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The neuroscience fallacy and the startling truth

July 28, 2012 2 comments

I want to draw your attention to something I think is quite important to think about, in regards to causality and its relation to the scientific enterprise. More particularly, I am concerned about a particular application of the scientific enterprise to how the modern world conceives of human thought, of the brain and of consciousness. My belief is this: the scientific project, when it comes to the brain, does not understand causality–in fact it routinely commits a very basic logical fallacy.

Quite a claim, you might say. I mean, science is supposed to be the discipline that makes sense out of the world. If anyone should understand causality, it is the scientists! I feel as I write this that I am perhaps making an obvious blunder. Yet, for the life of me, I cannot see what that blunder is. I spend much of my time immersed in logic, dealing with the world of mathematical abstractions, and I think that I’ve gotten pretty good at logic, as a result. And then I look around me and I see science using this very same logic, to deduce causality, in a way that seems to me to be completely backwards.

Let me explain what I mean. Probably the most basic concept in logic is that of a syllogism: A implies B. A syllogism is an “if, then” statement. It looks nice to write a syllogism with a little arrow:

A \rightarrow B

This helps us visualize the direction of the logic. We use syllogisms all the time! Here are some examples.

1. If it was raining, then I would have used my umbrella.

2. If the Yankees win the world series this year, I will shave my head.

3. If you don’t eat your meat first, you can’t have any pudding.

Forget the fact that none of these statements are actually true in general. The point of these is examples are not their truth or falsehood, but their form. Now, for any syllogism, there is another simple syllogism that is logically equivalent to it. Logically equivalent means that the two statements imply each other–if you know one, you know the other. The syllogism that is logically equivalent to a given syllogism is called its contrapositive: NOT B implies NOT A. In symbols, it is usually written something like this:

\neg B \rightarrow \neg A

Thus the little symbol “\neg” stands for “not.” Here are, in words, the contrapositives of the above statements:

1. If I do not use my umbrella, then it was not raining.

2. If I do not shave my head after the world series this year, the yankees did not win the world series this year.

3. If you can have some pudding, then you ate your meat.

The equivalence of a statement and its contrapositive are self-evident logical truths.

A common logical fallacy, on the other hand, is to assume a syllogism is equivalent to its converse: B implies A. This is often called “affirming the consequent.” For example, just because I use my umbrella doesn’t mean it had to be raining. I could have used it, for example, to block the sun. Intuitively, we can see that statements are not equivalent to their converses because, as a rule, the same event can be brought about by different causes. For example, I might frequently use my umbrella to block out the sun as well, demonstrating that the converse of statement 1 is false.

Now, bear with me here, because things are about to get a little tricky. Often the fallacy of affirming the consequent occurs because one considers the contrapositive of the converse instead. The fallacy is believing that “A implies B” entails that “NOT A implies NOT B.” Since the logical implication “goes in the same direction,” it is easy to make this mistake.

Now, I believe that modern scientific thinking often ignores this basic logical fact in the way that it approaches its understanding of causality. Further, I think that it has ignored it because it has a materialistic bias, and thus the consequences for accepting it are startling and at odds with the philosophical presuppositions of modern scientific thinking.

It is especially clear to me that the project of neuroscience falls victim to this logical fallacy. Neuroscience, or at least the popular interpretation of it (and, I suspect, the internal beliefs of most neuroscientists in regards to what they think they are accomplishing) is practically built upon making this error.

Consider first an example. Scientists do a study, and find:

1. The removal of physical circumstances A results in the disappearance of mental state/experience/event B.

Then they conclude:

2. Therefore physical circumstances A cause mental state/experience/event B.

If we consider this as a syllogism, it is clearly the logical fallacy I described above.

For example, scientists may discover that feelings of depression and unhappiness are associated with lower levels of serotonin in the brain (I haven’t verified this, by the way–I might have the science part wrong here). By correcting this imbalance, the scientists are able to remove the feelings of depression. Now, I hope no one misunderstands me here. I believe that this sort of thing, if done responsibly, is very good. But I think that we misunderstand what is going on here, tragically, in a way that undermines our understanding of the human soul.

Many people, upon hearing that we now have a pill that cures depression by altering a chemical state of affairs in the brain, will conclude that this state of affairs causes the mental condition known as depression. They will say things like “my emotions are nothing more than a chemical state of affairs.” And the scientists their will support them in this conclusion. The logic, however, actually ought to go in the other direction: if removal of the serotonin imbalance also removes the depression, then the contrapositive of this causal relationship, the only statement that logically follows from this experimental result, is that depression is the cause of the serotonin imbalance.

This conclusion, however, is unacceptable to modern neuroscientists, because their entire project is to reduce mental states to physical states. The reason they do this is, well, because they are afraid that not doing so would be unscientific. If they would accept that there is something like “mind” that is metaphysically distinct from “brain” and interacts dynamically with it, then the whole project of science, as they understand it, is undermined.

In a way they are right. But they need to get over it! We would do well to stop thinking about science as a special sacred realm of knowledge, as a special epistemological project. We need to get back to thinking about all things carefully and logically. We have reified science far too much, and this hinders our understanding of many things. But that’s a topic for another post…

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