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Tom Ames

Posts: 238
Joined: Dec. 2002

I just read a fascinating analysis of the structure of ID's probability argument [Sober, E. (2002), "Intelligent design and probability reasoning." Int. J. Phil. Rel. 52:65-80].

In his paper, Sober argues that the ID movement relies upon a probabilistic analog of modus tollens. Modus tollens is a deductively valid argument of the form:
If X then Y
~Y
-------------
(therefore) ~X

The relevant probabilistic analog of this would be the argument: "if a theory X says that Y is improbable, and we observe Y, then we should conclude that the theory is probably false." (This is not deductively valid.) ID makes this into an argument against naturalistic evolution by arguing that some feature (the vertebrate eye, or "irreducible complexity" in general) is improbable under naturalistic laws, and that therefore those laws can be rejected as the sole mechanism for generating that feature.

Sober describes why observing a low probability event does not necessarily provide evidence against the corresponding theory. One example he gives is taken from Richard Royall's wonderful book Statistical Evidence -- A Likelihood Paradigm. Suppose you are brought an urn, and you want to test the hypothesis that it contains 2% white balls. Is drawing a white ball evidence against this hypothesis? If you know that there exist two urns, one containing 2% white balls and the other containing 0.0001% white balls, drawing a white ball is actually evidence in favor of the hypothesis that the urn contains 2% white balls!

This example highlights the need to discuss evidence in comparative terms. You observe an event (such as the existence of the vertebrate eye) that has a low probability under theory X. But it is crucial to know the probability that that event would occur under theory Y as well, if one is to distinguish between them.

How probable is the vertebrate eye or the bacterial flagellum under ID? We do not know. Furthermore, there is a concerted attempt by the ID movement to avoid any committment that would allow such a probability to be calculated, even in principle.

I highly recommend this paper to anyone who finds the probabilistic arguments of the ID movement as annoying as I do. Sober does an admirable job of undercutting the basis of Dembski and Behe's major claims.

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-Tom Ames

Dr.GH

Posts: 2324
Joined: May 2002

Welcome, and thanks for the reference.

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"Science is the horse that pulls the cart of philosophy."

L. Susskind, 2004 "SMOLIN VS. SUSSKIND: THE ANTHROPIC PRINCIPLE"

Tom Ames

Posts: 238
Joined: Dec. 2002

I'd like to quote Sober's concluding paragraph in it entirety:
 Quote My critique of the intelligent design movement has been based on the comparative principle I stated about evidence -- to say whether an observation counts as evidence against evolutionary theory and in favor of the hypothesis of intelligent design, one must know what each predicts about the observation. I have challenged intelligent design theorists to produce a theory that has implications about the detailed examples of "irreducible complexity" that Behe describes. However, there is another response that intelligent design theorists might contemplate. This is to deny the comparative principle itself. Dembski has seized the horn of this dilemma. If he succeeds in developing an epistemology of this sort (so far he has not), the way will be paved for an unprecedented result in the history of science -- the rejection of a logically consistent theory that confers probabilities on observations, but does not entail them, and its replacement by another, without its needing to be said what the replacing theory predicts.

Apropos of Sober's conclusion, I'd even more highly recommend Royall's Statistical Evidence -- a book that Dembski cites but shows little eveidence of having understood.

Paticularly revealing in this regard is Dembski's response to an earlier critique by Sober, Fitelson et al., in which he justifies his strict reliance on non-comparative (i.e., Fisherian) modes for the evaluation of evidence by pointing out the prevelance of this approach in applied statistics.

This is about as weak an argument as could possibly be made: "scientists prefer Fisher, therefore my argument is correct." Significance testing has dominated the statistical landscape primarily because it has been computationally easy relative to other approaches. Furthermore, the statistical landscape is changing: in many fields (medicine, ecology, computational biology) explicitly Bayesian approaches are being developed and routinely applied.

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-Tom Ames

ExYECer

Posts: 36
Joined: May 2002

I have been using Sober's paper and others to argue against Dembski on ISCID. For those interested, the paper can be found Online

More interesting papers by Sober

Dembski, not surprisingly, comments on Sober and on the use of Bayesian statistics

Detecting Design? A First Response to Elliott Sober William A. Dembski

Fitelson's page

Sobel on Modus tollens

 Quote 20William Dembski would eliminate, in the light of Fine-Tuning, the particular chance-hypothesis Chance, notmerely by the small probability for Fine-Tuning conditional on Chance, but by that together with the fact that Fine-Tuning is ‘specified’. I explain in (Sobel forthcoming-b) why I recommend that his way of eliminating chancehypotheses, whatever exactly that way is, not be tried at home.

Review by Sobel of The Design Inference: Eliminating Chance Through Small Probabilities,

A devastating review imho although a bit 'telegraph style'

Edited by ExYECer on Jan. 05 2003,15:27

Tom Ames

Posts: 238
Joined: Dec. 2002

Thanks, ExYECer, for the additional resources. I hadn't seen any of Sobel's work.

Also, I'll look for your ISCID contributions.

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-Tom Ames

Dr.GH

Posts: 2324
Joined: May 2002

Odd.  All the Dembski critiques by Sobel seem to have been taken off line.

Edited by Dr.GH on Nov. 30 2003,21:40

--------------
"Science is the horse that pulls the cart of philosophy."

L. Susskind, 2004 "SMOLIN VS. SUSSKIND: THE ANTHROPIC PRINCIPLE"

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