Argument By Analogy

An argument by analogy takes place when the arguer:

1. Has a point to prove about something
2. Gives you an analogy for the thing
3. Points out that the analog contains the feature they are trying to prove exists in the original
4. Concludes the feature in the analog must also exist in the original.

The flaw in this method of argument

The flaw is simple: the analogy always breaks down somewhere. If the analogy breaks down, the conclusion the arguer is trying to draw from the analogy just doesn’t follow. That’s all there is to it. Argument by analogy is rarely as good as an argument by logic, evidence or facts. Clearly if the arguer had any logic, evidence or facts to support his case he would present them. That he resorts to argument by analogy shows his argument is probably devoid of logic, evidence or facts.

Examples

The most persistent users of argument by analogy are ID creationists. For example, Michael Behe is especially fond of his Mount Rushmore analogy:

For example, unintelligent physical forces like plate tectonics and erosion seem quite sufficient to account for the origin of the Rocky Mountains. Yet they are not enough to explain Mount Rushmore.

Of course, we know who is responsible for Mount Rushmore, but even someone who had never heard of the monument could recognize it as designed.

So by analogy, life on Earth must also have been designed. He goes on to invoke William Paley and his watch analogy – essentially the same argument only with a watch instead of Mount Rushmore. The obvious place the analogy breaks down is that neither Mount Rushmore nor a watch can have offspring, while living things regularly  reproduce themselves. Since this reproduction (with minor changes) is fundamental to the theory of evolution, and since it obviously doesn’t work with Mount Rushmore, Behe’s analogy is bogus. The only startling thing in my view, is how ID proponents like Behe can still use this lame analogy when it is so obviously bogus and has been debunked so many times.

Michael Egnor (another creationist) uses argument from analogy in his plea for dualism - ‘Verizon Deniers’ Find a Cellphone. He compares the human mind to a cell phone, which (as we all know) picks up signals from elsewhere. That is, we know the people we hear on the phone don’t actually live inside the phone – the phone is just a receiver of the voices. Egnor concludes that the human brain is the same – the mind exists elsewhere (in some unspecified non-material realm), and the brain is just a receiver for the mind’s thoughts. Of course, we know that if we placed the cell phone in a faraday cage that is impervious to radio waves, the signal would be lost. That is one place the analogy breaks down, since there is no equivalent way to block the “signal” (analog or digital – ha ha), from the “mind” to the brain. We also know that damage to specific areas of the brain can produce specific changes in personality or other brain functions, while damage to specific areas of the phone produce no analogous changes in the message received. (Usually damage to the phone produces either no change or the phone stops working completely.) So right there we have two places the analogy breaks down, and we can dismiss the argument. It is notable that Egnor produces no actual evidence for this rather extraordinary claim of his. (Orac did a fine and more detailed take-down of Egnor’s argument, as did Steven Novella and others.)

Correct uses of analogies

I believe there are two correct uses of an analogy in a discussion. The first is to explain something that is complex and perhaps technical, in language that is simpler or within the recipient’s experience. As an example, I modestly (well no, not really) present the Beatles analogy I used in the Lost Tomb of Jesus post. James Cameron used the analogy of some future archaeologist finding a tomb in Liverpool, marked with the names John, Paul, George and Ringo, and concluding he had found the lost tomb of The Beatles. I wrote that, by analogy, Cameron had really found a tomb with the names John, Paul, George and Britney, and concluded Britney Spears was the drummer in The Beatles. (Bear with me – you have to read the whole post.) But my analogy wasn’t used to make the case – I had done that by examining the statistics and showing where they were wrong. The analogy was to help explain it.

The other correct use of an analogy is to get around a mental block – where someone simply can’t conceive of the point you are making so you make an analogy they might be able to think about. An example would be to explain to a theist, how an atheist simply has no belief in God. A religious person possibly couldn’t even conceive of there being no God, so instead you present Bertrand Russell’s teapot analogy. Here, he believer is asked to consider if he believes there is a teapot in orbit between the Earth and Mars, and when he realizes he can’t prove there isn’t one he might understand why the atheist has no belief in God and why the burden of proof is upon the person saying God (or a teapot in orbit), exists, rather than upon those saying they don’t. Note that the teapot analogy doesn’t prove the point, but it might help the theist understand the idea.

Comments

[Berlzebub]

I have a couple of trolls at my blog who are using my wife as an analogy for God. Not just her existance, but me being married to her. When I pointed out that I actually have evidence supporting my claim, the guy (Justin) has handwaved it away.

Yes, they drive me a little nuts, but it takes away some of the boredom, and gives my brain some exercise in finding the flaws to their *ahem* "reasoning".

Anyway, good post. I used Sagan's "invisible dragon in my garage" analogy, but Justin didn't seem to grasp the concept (not surprisingly).

[Lepht]

the teapot's a good one: it comes from Bertrand "T3h Aw3sum" Russell, and it's much less offensive to the fundies than the Invisible Pink Unicorn or the FSM. it's converted a few folks over here.

Lepht

[Jimmy_Blue]

Berlzebub:

We know Justin is a dimwitted lying asshat from what he posted in that thread over at Ryan's place, so don't be surprised if the obvious does escape him completely.

Skeptico:

It seems Egnor and Chopra share the same idea about the mind and brain, and even use a similar analogy to express it, Chopra uses the brain as a radio and the mind as a radio transmitter. I guess if great minds think alike there is no reason to suppose the stupid don't.

That latest thread of Chopra's that you linked to has some thoroughly crap analogies that Chopra's followers triumphantly wheel out only to have them explode in their face. In fact, analogies were all they had.

[eric]

The problem is the expression "reasoning by analogy."

Analogy is a great way to teach. It is a good way to open people up to ideas that don't intuitively resonate. You touched on this fact when you said "the analogy was to help explain it."

So, teaching by analogy can be the best approach.

And understanding by analogy is fine, too. Really abstract notions can be given more "body" in your head via analogy.

Keeping things on the topic of I.D, I'll give an example:

America's economy is like the world; it's a system. Now, in economics, we can look at the whole and be amazed that every business and every craftsman someone ends up with precisely the materials it/he needs, when he needs them. Indeed, the incredible complexity of the system boggles the mind.

There is just no way all of this precise meeting of needs occurred randomly. If it had, it wouldn't work so well. Surely, someone designed the economy.

The analogy here draws attention to the fact that when we look at complex systems, we see patterns. We see complexity and we see things interacting with an efficiency that, intuitively, feels very carefully crafted.

The analogy, one hopes, loosens the listener's attachment to his "gut sense" that "all this stuff must have been planned," by providing him a real world example of a similar system that we all intuitively know developed organically.

Which brings us back to the beginning. The problem is the term "reasoning" by analogy. Analogy doesn't do reasoning, it does analogy.

It's like saying "I'm reasoning via photography." It strips the word "reasoning" of its meaning.

[Bronze Dog]

Good comment, eric.

And yeah, I remember an analogy I thought was entertaining:

Evolution is like capitalism.
ID is like Communism.

[Daniel Hawkins]

Great post.

I agree that analogies can be useful when explaining difficult or technical topics, but I think that sometimes it is overused, and used too soon in teaching.

In physics or math it is often useful when trying to determine whether a statement is valid to think about the extreme cases. This often quickly shows whether or not the statement holds for all cases.

Because I have this habit, I often notice when analogies don't hold up as well as a professor would like, which is why I hate it when they begin the lecture with an analogy and spend the majority of the time elaborating on it. This may make the students feel good about themselves for being able to "understand" the concept, but when they have to do real problems or think about the concept in a new way, they are limited by the analogy they learned.

To me that is the biggest danger of analogies - they may hold for the point you are making, and indeed for most situations, but in new and unusual circumstances the breakdown of the analogy may be extremely subtle and lead you unwittingly to the wrong conclusion.