Saturday, May 30, 2009


Of Philosophers And Scientists

PZ Mxyzptlk has a post on Alvin Plantinga's evolutionary argument against naturalism, as summarized in an article at Christianity Today.

I think PZ underestimates the philosophical sophistication of the argument (which, of course, does not mean it is either correct or true). The Wikipedia article on the argument shows that there is a lot of nuance going on and, indeed, an entire collection of objections to the argument and Plantinga's responses has been published.

I won't pretend to have studied Plantinga's argument or the responses thereto beyond the Wikipedia article and a few expositions of it by Plantinga and other theists, so my thoughts on it are best described, charitably, as preliminary.

PZ states:

In Plantinga's world, if we queried the inhabitants with some simple question, such as, "Is fire hot?", 50% would say no, and 50% would say yes. This world must be populated entirely with philosophers of Plantinga's ilk, because I think that in reality they would have used experience and their senses to winnow out bad ideas, like that fire is cold, and you'd actually find nearly 100% giving the same, correct answer. Plantinga does not seem to believe in empiricism, either.

But that's not what Plantinga is on about. As he says in his article:

Of course you are more likely to achieve your goals, and of course you are more likely to survive and reproduce if your beliefs are mostly true. ...

... This means that the neurophysiology that caused or produced that behavior has also been adaptive: it has enabled them to survive and reproduce. But what about their beliefs? These beliefs have been produced or caused by that adaptive neurophysiology; fair enough. But that gives us no reason for supposing those beliefs true. So far as adaptiveness of their behavior goes, it doesn't matter whether those beliefs are true or false.

Plantinga here is not saying that nearly 100% of people wouldn't conclude that "sticking your hand in fire is a bad idea" -- that's adaptation -- or even that people wouldn't converge on a description of fire as "hot," rather than the term "cold" (used for another set of phenomena), he's saying that such adaptation does not guarantee that our "beliefs" about such things as why fire is hot (say, the existence of phlogiston) are correct. Furthermore, though Plantinga does not so state clearly (a point Wikipedia notes that Michael Ruse has made), his argument goes to beliefs that are not, themselves, empirically testable, such a philosophical naturalism/materialism. In the case of those kinds of beliefs, it is less obviously wrong to assign them a 50/50 probability of being, in fact, true.

It should be understood, as the Wikipedia article points out, that Plantinga is not arguing against the fact of evolution:

Plantinga states that he is not attacking the theory of evolution,[16] which only yields the self-contradiction when connected with philosophical naturalism but is not equally inconsistent with theism.

He is not even arguing that philosophical naturalism is wrong; only that holding to a belief in adaptive evolution renders also holding to a belief in philosophical naturalism not rational. I think there are a lot more holes in his arguments than Plantinga would like to admit but, as I said, I haven't studied it enough to spout off about it.

PZ does touch on a point that, in my opinion, renders the argument as a whole ... well ... academic:

He's reduced to a bogus either/or distinction. Either we are organic machines that evolved and our brains are therefore collections of random beliefs, or — and this is a leap I find unbelievable — Jesus gave us reliable minds.

I don't think that's quite what Plantinga is saying. From his article:

The problem, as several thinkers (C. S. Lewis, for example) have seen, is that naturalism, or evolutionary naturalism, seems to lead to a deep and pervasive skepticism. 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. ...

Clearly this doubt arises for naturalists or atheists, but not for those who believe in God. That is because if God has created us in his image, then even if he fashioned us by some evolutionary means, he would presumably want us to resemble him in being able to know; but then most of what we believe might be true even if our minds have developed from those of the lower animals.

What he is saying is that, given the premises of philosophical naturalists/evolutionists and the premises of theists, theists do not have a logical objection to the conclusion that their minds are reliable enough to deliver truth about these higher-order assertions about the world, while naturalists do. It seems to me that Plantinga is performing a bit of philosophical sleight-of-hand here, arguing at two different levels of the logic involved. On the evolutionary account as stated by Plantinga (large caveats there), maybe it is not rational for naturalists to believe that philosophical naturalism is also true. But on a evolutionary account it is equally irrational to believe that theistic belief is true and theists are in exactly the same boat as naturalists are. Plantinga wants to keep the evolutionary argument when discussing theism (denying he is questioning it) but doesn't apply it to theism. Simply saying that theists assert the premise that a god exists doesn't render their account rational (though it might be formally logical) if there are no grounds to believe the premise is true.

Remove the evolutionary account for both beliefs and the argument dissolves into the traditional theist/atheist brawl and ya pays yer money and takes yer choice.

One last point (which is what got me to write anything at all on this): PZ mocks Plantinga for being innumerate:

(First, an amusing aside: footnote [7] is an acknowledgment of the assistance of someone else in doing those calculations. He needed help from an expert to multiply simple probabilities? Does being a philosopher mean you're incapable of tapping buttons on a calculator?)

There was also a fairly well-known 19th Century naturalist who had a similar problem:

Caerleon, North Wales, June 19, 1869.

I am much obliged to your Correspondent1 of June 5 for having pointed out a great error in my 'Origin of Species,' on the possible rate of increase of the elephant. I inquired from the late Dr. Falconer with respect to the age of breeding, &c., and understated the data obtained from him, with the intention, vain as it has proved, of not exaggerating the result. Finding that the calculation was difficult, I applied to a good arithmetician; but he did not know any formula by which a result could easily be obtained; and he now informs me that I then applied to some Cambridge mathematician. Who this was I cannot remember, and therefore cannot find out how the error arose. From the many familiar instances of rapid geometrical increase, I confess that, if the answer had been thirty or sixty million elephants, I should not have felt much surprise; but I ought not to have relied so implicitly on my mathematical friend. I have misled your Correspondent by using language which implies that the elephant produces a pair of young at each birth; but the calculation by this assumption is rendered easier and the result but little different. A friend has extended your Correspondent's calculation to a further period of years. Commencing with a pair of elephants, at the age of thirty, and assuming that they would in each generation survive ten years after the last period of breeding—namely, when ninety years old—there would be, after a period of 750 to 760 years (instead of after 500 years, as I stated in 'The Origin of Species'), considerably more than fifteen million elephants alive, namely, 18,803,080. At the next succeeding period of 780 to 790 years there would be alive no less than 34,584,256 elephants.


Just because some of us need help with math is no reason to assume we're stupid.


I posted my usual observation about arguments which are supposedly about evolution being often more appropriately arguments about reproduction and/or development.

Of course, there are so many responses on PZ's blog that it is impossible to follow what is going on.

I wasn't aware that there was a Wikipedia article on this particular argument. (No surprise, though.) I'll have to look at this article before proceeding. Thanks for this pointer.

Tom S.
The Wikipedia article is a mess. I've tried to sort through some of the replies and counter-replies that have been published, and have come to the conclusion that the whole issue is little more than a "sophisticated" game. Plantinga starts with the assumption that there's no reason to assume that evolution would produce "true beliefs". Everything else proceeds from that assumption. The problem is that there's absolutely no reason to assume that evolution would fail to produce true beliefs. More importantly, there's no reason to assume that "belief" is a single trait, but if you don't make that assumption, Plantinga's argument falls flat.

The rest of his argument is a set of "You're wrong, so I must be right" nonsense, worthy of an all too clever 12-year-old. Or, as Douglas Adams puts it, "man goes on to prove that black is white, and gets killed at the next zebra crossing" (rough paraphrase, from 20-year-old memory). To begin with, his argument says that the probability of "true belief", given evolution, is either low, or it's impossible to tell. But he ignores the "impossible to tell". Even worse, his argument assumes a high probability for "traditional theism". Now, I consider myself a Christian, but I believe that any rational person could consider the idea of god and religion as anything other than a highly improbable idea. That's why people make arguments based on faith...most of them are pretty loopy too, granted. Even Paul admits that what he's saying is pretty outrageous. It's just mind boggling that these people discuss the merits of Plantinga's arguments as if they were serious ideas. It like reading "baraminology" wonder how people can say things like that with a straight face.
There are a number of what I consider to be fatal objections to Plantinga's argument. Here's just one: he assumes that there's simply an arbitrary relation between adaptive behavior and true belief. So adaptive behavior may be correlated with true beliefs, and it may not be.

His reasoning seems to be that since we have no a priori reason to believe that there's a necessary connection between adaptive behavior and true belief, we're not justified in assigning any non-arbitrary relationship between the two.
I agree that the Wikipedia article is not worth much on its own, except as a vague pointer to the arguments that are being made against Plantinga.

Plantinga is, I think, hiding a lot of sins in that claim that "the probability that our minds are reliable under a conjunction of philosophical naturalism and evolution is low or inscrutable.
From Plantinga's article:

"The problem, as several thinkers (C. S. Lewis, for example) have seen, is that naturalism, or evolutionary naturalism, seems to lead to a deep and pervasive skepticism. 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. ..."

And I threw in my usual response, which is that critters whose "cognitive or belief-producing faculties" produce unreliable representations of (relevant aspects of) the world end up as lunch for critters whose faculties produce more reliable representations. Natural selection in action.

Of course, that ignores the question of Truth-with-a-capital-T, but that's not my concern: philosophers are welcome to their armchairing about it.

And I'm not at all convinced that Plantinga's imaginary world full of people with systematically false beliefs could exist. To the extent that beliefs are both false and have causal efficacy on behavior, they'll be weeded and pruned so that they more and more reliably represent the world -- will be better and better approximations to being "true." Incomplete, yes. Inaccurate and unreliable sometimes? Sure. But unless Plantinga thinks the body of 21st century scientific theory is no better a representation of the world than was 10th century superstition, he has to allow that our representations, honed in the selective environment of science, are more 'true' now than they were then. Truth in this sense is a scalar quantity. As Isaac Asimov wrote
"[W]hen people thought the earth was flat, they were wrong. When people thought the earth was spherical, they were wrong. But if you think that thinking the earth is spherical is just as wrong as thinking the earth is flat, then your view is wronger than both of them put together."

--Isaac Asimov (1989). "The Relativity of Wrong." The Skeptical Inquirer, 14(1), 35-44. Fall 1989.
One other note. You (John) wrote:

"There was also a fairly well-known 19th Century naturalist who had a similar problem:"

Except that Darwin didn't make a probability estimate the core of his argument. Plantinga does.
Quite true and, if you read Branden Fitelson's and Elliott Sober's article I just linked to, you'll see that it is a Bayesian probability argument that is not simple to formulate, though the math itself is not hard.
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