile to rationality and don't want to make more enemies than they need to, are very quick in deflecting possible conflict with believers. So they will adopt such a "tolerent" attitude even though it is completely irrational and destroys their own epistemology. And I doubt it actually helps much, since believers will always be convinced that we think they are wrong... and who can blame them ? They are obviously right in thinking that we do.

Post a Comment


26 Comments:

At 1/26/2006 12:55 AM, Blogger BlackSun declaimed...

Good point, Francois!

 
At 1/26/2006 10:02 AM, Blogger Zachary Moore declaimed...

I'd like to request a part 2 to this- how to handle those Christians who argue that "God did it" is the simpler way to explain the data. Perhaps an illustration of the complexity and contradiction of the God-concept.

 
At 1/26/2006 2:43 PM, Blogger Francois Tremblay declaimed...

Hmmm.

 
At 1/26/2006 4:20 PM, Blogger Dan Dufek declaimed...

I am curious, you are basically discussing falsification however Flew says in his interview with Gary Habermas that he went where the "evidence" led. Care to comment?

 
At 1/26/2006 4:33 PM, Blogger Zachary Moore declaimed...

streetapologist-

Flew only references two evidences in that interview. The first is Near Death Experiences, although he says that, "Where any such
near death experiences become relevant to the question of a future life is when and only when
they appear to show 'the occurrence of human consciousness independent of any occurrences in
the human brain.'" There's no citation of any medical or scientific evidence to bolster that claim.

The only other type of evidence he references (probably because of the interviewer) is the evidence for the Resurrection. But even there he says that, unfortunately "what we do not have is
evidence from anyone who was in Jerusalem at the time, who witnessed one of the allegedly
miraculous events, and recorded his or her testimony immediately after the occurrence of that allegedly miraculous event."

So perhaps this isn't the best source to present evidences for belief.

 
At 1/26/2006 4:43 PM, Blogger Dan Dufek declaimed...

I am not citing Flew as a source of evidence, per se. I was just curious what your (you and the others) take is on Flew's consideration of the "evidences" that caused him to reconsider his dogmatic commitment to atheism.

 
At 1/26/2006 4:47 PM, Blogger Dan Dufek declaimed...

This comment has been removed by a blog administrator.

 
At 1/26/2006 5:24 PM, Blogger Zachary Moore declaimed...

I would say that Flew's evidence (at least that which is mentioned in that interview) is very poor, as he seems to acknowledge.

Specifically as to the evidence for the Resurrection, I find it highly suspect that there are no independent corroborations by contemporary historians of the Christological events reported in the Gospels, especially the resurrection of the saints in Matthew 27:52,53.

 
At 2/06/2006 2:29 AM, Blogger Francois Tremblay declaimed...

I didn't express my point quite accurately. My point was not that OR is not probabilistic per se (as after all knowledge is probabilistic), but rather that it is not relatively MORE probabilistic than, say, logical deduction.

 
At 8/10/2006 11:44 PM, Blogger ~~~ Natasha !!! declaimed...

This comment has been removed by a blog administrator.

 
At 6/18/2007 4:46 PM, Blogger F. Bailey declaimed...

Carl Sagans "Dragon in the Garage" is the hight of foolishness. To assert the existance of something foolish in order to prove the non-existance of something else is tantamount to saying because Santa Clause does not exist neither do your parents. Just because science is bent on explaining away God through imperical devices does not negate the existance of socialogical, psychological, testamonial, natural, and logical evidences of His existance. Your correction of your OR argument is problematic in that you assume that logic is the only way to prove God. Logic does and will continue to prove God however the testimonial arguments from every culture and continent throughout history would certainly be stronger and more simple. I suppose that you would explain away all of the complexities of the human body and the cosmos as well as nature, as being more simply happenstance rather than intelligent design. It seems to me that you would have an easier time proving that you have a dragon in your garage. Especially since the dead Carl Sagan has given you the verbage for such an argument.

 
At 10/22/2007 4:03 PM, Blogger John declaimed...

F. Bailey says, "I suppose that you would explain away all of the complexities of the human body and the cosmos as well as nature, as being more simply happenstance."

No, I wouldn't. The complexities of nature are the result of evolution by natural selection, which is absolutely not random happenstance. Actually, evolution is un-intelligent design-- design which is guided by natural forces and dynamics, namely natural selection, or survival of the fittest. It's so easy to understand, and yet fundamentalists keep refusing to understand. Over time, small genetic mutations cause changes in physical traits of individuals. Harmful changes cause early death or the inability to find a mate. Other changes promote survival and mate attraction, and these changes get passed on to offspring and further propagated. This is evolution by natural selection.

Different species arise when a group of individuals from one species become geographically separated from the original population. Over millions of years, numerous small genetic changes accumulate in the separated population, until the genetic makeup of the two populations are so different that they can no longer have offspring together.

The massive evidence for evolution comes from many branches of science. Evolution has had an overwhelming consensus among all types of scientists, including millions of scientists who are Christians, for well over a hundred years, and no contrary evidence has ever appeared. There is no massive conspiracy to promote evolution. That's because evolution is true, and it doesn't need a conspiracy.

Evolution is supported by evidence. God isn't supported by evidence. No more, anyway, than is Sagan's dragon in the garage.

 
At 5/09/2008 1:38 PM, Blogger bobcarp declaimed...

Can one prove they've NEVER killed someone? Asking one to prove a negative is the height of foolishness and only a tool used by the frustrated who cannot prove what they themselves believe is in fact true. Dr. Sagan illustrates this foolishness expertly in his "Dragon in Garage" scenario. One can no more prove there is no dragon then one can prove there is no Jesus god or Hindu god or Islam god. One cannot prove the bible or Hindu writings or Koran IS NOT just the rantings of mortal man. Can a Christian prove an angel “DID NOT” appear before Mohammad and dictate the Koran? The burden for any rationally thinking, educated person should always be on the positive. Placing the burden on the negative lends to no academia to the discussion and is used only as a tool to reinforce ones already present personal beliefs.

 
At 7/12/2008 10:01 PM, Blogger Samuel Saltman declaimed...

I came upon this blog because I happened to think to myself today: "Wait! Isn't falsification -the bedrock of scientific inquiry -the same as 'trying to prove a negative'?" I'm not a scientist, nor am I religious; I consider myself a "natural philosopher," who follows Spinoza's school of thought that "God" is the totality of existence. I read another blog - http://skepticsplay.blogspot.com/2008/06/induction-vs-falsification.html - which argues that science is all about proving the negative, i.e. falsification. Now I'm sure I've misunderstood a ton of what I've read tonight, so forgive my being a neophyte. But, is this post basically saying the same thing, i.e. proving a negative is not only possible, but is also one and the same of falsification?

 
At 7/30/2008 11:07 PM, Blogger Unknown declaimed...

After hearing the phrase in question over and over from a number of professors, and wondering how the mainstay of positivism can exist alongside its opposite, I googled "prove a negative" and falsify, and landed here. I think you're completely right, but "a phenomena" is a linguistic atrocity. Please fix that.

 
At 12/08/2010 3:01 PM, Blogger Unknown declaimed...

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At 11/22/2011 7:10 PM, Blogger CCC declaimed...

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At 1/25/2012 6:46 AM, Blogger Paul Whitfield declaimed...

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At 5/19/2012 12:29 PM, Blogger PETER MORICE declaimed...

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At 8/29/2015 5:12 PM, Blogger NOBODY declaimed...

"God does NOT exist." Please, scientifically prove that. Thanks.

 
At 9/26/2017 8:12 AM, Blogger Unknown declaimed...

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