The Three Failures of Creationism. Walter Fitch
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implies C (conclusion). There are many forms of errors in the use of syllogisms, and some of the more common errors are examined at the end of this section.
B. DEDUCTION VERSUS INDUCTION
If one sees that whenever an event happens it is always followed by the same second event, one may come to believe that the first event causes the second one. For example, “Every time I push this button, the doorbell rings. Therefore the pushing of the button is the cause of the doorbell ringing.” This is inductive logic. One infers a general rule on the basis of a limited (but generally large) number of observations. However, there is nothing about an induction that guarantees that it will be a correct conclusion. For example, using precisely the same logic, one gets “Every morning just before dawn the cock crows and then the sun rises. Therefore, the cock's crowing causes the sun to rise.”
Alternatively, one may conclude (deduce) a particular thing from a general rule. For example, “Dogs eat meat, so I deduce that my Fido eats meat, too.” The understood but unstated premise is that Fido is a dog.
| Premise 1: | Fido is a dog. | |
| Premise 2: | Dogs eat meat. | |
| Conclusion: | Fido eats meat. |
The conclusion of a valid deduction must be true if the premises are true, whereas an induction may be correct but is not proven. The conclusion of a valid deduction is usually of narrower meaning but true, whereas an induction is usually of broader meaning but unproven (although perhaps likely to be true).
The two most commonly used logical forms are deduction and induction. Consider now a series of items that are either logical errors or rhetorical devices designed to convince you, the reader or listener, of something. You need not memorize the names of all these logically related processes, but just recognize them when they occur. It is good practice, if what you are reading feels slippery, to try to find out why you feel that way. You will frequently discover malpractice in word usage. Several such abuses are illustrated here. Writers rarely provide you with a syllogism, or even a partial one, so you must figure it all out for yourself.
C. ANALOGICAL REASONING
Analogical reasoning is the process of making your logic, in a difficult case, exactly like your logic in another case that the listener will readily understand. The point is generally to make the understanding of your logic easier. For example, “If it is not immoral for tigers to eat humans, then it is not immoral for humans to eat humans.” The analogical form changes only one word here and invites you, should you believe the first proposition, to accept the second statement as logically equivalent. Most of us would disavow the conclusion, illustrating that analogy does not lead to something having been proved. Its value lies in making it easier to understand the meaning or content of an argument. Darwin said in The Origin of Species, “Analogy may be a deceitful guide” (1859, pp. 454—55). Nevertheless, Darwin's first chapter is a long list of analogies arguing that if natural variation is available for the breeder of organisms, variation must be present for natural selection to act upon as well.
Analogies can be humorous, as in, “If practice makes perfect, then mal-practice makes mal-perfect.” This clearly demonstrates that analogies may make an argument clearer but cannot provide support for an argument.
D. LOGICAL FALLACIES
1. Begging the question (circularity): assuming the conclusion you wish to reach.
A circular argument does not advance our knowledge beyond what was already known or assumed in the premises. That is, the argument being presented begs us to ask the question, What is the support for the premises? Or, What do the premises have to do with the conclusion? Consider the following syllogism:
| Premise 1: | Complex things can be produced only by a designer. | |
| Premise 2: | The human eye is a complex thing. Conclusion: | |
| Conclusion: | The eye must have been designed. |
Are we sure of the first premise? Is it really true that the only way a complex thing can come into being is by the work of a conscious designer?
Or consider how begging the question may be used in political speech:
| Premise 1: | Smith is a good family man. | |
| Premise 2: | Smith was a great football player. | |
| Conclusion: | Smith will make a good mayor. |
We must ask what the premises have to do with the conclusion. Unless you feel that being a good family man or a great football player somehow builds your character or prepares you for political office, the premises have nothing to do with the conclusion.
2. The equivocation fallacy (also called a category error): using a word with two different meanings in the same argument.
Examples of the equivocation fallacy are given below. A particularly obvious example is the following. First read down the left half of the syllogism to get the silly conclusion that is clearly wrong.
| silly | correct | ||
| Premise 1: | I am a nobody. | I am a person of no importance. | |
| Premise 2: | Nobody is perfect. | There is no individual that is perfect. | |
| Conclusion: | I am perfect. | (No logical conclusion possible.) |
Now read the syllogism again utilizing the phrasings on the right for the word nobody. This shows how changing the meaning of the term nobody between premises 1 and 2 renders the conclusion silly, although the syllogism on the left side is formally valid.
The usage of this equivocation fallacy is the basis of the creationist's rather insidious declaration that evolution is not a fact. One meaning of the word theory, found in ordinary, everyday usage, is that of a guess. Creationists often say in a disparaging tone that evolution is only a theory, meaning that it is only a guess and not a fact. But when a scientist uses the term theory, the scientist means a well-supported explanation uniquely consistent with many thousands of observations. Consider, for example, Newton's theory of motion, Copernicus's heliocentric theory (that the Earth rotates around the sun), Einstein's theory of relativity, or atomic theory.
The creationist's syllogism goes like this:
| Premise 1: | Evolution is a theory. | |
| Premise 2: | A theory is only a guess. | |
| Conclusion: | Therefore the theory of evolution is only a guess (and thus is not a fact). |
This argument is invalid because it uses different meanings of the word theory. Its illogical result arises from changing the meaning of the word theory between premise 1 (“a well-substantiated scientific truth”) and premise 2 (“a guess”). This has also been called the four-term fallacy because of the two different meanings of theory. The correct syllogism is:
| Premise 1: | Evolution is a theory. | |
| Premise 2: | A theory is a well-supported explanation of many observations. | |
| Conclusion: | Therefore, evolution is a well-supported explanation of many observations. |
This form of the argument is valid and the premises are true, so the conclusion is true. It is puzzling that creationists continue to assert that evolution is “only a guess.”
A third instructive example of the equivocation fallacy is the following:
| Premise 1: | Humans are a species. | |
| Premise 2: | A species is a mental construct. | |
| Conclusion: | Humans are a mental construct. |
The concept of a species is a mental construct, a creation of the human mind, but that is different from human beings being a species. To make a valid argument, the statements should be as follows:
| Premise 1: | Humans are interfertile with other humans. (That is, they can interbreed.) | |
| Premise 2: | A group of interfertile individuals is termed a species. | |
| Conclusion: | Humans are a group called a species. |