conclusion was true, intelligent design could be regarded as scientific, thereby destroying a barrier between evolution on the one hand and creationist areas of knowledge, science, and theology on the other.
7. The rationalistic fallacy: believing that rational arguments will persuade—or, the assumption that human beings will govern their affairs on a purely rational basis by using only logical trains of reasoning. This is a common error, especially among professors; this book may be an excellent example of it! Rational arguments may not persuade if they are difficult to follow or if they challenge long-held and cherished beliefs.
8. Reductio ad absurdum (Latin for “reduced to an absurdity”): reducing an argument to the point of making it appear absurd. Reductio ad absurdum makes use of the law of non-contradiction, which says that a particular statement “A” cannot be both false and true at the same time. Of course, the demonstration of absurdity may rely on a very extreme example of the principle being discussed—so extreme that it is an unfair distortion of the statement given. (See fallacy 9, “Straw man,” below.) The wording of the statement is very important, particularly when you use statements like “A is always true” or “B can never occur.” A single counterexample can show your position to be absurd. Mark Twain made use of the reductio ad absurdum principle when he wrote that many years ago the Mississippi River was “upwards of one million three hundred thousand miles long.” (See chapter 2, section E: “Mark Twain and Science.” ) Twain is illustrating the absurdity of assuming that the rate at which the Mississippi River is seen to shorten today has remained constant over millions of years.
9. Straw man: representing an opponent's view in a form so extreme that it is absurd. It suggests that your opponent's logic must be bad when the only thing that is proven is that the argument does not hold in the extreme. For example, your opponent gets his answer by dividing by a very small number. You then declare him wrong because, if you divide by zero, which is very small indeed, the answer is undefined. (See fallacy 8, “Reductio ad absurdum,” above.) Demonstrating a contradiction in an argument is valid, but not if you distort the argument into a case it was never intended to cover.
10. The tautological fallacy: formulating a conclusion that is true for whatever set of values (true or false) are entered into our table. The terms are defined in such a way that the conclusion cannot be disproved. Examples of tautologies are “the law of the excluded middle” (A or not-A), “de Morgan's law” (if not both A and B, then either not-A or not-B), and “proof by cases” (if at least one of A or B is true, and each implies C, then C is also true). Tautologies are not always fallacious. The tautological fallacy occurs when the conclusion is already contained in the premises—perhaps using slightly different words. The logical argument does not advance us beyond what is already known or assumed.
11. Miscellaneous fallacies. Either or both premise lines may not be true, and even the conclusion line may not be true. If the first two premise lines are true, then the conclusion line should be true and will be as long as the argument is valid. For example, recall the syllogism at the beginning of section B, “Deduction versus Induction,” above:
| Premise 1: | Fido is a dog. | |
| Premise 2: | Dogs eat meat. | |
| Conclusion: | Fido eats meat. |
This syllogism is sound. But what of the case where the third line instead reads “Bears eat meat”?
| Premise 1: | Fido is a dog. | |
| Premise 2: | Dogs eat meat. | |
| Conclusion: | Bears eat meat. |
The argument is not valid even though the conclusion is true. The third line introduces a forbidden fourth term (“bears”), and hence this case is also called the four-term fallacy. This represents an interesting case in that both premises and the conclusion (“Bears eat meat”) are true even though the logic—the argument—is not valid. Although the formula is true in terms of logic, it was just a coincidence that bears actually do eat meat; it didn't necessarily follow from the premises. To see that the conclusion does not actually flow from the premises, consider another syllogism with the four-term fallacy:
| Premise 1: | Polly is a bird. | |
| Premise 2: | Birds have feathers. | |
| Conclusion: | Bears have feathers. |
The logical structure is similar, but in this case you can see that the conclusion is absurd.
E. RHETORICAL DEVICES
Rhetorical devices use various phrases and tones for their effect, with or without regard to logic. “What is the authority for…?” is a rhetorical question that implies that, after considerable search, no such authority will be found. All of the fallacies, if they are used despite the user's knowing they are fallacies, are then rhetorical devices. Note the famous phrase “That's a rhetorical question,” meaning that you aren't supposed to answer the question, which was posed only for effect. Loaded words are another, and very common, rhetorical device.
1. Ad hominem: attacking the speaker rather than the speaker's argument. It is rather in the spirit of “If you have no good arguments on the basis of the facts, then you should: (1) cause confusion; (2) shout louder; (3) assert your opponent's ignorance of the issue; (4) accuse her of unethical or immoral acts; (5) ridicule your opponent; and so forth. Some recent examples include the following:
a. The astronomer Fred Hoyle has hypothesized that life may not originally have begun on Earth, but began somewhere else and then migrated to our planet (by various interesting ways). Daniel Dennett observes, in his book Darwin's Dangerous Idea (1995, pp. 314, 318), that skeptics sometimes refer to this idea as “Hoyle's Howler” as a way of insulting Hoyle by implying that he is stupid.
b. “The fact that a distinguished philosopher overlooks simple logical problems that are easily seen by chemists suggest that a sabbatical visit to a biochemistry laboratory might be in order” (Behe 1996, p. 221; Behe is a creationist). This sarcastic remark is also insulting.
c. “I have encountered this blunder so often in public debates that I have given it a nickname: ‘Berra's Blunder’” (Johnson 1997, p. 63). This is in the same category as the howler. Phillip Johnson was referring here to Tim Berra's use of the changing automobile design in the Corvette sports car to illustrate the concept of “descent with modification.” (See chapter 2, section G.1, “Automobile evolution.”)
d. “…creationist canards (lies) [regarding thermodynamics]…” and “…these thermodynamics howlers…” written by Paul R. Gross (an evolutionist) in his review of a book edited by Matt Young and Taner Edis entitled Why Intelligent Design Fails: A Scientific Critique of the New Creationism.
Note that these examples of attacking the person rather than the scientific claims as exemplified are used by both creationists and evolutionists (two each of the four examples). It is reprehensible whichever side does it.
2. Ad ignorantiam: using the ignorance of one's opponent as evidence of the correctness of one's own position. (See rhetorical device i, “ad hominem,” above.)
3. Loaded words. “We all have naturalism in our bones and even conversion [to Catholicism] does not at once work the infection out of our system.” (Citing of C. S. Lewis by Dembski; emphasis mine.) Infection is an excellent example of a loaded word, as is easily demonstrated by replacing infection with a neutral word. For example: “We all have naturalism in our bones and even conversion [to Catholicism] does not at once work our prior beliefs out of our system.” (The difference between the two statements is emphasized in the italicized words.)
