Wednesday, May 23, 2012

Please don't give me negative evidence

Positive and Negative Evidence

When people provide evidence to support a claim, that evidence breaks down into two basic categories - positive and negative evidence.

Positive evidence is useful, and negative evidence is useless, and I will attempt to explain why that's the case.

Positive Evidence

There's an object in my box.
  • It's white
  • It's spherical
  • It has a stitched pattern of two.. uh... maxi pads on it.
  • It's roughly 3" in diameter.
What is it? It's probably a baseball. We can say that with a high amount of confidence, especially when we get additional points of evidence. We can quickly formulate a high accuracy model of the object in question.

Negative Evidence

There's an object in my box.
  • It's not redish brown
  • It's not edible
  • It's not lighter than a marble
  • It's not made of metal
What is it? Would you still conclude it's a baseball? It's much more difficult to converge on the answer when all we have is a list of things it isn't. I could extend that list to a few ten thousand pieces of negative evidence, and we might be able to slowly converge on an answer, but it's impractical.

Positive evidence is sort of a process of elimination, but it's much better for the reason that there's a limited number of attributes of what the object is, and that there's an unlimited number of attributes of what the object isn't, therefore, it's much quicker to match up with it's positive traits.

It's Elementary, My Dear Watson

I made a passing reference to Sherlock Holmes in a previous post. I think it ties into this problem fairly well, because many people seem to follow a famous quote from Mr. Holmes:
"When you have eliminated the impossible, whatever remains, however improbable, must be the truth." The Sign of the Four, ch. 6 (1890) Sherlock Holmes in The Sign of the Four (Doubleday p. 111)
It's basically the process of elimination, right?

Within the context of my negative evidence example above, let's say that we had a list of possible objects - an American football, a banana and a baseball.

Based on the pieces of negative evidence, we can actually disqualify the football and the banana, leaving the baseball as the only possibility left.

Here's the problem. In the practical reality of investigating the universe, we don't have finite lists of possible answers. In fact, the phrase "the truth is stranger than fiction" is at the core of science. The more we dig in, the more bizarre the answers become (do some reading into quantum physics).

Thus, the negative approach doesn't really work.


Providing negative evidence is the single most common approach of apologetics. We'll extend the concept from simple attributes to larger pieces of evidence. Does any of this look familiar?
  • We've proven that evolution doesn't work, therefore there had to be a designer
  • Naturalism cannot explain beauty, therefore a God is required
  • Science can't explain how the universe came to be, therefore an all powerful being had to have done it.
Or, to contextualize it like I had with the baseball negative example: What is the answer to the origins of humans?
  • It's not evolution
How do you get from that to - therefore, Intelligent Design? That's right, you have to assume a finite list of possibilities - evolution and intelligent design.

They're all basically arguments from ignorance, but more to the point, they're trying to demonstrate a claim by showing what things aren't. More importantly, a lot of these arguments assume a limited number of possibilities, and make an even larger assumption that we know of all the possibilities. It fails as negative evidence for this reason.

Whereas, science is built upon positive evidence.
  • The red-shifting of the surrounding galaxies around us indicates that they're moving away (doppler effect), which indicates an expanding universe.
  • Genetics indicates that the more dissimilar a creature is from us, the more its DNA also differs from us, which corroborates common ancestry.
  • The Urey-Miller experiments showed that basic types of amino acids can spontaneously form under certain conditions, which is one of the steps along the way to abiogenesis, thereby supporting that theory.

Finite Possibilities

If evolution is proven to be false, then our status becomes "we don't know", not "therefore designer", because there may be another natural mechanism that satisfies the observations and actually works where evolution failed. We won't know until we investigate. 

It's the equivalent of "going back to the drawing board" - which doesn't imply that you have another answer ready to go.

Currently, as the debate tends to go, if we hypothetically disprove evolution, and the scientific community has to go back to the drawing board, there's an Intelligent Design proponent off to the side, hopping up and down, yelling "No no no no no - look! Look! I already have the answer right here! No! Come back! We don't need to go look for evidence or anything, I already have an answer!"

Well, no, you don't. Your answer must be positively demonstrated, before it's acceptable as an answer. To say it's either creation of evolution is a false dichotomy.

I mentioned before that positive evidence is "sort of" a process of elimination, but it's not really. We're venturing into the unknown. Science explores new territory, so there's not a whole lot of known possibilities to elminate. All we can do is build a model of what things we do know about a phenomenon. Science builds models of understanding (theory). It's not merely a process of listing out all known possibilities and then weeding out the bad ones (although that's part of it). We'd ever get anywhere with that approach.

Positive evidence, Mr. Watson. I need positive evidence!

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