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November 20th, 2009 (Permalink)


Q: I am a medical student with a very random and growing interest in fallacies and paradoxes. I have spent much time looking for recommendations on your website (among others) for a book (textbook or otherwise) that covers most, if not all, formal and informal fallacies. Do you know of any such books that would cover the fallacies in a manner similar to what you have done on the taxonomy portion of your website? Or are there any other books you would recommend?―Michelle Taylor

A: There is no book that uses a taxonomy, as far as I know―and I know pretty far. Of course, every logician since Aristotle who has written anything much on the subject has classified fallacies in some fashion, but these systems of classification are comparatively "flat", and lack the tree-like structure of the taxonomy. Instead, fallacies are usually classified in a few broad categories, such as "fallacies of relevance", "linguistic fallacies", "fallacies of presumption", etc.

Most books that cover a large number of fallacies tend to restrict themselves to informal fallacies, and formal fallacies are often only dealt with in passing in books on formal logic. Many introductory logic textbooks will cover both types of fallacy, but usually only about a dozen to two dozen informal fallacies. Moreover, the informal fallacies covered in textbooks are the "usual suspects", that is, the traditional logical fallacies many of which go back to Aristotle: begging the question, ad hominem, straw man, etc. You probably won't find any of the fallacies discovered in recent decades by psychologists―such as the base rate fallacy, the conjunction fallacy, and the hot hand fallacy―or those studied by statisticians―such as the regression fallacy, the Texas sharpshooter fallacy, and the multiple comparisons fallacy.

That said, there are many fine textbooks from which you can learn not only much about fallacies, but also the positive principles of logic. Formal fallacies, in particular, can only be fully understood within the context of the system of formal logic in which they occur; for instance, to fully appreciate syllogistic fallacies requires an understanding of the formal system of categorical syllogisms.

The closest thing to a single book that meets your criteria is Madsen Pirie's The Book of the Fallacy, which is out of print, hard to find, and expensive when found. Pirie's more recent book How to Win Every Argument: The Use and Abuse of Logic appears to be an expanded version of his earlier work, so I think that it is safe to recommend even though I haven't read it yet.

November 15th, 2009 (Permalink)

The Puzzle of the Terrorist Acquaintance

The Agency for Counter-Terrorism (ACT) comes to you with a logical problem. The agency has information on four subjects, one of whom is known to be a terrorist. To protect the innocent, we will refer to them as Subjects 1 through 4.

Subject 1 is the known terrorist. Subject 1 is acquainted with Subject 2. Subject 2 has met Subject 3, therefore they are acquainted. Subject 3 was observed talking to Subject 4, so they're also acquainted. Subject 4 is known not to be a terrorist. It's not known whether Subjects 2 and 3 are terrorists or not.

ACT wants to know: among the four subjects, is a terrorist acquainted with a non-terrorist? Choose an answer:

  1. Yes.
  2. No.
  3. There is not enough information to determine whether a terrorist and a non-terrorist are acquainted.


Acknowledgment: Thanks to Vasilios Magriplis for pointing out a typographical error in the original wording of the puzzle that has now been corrected.

November 11th, 2009 (Permalink)

Are you intelligent but irrational?

Test yourself with an article in the latest issue of Scientific American Mind on the difference between intelligence and rationality by psychologist Keith Stanovich. It contains a number of puzzles that may make you feel foolish, but don't feel too bad if you get a wrong answer: you're in good company. Regular readers of The Fallacy Files should recognize the Wason selection task and a puzzle based on the base rate fallacy, and I hope would not be fooled by them.

I've known a lot of highly intelligent people, including some much smarter than I am. However, some of them were perplexingly irrational, at least about some things. I used to be very puzzled by this, until I drew a distinction between intelligence/stupidity on one hand, and wisdom/foolishness on the other. It's perfectly possible to be an intelligent fool: I've known a few! It may even be possible to be a wise idiot, though I've never actually met one. However, the point is that raw intelligence and rationality don't always go hand-in-hand. Intelligence is innate, but rationality must be cultivated.

The article is based on Stanovich's book What Intelligence Tests Miss: The Psychology of Rational Thought, which I would love to receive a review copy of.

Source: Keith E. Stanovich, "Rational and Irrational Thought: The Thinking That IQ Tests Miss", Scientific American Mind, 11/2009

November 8th, 2009 (Permalink)

New Books: Denialism and Unscientific America

Continuing the twin themes of "where's the harm?" and weird science, here's a couple of new books: Chris Mooney and Sheril Kirshenbaum's Unscientific America and Michael Specter's Denialism. Both appear to deal with the widespread scientific illiteracy that helps lead to the harm that I've noted in previous entries. For instance, the quantum quackery practiced by James Arthur Ray is made possible by the fact that so many people have no idea what quantum mechanics is all about, and can't tell the difference between the real thing and bafflegab. You don't have to be a physicist to be able to tell that Rhonda Byrne doesn't know what she's talking about; you just need to be scientifically literate. I haven't done a book club in a long time, and it's possible that one or both of these books might make good material. As always, it would be nice if someone would send me review copies.


Weird Science
November 6th, 2009 (Permalink)

Where's the Harm?

November 1st, 2009 (Permalink)

What's New?

The Multiple Comparisons Fallacy. I haven't added it to the Taxonomy yet; that is to come. As usual, if you notice any errors or omissions, please let me know.

Solution to the Puzzle of the Terrorist Acquaintance: Yes, a terrorist is acquainted with a non-terrorist. To see this, consider Subject 3. Either Subject 3 is a terrorist or not. Suppose that Subject 3 is a terrorist; then a terrorist is acquainted with a non-terrorist, since Subject 3 is acquainted with Subject 4. What if Subject 3 is not a terrorist? Then consider Subject 2, who is also either a terrorist or not. If Subject 2 is a terrorist, then a terrorist is acquainted with a non-terrorist, since Subject 2 is acquainted with Subject 3. So, suppose that Subject 2 is not a terrorist; then a terrorist is acquainted with a non-terrorist, since Subject 1 is acquainted with Subject 2.

Another way to solve the puzzle would be to consider all the possibilities for Subjects 2 and 3: they're both terrorists, neither is a terrorist, Subject 2 is a terrorist but Subject 3 is not, and Subject 2 is not a terrorist but Subject 3 is. In each of these possibilities, a terrorist is acquainted with a non-terrorist.

If you read the article discussed in the previous entry, you may have noticed that this puzzle is a variant of the first puzzle given in the article. I wondered what would happen if there were four people rather than three; specifically, I wondered whether it would still be solvable. As you can see, it is. Of course, I also changed the relation between the characters from looking to being acquainted, and the property of being married to being a terrorist.

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