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August 19, 2008


It seems to me that this argument works only if you can demonstrate that under materialism, our beliefs can have no influence over our behavior. Because if they CAN, and if there is an advantage to having true beliefs rather than false beliefs, then evolution would favour minds that produced true beliefs over minds that produced false beliefs.

J.P. Moreland and C.S. Lewis both argued that under materialism, the mind can have no causal influence over the brain at all. If Plantinga argued something like that, then I think his argument would be sound.

Hey Sam,

I hear what you're saying, but, it does miss the point of what Lewis and Plantiga are arguing. The issue is not whether or not "true" or "false" ideas are advantageous. The issue is: if our thoughts are merely the product of the cause-and-effect nexus of materialism, then those thoughts are NOT TRUE OR FALSE; they simply exist as effects from some cause. Lewis makes this point well: that for us to claim something is "true" and something is "false," then are we appealing to an authority that is outside of our sense of right and wrong. We actually believe that there is an objective thing called "right" and "wrong" that we are invoking.

So, if materialism is true, then these words (i.e., "true" and "false") are meaningless. Rather, we should just describe all thoughts like, "beneficial to the species" or "conducive to survival." But, in no way can they be "true" or "false" if they are merely the effects from some cause.

But, if they really do teach us about reality--that there really is something beyond us to which we appeal for right and wrong, then there really are "true" thoughts and "false" thoughts. But, then, as Lewis argues, materialism fails.

You can't have it both ways: You can't say that my thoughts are true or false, and then argue: yeah, but, your thoughts are just part of a neutral universe that is causing things all the time. That is self-refuting, since THAT thought you just had was just part of the natural universe. Hitler and Mother Theresa both had constant thoughts and both must be morally equal.

Pax Deo,

Hey Sam,

It doesn't come out in this snippet of Plantinga's but Plantinga does consider the view that beliefs do influence behavior. He argues that if beliefs influence behavior, then the evolutionary naturalist should think that the probability that evolution selected reliable cognitive faculties is still either low or inscrutable. After all, there are many ways in which false beliefs can yield adaptive behavior. For instance, say that Bob the Caveman finds himself face to face with a tiger. Now consider this desire-belief pair: Bob desires to be eaten by the tiger, but (falsely) believes that the best way to be eaten by the tiger is to keep away from it at all costs. This is a false belief that turns out to be very adaptive. It is easy to think of many more such examples, which is why Plantinga doesn't think it's probable that true belief would be selected by naturalistic evolution even if beliefs _do_ influence behavior.

I read the full article that Melinda linked to, and Plantinga does argue that true beliefs have no advantage over false beliefs in promoting survival, and that only behavior matters. Since advantageous behavior can result from false beliefs just as easily from true, evolution cannot be rationally affirmed if we assume materialism. That's a valid argument, I think, but I'm skeptical of the view that if materialism is true and evolution is true, that evolution would not be anymore likely to produce reliable cognitive faculties than unreliable cognitive faculties. The tiger analogies does show that it's possible for a false belief to produce advantageous behavior, but it doesn't show that false beliefs in general are just as advantageous as true beliefs.

David, I think you are confusing Plantinga's argument and Lewis' argument. They are similar, but they are not the same argument.

Hey Sam,

I spoke about "true" and "false" beliefs because those are the words you used in your comment.

You're right; I mentioned Lewis and Plantiga together only because Plantiga references Lewis. After doing that, Plantiga (above) says:

It leads to the conclusion that our cognitive or belief-producing faculties—memory, perception, logical insight, etc.—are unreliable and cannot be trusted to produce a preponderance of true beliefs over false....

This is not Lewis, per se, since Lewis does not say "preponderance," but that NO thoughts can be considered "true" or "false" since those words assume something outside of cause and effect exists.

Pax Christi,

I'd appreciate a little clarification from DavidP, please.

So is it fair to say that *if* words like "true" and "false" *assume* something outside of cause and effect, that trueness or falseness is so, independant of the viewers opinion? In other words, to claim trueness is to make a statement about something and if it is indeed true, the viewer has only judged correctly--they didn't make it any more the true by calling it true. Then it might follow that the trueness or falseness of any claim would assume that a standard setter was behind the scenes giving these words meaning. If not, trueness or falseness are only subjective words and really meaningless if their origins[thus value] were in/from the being who is making the judgement.

Is this what you understand Lewis to mean, or do I miss the point?

Brad B

There are many errors in Plantingas/Lewis/Repperts reasoning. I guess that proves minds are not reliable and naturalism+evolution is true.

"There are many errors in Plantingas/Lewis/Repperts reasoning."

Please share.

Today, Sunday Aug. 23, Greg quoted a distinguished professor of genetics at Harvard writing in the New York Times Review of Books that materialism is chosen as a conclusion by scientists even when the evidence points in the opposite direction towards the supernatural. I find the quote very enlightening and would like the whole quote and the reference if you wouldn't mind.
As Greg says, they are loading the deck.

Brian, here's the reference:

Richard Lewontin, 1997. Billions and billions of demons, The New York Review, p. 31, 9 January 1997 (review of Carl Sagan's The Demon-Haunted World: Science as a Candle in the Dark).

You can read the full quote here.

Plantingas seems to be making the distinction between evolution and naturalism as being: evolution is a scientific theory; naturalism being a philosophical point of veiw. Is this correct, or am I missing something?

Hey Brian B.,

Sorry, I haven't checked this post in a long time. I didn't know people would still read it!

The answer to your question is, "yes." What you have said is precisely one facet of Lewis' argument. When we use words like "true" and "false" we are really pointing to something that is True and False. If not, then those words don't mean anything more than, "that's not conducive to my survival" or "that's what I would not prefer," or whatever.

Now, Lewis was NOT arguing that because of this deduction (people use true and false as a means of appealing to something outside of our experience), it follows that there is a God/god. Rather, it means there is something truly "objective"--beyond human experience alone--to which we are appealing.

Now, for Lewis, it was a short step to say that the most probable next step is to assume that this Law of Morality comes from a Law Giver, or God.

Makes sense to me.
Read his Mere Christianity (first few chapters) and his Miracles.

Pax Christi,
David P.

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