Weighing a Chicken with a Yardstick

Author Greg Koukl Published on 04/24/2013

Can science disprove the existence of the soul? Here Greg deals with advances in computer science and neurology, and the limitations of science.

I received a letter from a listener last week. Some of you might remember the comment that I made about four or five weeks ago that it’s impossible for science to prove that there is no soul. This gentleman was a bit bothered because he felt I was speaking in a vacuum, as it were, and I really didn’t know what I was talking about, and making a comment like that not only misleads my listeners into having a false sense of confidence about this issue, but also to those who know better it makes me a little bit foolish.

Let me give you a couple of points that he made and then I’ll give you my response because I stand fully behind what I said earlier. He mentions that I made this comment that science would never be able to disprove the existence of the soul or the immaterial mind then he quotes Christian philosopher Mortimer Adler. Many of you have probably heard his name. He’s written some fine books. He says that Adler disagrees with me in a particular book that Adler wrote, Intellect: Mind Over Matter. “Adler investigates the body-mind problem from a Christian philosophical perspective. He prefers to call the soul or immaterial mind the intellect. And he agrees with people like J.P. Moreland that the brain is a necessary but insufficient condition to explain the mind.” In other words, the brain works together with the mind, but it’s something different than the mind. It has to be there for the mind to work. Although Moreland doesn’t say that entirely, he does say there’s a connection. But it is something different from the mind, which would be my view.

The writer goes on to say, “[Adler] goes on a step further and says that if science is ever able to produce a machine that can conceptualize on a conversational level it will prove that the brain is sufficient to explain the mind and therefore do away with the necessity of postulating an immaterial mind.” Adler doesn’t believe this is possible, but the way to disprove the existence of the mind and therefore undercut the Christian position is to produce a machine that can conceptualize on a conversational level. And if it can do that then it will do what we think it takes a mind to do. That would prove that a mind is not necessary and therefore, by inference, would prove that human minds don’t exist and Christianity would be discredited.

The writer notes that “Adler spends some time explaining why conceptualization is the premier attribute of the human mind and why the experiencing of emotion is of no consequence, not the attribute of self-awareness.” This is an important point. “The reason I’m writing this is because you made your grand pronouncement that science will never be able to disprove the soul without giving any indication that you are aware of the implications of quantum physics, or of the progress in artificial intelligence and the neurological sciences. Aside from the fact that the onus of proving a proposition is on the person who makes it [presumably me in this case], and certainly the existence of the soul is not proved, it appears contrary to your assertion that this is a metaphysical idea that at least theoretically can be disproved by science. Adler points out that Christians would probably not accept this proof and would go on as if nothing had happened. But he knows that the game would be up and Christianity would never again be what it was.”

He concludes his letter, “I hope you will [respond on the air] because this kind of statement in a vacuum, so to speak, convinces knowledgeable listeners that you haven’t a clue as to what you’re talking about, and of course this contradicts the very premise of your show. Lest you think I’m some kind of rabid physicalist, I am a Zen Buddhist with a great respect for the Christian religion even though I consider dualism to be a profound error.” And it’s signed “respectfully.”

I would like to take a few moments and hopefully convince you that I’m not speaking in a vacuum and that I do know what I’m talking about. But I also want to give you some tools of thinking to help put down this broad concern. The concern is that because of the progress of neurological sciences and computer technology and the idea of artificial intelligence (I’m going to set the quantum mechanics issue aside for today because it’s a separate issue) that we’re actually getting close to a machine that can actually think. Once we do that, once we make a machine that can actually think and, in Adler’s words “conceptualize on a conversational level,” then we will have proven away the existence of the soul. When the soul is gone, Christianity is gone and our position is ultimately refuted. My response is you don’t have to be frightened of that for a number of reasons.

First, my view that science is incapable of proving that souls don’t exist is hard to escape given the current definition of science. That definition is based on a materialistic view of the world called naturalism. Science deals with physical things governed by physical laws. According to this definition, when the writer started talking about non-physical things he’s talking about theology or philosophy, but he’s not talking about science. Modern science deals only with the physical universe of cause and effect, governed by natural laws in a metaphysically closed system. By very definition, science cannot address itself directly to the question of whether non-physical things like souls exist or not. Such a question is outside its capabilities, as science is now currently defined. Some other method is necessary.

It’s as if the scientist is attempting to say, “We don’t see invisible things; therefore invisible things aren’t there.” But one can’t see invisible things precisely because they’re invisible. Of course you wouldn’t be able to physically measure a non-physical thing. Science has a tendency of assuming something doesn’t exist because it can’t measure it. But this approach simply is circular and, therefore, false.

Philosopher Dr. Greg Bahnsen calls this the “Crackers in the Pantry Fallacy.” To answer the question “Are there crackers in the pantry?” one need only go look. But not everything is proven in the same way. This is a physicalist response; it tests the existence of physical things. But a soul by definition is not a physical thing, therefore you can’t “go look” for it in a physical kind of way.

This was my principle point in the comment quoted. He wrote “Contrary to your assertion, this is a metaphysical idea that, at least theoretically, can be disproved by science.” I disagree. Metaphysical arguments can’t be disproved by science, even theoretically, precisely because they’re meta-physical. They transcend the physical realm.

It’s like trying to weigh a chicken with a yardstick. Yardsticks don’t give weight; they give length. If you said your chicken weighed 27 inches, you’d be speaking nonsense. It’s called a category error. Yardsticks simply weren’t made to do that sort of thing. That’s my point. Science, strictly speaking, is not even capable of testing for souls, so how can it disprove the existence of souls? It can’t.

Now on to Mr. Adler’s thoughts, and let me quote the letter writer because the wording is important: “If science is ever able to produce a machine that can conceptualize on a conversational level it will prove that the physical brain is sufficient to explain the mind, and thereby do away with the necessity of postulating an immaterial mind.... The experiencing of emotion is of no consequence, nor even the attribute of self-awareness.”

First, when a dualist—one who believes there are two things that make a human being, a body and a soul—when a dualist speaks of the existence of a soul he means something much more than the ability to “conceptualize on a conversational level,” and any attempt to address the mind/body problem in this truncated fashion misses the mark wildly.

If the goal is to somehow prove that the brain and physical nervous system, etc., are fully capable of explaining what we believe the soul does, that the mind is really nothing more nor less than a physical brain, then he’s got to go the distance. His alternate model has to explain it all, not just one aspect.

To the contrary, the experiencing of emotion and the attribute of self-awareness is of tremendous consequence because these are both critical attributes of the mental life that require an explanation from the physicalist. These simply cannot be dismissed with a wave of the hand, nor can one dismiss other mental attributes. Does this machine hold beliefs about things? Does it have intentions and purposes? Does it freely will to do things? Does it feel pain or fear? Does it experience the taste of a strawberry or feel the frustration of unrequited sexual desire?

If this machine model of mind cannot actually do these things—not imitate them; a mere imitation won’t do—then it does not do what human minds do. And if it does not account for all of the details of the mental life of a human soul then it does not “do away with the necessity of postulating an immaterial mind.” On the contrary, when we look at all of the details and ask the question, “What view best explains the evidence?”, the idea of an immaterial mind does a better job of explaining the vast landscape of mental experience than does the machine-as-mind alternative.

Secondly, “if/then” assertions (“If science is ever able to produce a machine that can conceptualize on a conversational level, [then] it will prove that the physical brain is sufficient to explain the mind.”) can be true conditionals but still be meaningless in the face of a category fallacy. The conditional statement “If I was a trolley car, then I’d have wheels,” is true but useless; you’re not a trolley car and you’ll never be one, not even theoretically. Adler’s statement about machines and minds is much like the statement, “If I can show you an eighth note that’s colored blue, then I will have proven that musical notes have color.” That’s true enough, as far as it goes, but such a statement doesn’t change one whit the fact that musical notes are not colored things.

The same category fallacy applies to this issue of the mind. A moment’s reflection will demonstrate that mental states simply are not physical things. When we contemplate our own mental life, we are aware of thoughts, beliefs, sensations, yet we’re not the least bit tempted to believe they are the sorts of things that have weight, texture, size or extension into space.

My argument is that these are precisely the kinds of things machines can never do by very nature. Machines are material by nature; mental states are immaterial by nature. And no re-ordering of mechanical parts is going to make emotion and ideas and desires and thoughts pop into existence from machinery.

So first, science by its very nature can’t disprove a soul’s existence because science deals with the physical and is not equipped to measure the meta-physical.

Second, a conversation machine is not enough. One would have to create a machine that could actually do—not imitate-but actually do—everything a soul does.

Third, that will never happen because of a fundamental category fallacy: physical things accomplish physical effects, and the mind’s functions are not physical, therefore a physical machine will not be able to do what a mind does.

With all of that said, I’m going to give you the farm. I’ll concede, for the sake of argument, everything I’ve refuted up until now—I’ll say that science can deal with this, that a physical machine can actually produce non-physical things like thoughts and intentions, and that it could do every little thing that a human soul could do. What then? What would that prove about human souls? Absolutely nothing.

And this brings me to my final criticism of this reasoning. Even if I granted this fabulous machine, a machine that had every single characteristic of a human being’s mental life, if I granted the farm on this one, it would prove absolutely nothing regarding the existence of a human soul.

If a machine was invented that could conceptualize on a conversational level, a machine that could hold beliefs, have intentions and purposes, freely will to do things, feel pain and fear, experience the taste of a strawberry and feel sexual frustration, the only thing it would prove is that a machine could understand, feel, think, desire, and get horny. It proves something about machines; it proves nothing what-so-ever about humans.

It may prove that it’s possible for a machine to feel through its machinery what a human being already feels through his soul. But it would not prove that a human being is a mere machine. It would not prove that a human soul doesn’t exist.

Actually, it might prove another thing (and this I got from a Star Trek episode, though philosopher Richard Swinburne argues this way, too). If a machine can be made to do all the things a human can, it may prove not that men don’t have souls, but that machines do have souls. Once again, it would not prove that human souls don’t exist. In fact, it wouldn’t even speak to the issue.

This is a serious flaw and I’m a bit stunned that someone of Adler’s stature has made this mistake. To “prove that the physical brain is sufficient to explain the mind and thereby do away with the necessity of postulating an immaterial mind,” does not lead inexorably to “human minds don’t exist.”

This is simply a non-sequitur. The second does not follow from the first. To suggest that the shaking house (to use a timely illustration) could have been explained by a large truck driving by does not prove that the truck shook the house, not an earthquake. The suggestion merely identifies the range of possible explanations. Even if a thing is a possible explanation, it doesn’t follow that it’s a necessary explanation or even the best explanation. That’s an entirely different question. An alternate explanation, even a viable one, simply is not a refutation of the first position. And that’s Adler’s mistake.

As you can see, my prior statement was not made in a vacuum, as was suggested.