15.4: Looking for Alternative Explanations

Mass hallucination is in some ways like mass hypnotism. The hypnotist can place spectacular ideas into your mind, because hypnotism is a matter of suggestion. Mass hypnotism is the key to the famous Indian rope trick, say several magicians. The trick is performed by an Indian magician, called a "fakir." After showing a rope to his audience, he throws it into the air, where it stays vertically suspended. A boy, the fakir's assistant, climbs the rope and then disappears at the top. Several magicians who have analyzed the trick claim that the Indian fakir hypnotizes all the members of the audience into believing they have seen the trick, even though they haven't.

This is a fascinating but implausible explanation. Mass hypnotism is too difficult to pull off. It may not be as difficult to create as a mass hallucination, but it is right up there in implausibility.

There is, instead, a better alternative explanation. If a thin, strong wire were strung between two trees above the fakir, he could disguise a hook in the rope and toss the rope so that it hooks the wire and hangs suspended. The fakir's assistant could then climb the rope even though the rope looks to everyone in the audience as if it is unsuspended. Behind a puff of smoke, the boy could scramble along the wire and hide in the tree.

Exercise \(\PageIndex{1}\)

The wire and hook explanation is better than the mass hallucination alternative because

a. if it were correct, the trick would be less expensive.
b. mass hallucination is logically impossible.
c. it is too difficult to create a mass hallucination.
d. mass hypnotism requires accepting Eastern mysticism.

Answer

Answer (c).

To further explore the intricacies of finding the best explanation for a phenomenon when alternative explanations need to be considered, suppose you receive a letter asking you to invest your money with Grover Hallford and Associates (GHA), a new stock brokerage firm. You do have a little extra cash¹, so you don't immediately shut the idea out of your mind. The new stock brokers charge the same rates as other major brokers who offer investment advice. GHA is unusual, though, in that it promises to dramatically increase your investment because, according to the letter, it has discovered a special analytic technique for predicting the behavior of the stock market. Normally you would have to pay for any stock advice from a broker, but to show good faith, the GHA letter offers a free prediction for you. It predicts that the price of IBM stock will close lower next Tuesday from where it closed at the end of trading on the previous day, Monday. You place the letter in file 13, the circular file. However, the following week you happen to notice that IBM stock did perform as predicted. Hmmm. What is going on?

A few days later you receive a second letter from GHA. It says that GHA is sorry you have not yet become a client, but, to once again show its good faith, the company asks you to consider its prediction that Standard Oil of New Jersey stock will close up next Tuesday from where it was at the end of Monday. Again you decline to let GHA invest your savings, but you do keep an eye on the stock price of Standard Oil of New Jersey during the next week. Surprisingly, the prediction turns out to be correct. A few days later you receive a third letter suggesting that you invest with GHA, containing yet another free stock tip, but warning that there is a limit to how much free advice you will receive. Are you now ready to invest with GHA? If not, how many more letters would you have to receive before you became convinced that the brokers truly do understand the logic of the stock market? If you demand thirty letters, aren't you being foolish and passing up the chance of a lifetime? Surely GHA is on to something, isn't it? Other brokers cannot perform this well for you. How often do you get a chance to make money so easily? Isn't GHA's unknown technique causing them to be able to make correct predictions? And even if GHA is cheating and somehow manipulating the market, you can still take advantage of this and make money, too. Think about what you would do if you were faced with this decision about investing.

You may not have been able to find a reasonable alternative explanation to GHA's claim that it understands the causal forces shaping the stock market. Many people cannot. That's why the swindle works so well. However, it is a swindle, and it is illegal. What GHA did is to get a long mailing list and divide it in half. For their first letter, half of the people get a letter with the prediction that IBM stock will close higher next Tuesday; the other half get a letter making the opposite prediction—that IBM will not close higher. Having no ability to predict the stock market, GHA merely waits until next Tuesday to find out who received a letter with the correct prediction. Only that half then gets a second letter. Half of the second letters say Standard Oil of New Jersey stock will go up; the other half say it won't. After two mailings, GHA will have been right two times in a row with one-fourth of the people it started with. The list of names in the lucky fourth is divided in half and GHA generates a new letter. Each new mailing cuts down by 50 percent the number of people GHA has given good advice to, but if the company starts with a long enough list, a few people will get many letters with correct predictions. You are among those few. This explains why you have received the letters. Along the way, many people will have sent their hard-earned money to GHA, money that will never be returned. This swindle is quite effective. Watch out for it. And don't use it yourself on anybody else.

Once again we draw a familiar moral. The degree of belief you should give to a claim that A causes B (that GHA's insight into the stock market causes its correct predictions) is improved or lessened depending on whether you can be more or less sure that reasonable alternative explanations can be ruled out. Thinking up these alternatives is crucial to logical reasoning. Without this creativity you can be more easily led away from the truth, that is, conned.

Exercise \(\PageIndex{1}\)

Back in the nineteenth century, a manuscript was discovered in a large, sealed bottle underground in London. The tightly rolled manuscript was signed "Brother Bartholomew,'' who was known to have been a famous prophet of the fifteenth and sixteenth centuries. The manuscript contained several remarkable statements. Unlike the vague predictions in the sixteenth-century writings of Nostradamus, this manuscript made precise predictions. It described in some detail how to build a steam engine, a repeating rifle, and a telegraph. The manuscript didn't contain the English names for these inventions, just the plans. It also said that a new country would someday be formed far to the west of London and that its first leader would be named "Woshen-tun." The manuscript contained the date "1523" on its cover page. A reliable chemical analysis of the ink on the cover page established it as a kind of ink commonly used during the sixteenth century.

Assuming that this fictitious story is true, what is the best comment to make about whether the evidence shows Brother Bartholomew to have been a successful prophet?

a. wouldn't put a whole lot of faith in this claim. Making a decision about Brother Bartholomew from just one source of evidence is tough; if two manuscripts were found, it would be twice as good evidence though. So, it is about 25 percent likely he was a prophet.
b. Everything Brother Bartholomew says came true, so he was foretelling the future. Also, the chemical tests that were done on the manuscript show with high probability that it was written back in 1523.
c. I can't believe this shows he is a prophet, since the manuscript doesn't predict anything that wasn't already known at the time of its discovery.
d. I can't believe in the authenticity of the document because London did not exist in 1523.
e. There is no proof that the document was not foretelling the future.

Answer

(e) is true, but the answer is (c). Predicting a repeating rifle in the nineteenth century is not predicting something unexpected, because the rifle was already invented by then. Yet a good test requires predicting an unexpected event. So (c) is the right answer. Notice that there were no predictions of x-rays, lasers, genetic engineering, computer games, or the AIDS epidemic. If the document had predicted something new for a time after it was discovered, then it would be a stronger piece of evidence in favor of Bartholomew's prophetic powers. Because it did not, there is a mundane and more plausible alternative explanation that hasn't been ruled out—namely, that the document is a forgery created in the nineteenth century using a sixteenthcentury cover page.

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¹ Some textbook authors make some fantastic assumptions, don't they?