Friday, 2 November 2012

Explaining Evidence

In On Evidence, I mentioned an exchange between Humble Don and the Shaved Chimp:

Humble Don (HD): It’s theoretically possible that you could be presented with enough evidence to argue you to a different position …

The Shaved Chimp (SC): Oh, sure.

(HD): At which point, you would begin to intellectually doubt Christianity …

(SC): Well, yes, what, wh-what, what those arguments would have to do is explain the evidence better …

(HD): Right.

(SC): … than the Christian claim.

I only briefly touched on it, but this “explain the evidence” seems to be a recurring theme, so I thought I might look more closely at it.

Note closely the shift in focus away from evidence to argument and then to explanation of the evidence.

What the Shaved Chimp seems to be alluding to is a comparison between one claim (the Christian claim) and an opposing claim.  This is fair enough given that they were talking about a newspaper piece by an atheist.  So Humble Don was suggesting that it is theoretically possible to be presented with enough evidence to argue the Shaved Chimp into assuming an atheist position.

Imagine that archaeologists open a cave to find a treasure trove of documentation including early versions of the gospel according to Mark that deviate significantly from the published version, with copious notes indicating that the story is based not only on the “messiah phenomenon” that is common in Judea but also elements of the mythology of India, Egypt, Mesopotamia and Assyria together with some Greek storytelling techniques.  The documentation, dated to before 50CE (via a comprehensively documented event that led to the sealing of the cave), makes absolutely clear that the author considered the story to be fiction and there is no scientific reason to doubt the validity of the documentation.

Can this evidence be explained by the “atheist claim”?

Well, not really.  Why were the documents written?  Unless there’s a documented explanation we simply don’t know why the author wrote them.  We do know that various authors throughout history have written fiction for entertainment or to make some point.  Someone with an atheist inclination might posit that the author had wondered what would happen if the child of a god were to be born into the world of the day (there are plenty of people who believe that if a Jesus like figure was around today, he’d be eliminated rather swiftly).  Such a theory, however, is not an explanation rooted in the “atheist claim”.

Can this evidence be explained by the Christian claim?

Sure, no problem.  The Holy Spirit moved in the world then as it does now.  While the author known as Mark might not have thought that the story was true, the fact that the Holy Spirit selected someone who did not believe the story is immaterial.  The intent of the Holy Spirit in selecting Mark was to ensure the best possible rendition of the Gospel, to express a higher truth than that perceived by Mark himself.


If your focus is entirely on explaining evidence as it arises, then the Christian claim can always suffice.

The sorts of people who actively seek out evidence (atheists, legitimate scientists and materialists) aren’t looking to explain evidence.  They also have a higher standard when it comes to what constitutes evidence.

The idea that the scientifically inclined don’t try to explain evidence might have Christian apologists snorting into their beards so I had better explain.

In the scientific method, one tries to explain observations, not evidence.  Science, as a method, attempts to integrate our knowledge into a seamless whole.  What science does not do is simply list the observations and then attempt to explain them individually.  As Sean Carroll says in The Great Debate – Has Science Refuted Religion? – “the dumbest, but most accurate, scientific theory would just be a list of everything that ever happened, everywhere in the universe”.  Science sacrifices this level of stupid accuracy in favour of a theoretical framework that is testable and that has predictive power.

(Science is not alone in this.  Not even humans are alone in this.  Any creature that can learn to use tools will use a variation of the scientific method to develop an understanding of a tool in order to use it successfully.)

The steps of the scientific method, put roughly, are:

·         Informal observation

o   An apple falls to the ground

·         Systematic observation

o   Various fruit in the garden fall to the ground, as do leaves and twigs

·         Formulation of a generalised, falsifiable hypothesis

o   “Unless otherwise supported, an object will when released always approach the ground” – if we drop an object and it hangs in the air or rises, then this will prove the hypothesis to be incorrect

·         Testing of hypothesis

o   Systematic release of a variety of items

o   Each test constitutes evidence for or against the hypothesis

·         Falsification of hypothesis

o   A helium balloon when released floats up

o   If a falsifiable hypothesis cannot be shown to be false, it will eventually become a Theory

·         Modification of hypothesis

o   Based on the results of experimentation (evidence) the hypothesis may be either rejected as false or, if appropriate, modified

o   “Unless otherwise supported, an object that is heavier than air will when released always approach the ground”

Theories can serve as the basis for new hypotheses, with the example above, we could posit that objects with mass will accelerate towards each other in proportion to their combined mass divided by their separation.  This new hypothesis would be tested and refined until a Theory remains which is not falsified.  Any new Theory which has more predictive power and which explains a greater range of phenomena will replace lower level theories – as neopolitan’s basic theory of stuff dropping is replaced by Newton’s theory of gravitation which is then replaced by Einstein’s General Theory of Relativity.

This explanation of phenomena and the predictive power of a hypothesis are what are meant when scientists refer to “explanatory power”.

William Lane Craig continually refers to the explanatory power of the God Hypothesis – his whole “Cosmological Argument from Contingency” is predicated on the idea.  Here’s the argument again (from his debate with Lawrence Krauss):

  1. Everything that exists has an explanation of its existence (either in its own nature or in an external cause).
  2. If the universe has an explanation of its existence, that explanation is God.
  3. The universe exists.
  4. Therefore, the explanation of the universe is God.

Later in the debate, while summarising, Craig says:

… I explained that contingent beings are more probable given God’s existence than on atheism. Dr. Krauss will have to say that the existence of contingent beings is just as probable on atheism as it is on theism. But that seems incorrect because atheism has no explanation for the existence of contingent beings.

Note that by “contingent beings” here Craig means things that did not have to exist, but do.

Take a moment for Craig’s words to sink in.  If his words don’t seem silly to you, try reading them again.  Usually, a summarisation papers over the gaping holes in an argument but in this case, the summarisation make absolutely clear that Craig’s argument is incoherent.

First we need to decode the term “probable on” in reference to hypotheses.  If you do a Google search on this term, you will reach two types of uses:

·         a statement is evidence for an hypothesis if and only if the hypothesis is more probable on the statement than before (Florida Philosophical Review)

·         What about the first point of evidence that the existence of contingent beings is more probable on God’s existence than on atheism? (William Lane Craig)

The first usage here is the form you’ll be more likely to see, unless you restrict your search to apologetics sites (and sites critiquing apologetics sites).  It refers to the probability of a hypothesis being affected by the presentation of evidence.  Presumably, a statement is evidence against a hypothesis if and only if the hypothesis is less probable on (the basis of) the statement than before.

The second usage is the sort of misuse of logic that we’ve come to expect from Craig.  Let me rephrase him a little to take out the deceptions:

·         What about the first (point of evidence) argument that the evidence (existence of contingent beings) is more probable on the hypothesis H (God’s existence) than on the hypothesis H’ (atheism)

Can you see it?

I’ll tidy them both up and let you compare them on more even footing:

·         the hypothesis is more probable on the evidence (than another hypothesis) (FPR)

·         the evidence is more probable on the hypothesis (than another hypothesis) (WLC)

Okay, so Craig has it back to front.  No surprise there because he’s trying to defend a hypothesis rather than find a truth.

Looking at his statement again:

… I explained that contingent beings are more probable given God’s existence than on atheism. Dr. Krauss will have to say that the existence of contingent beings is just as probable on atheism as it is on theism. But that seems incorrect because atheism has no explanation for the existence of contingent beings.

and rewording:

·         X argued that:

o   the evidence is more probable on hypothesis H than on hypothesis H’

·         X states that Y must argue that:

o   the evidence is just as probable on hypothesis H’ as on hypothesis H
·         X believes that the argument that (according to X) Y must present is incorrect because
o    hypothesis H’ provides no explanation for the evidence

In other words, Craig is arguing that the probability of evidence is affected by the ability of a hypothesis to explain that evidence.

If you have ever been amazed by the way some theists simply dismiss good evidence against their position and unquestioningly accept any evidence in support, no matter how flimsy it may be, this might give you some clue as to why. 
I cannot explain this good evidence in light of my hypothesis that God exists, therefore I reject this good evidence. (There are no fossils!  Have you looked in a museum? … There are no fossils and no museums!) 
In the light of my hypothesis that God exists, this flimsy evidence is probable because even an idiot can explain it in terms of God, therefore I accept this flimsy evidence. (The Earth is perfectly designed for human habitation - so long as we ignore storms, earthquakes, droughts, solar radiation, disease, large infertile regions, depleted fish stocks, etc etc)



  1. Your post's initial link to "On Evidence" points to "file:///E:/my crap/link to On Evidence", which I'm sure only works on your computer. Would you fix that, please? Thanks!


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