In this sections, we'll consider a number of fallacies, i.e., common errors in reasoning which people (even well educated, careful people) often fail to notice in their own arguments or which devious people might use in their arguments in the hope that we won't notice them.
The practice of identifying and classifying fallacies has been a popular one since Aristotle's time. Here, we'll consider a relatively small group of commonly discussed fallacies, most of which are likely to rear their heads again later on in this course. If you're curious about other fallacies, there are some pages about them on the web. See, for instance, Charles Ess' page on fallacies.
What follows then is a collection of bad arguments. In most cases, you'll quickly see they're bad arguments, but what you should think about is exactly what it is that makes them bad arguments. Each of these arguments can be seen as an example of a particular type of fallacy. When you've thought for a bit about why the argument is a bad one, click on the text that says "What's wrong with this argument?" and you'll get a description of the fallacy involved.
Something to keep in mind: There may be more than one way of saying what's wrong with each argument, so you shouldn't necessarily worry if you come up with a different answer than I did (although it would be a good idea to run your answer by me). You should, however, make sure you understand the explanation that's given of what's wrong with the argument (and so of the type of fallacy the argument involves).
What's Wrong With These Arguments?
1. If you came to every class then you passed the course. But you did not come to every class, therefore you did not pass the course.[What's Wrong With This Argument?]2. If you came to every class then you passed the course. As a matter of fact, you did pass the course, therefore you must have come to every class.[What's Wrong With This Argument?]3. As scientists have shown us, the world is a well regulated place. They have discovered many laws of physics (such as the law of mass conservation). But everyone knows that you cannot have laws without a lawmaker. There must therefore be a Supreme Lawmaker. In spite of their anti-religious tendencies, then, scientists have actually helped to prove the existence of God.[What's wrong with this argument?]4. Students must decide whether they will have fun or do well. This student has decided to have fun, so I guess he won't be doing well.[What's wrong with this argument?]5. Everything in the Bible must be true. The Bible says it is the word of God and God would never lie.[What's wrong with this argument?]
6. If this doctor isn't punished for helping his patient to commit suicide, we send doctors the message that they can engage in euthanasia without fear of prosecution. If that happens, cases of euthanasia will become common. Thus, the public and the medical profession will become used to the idea of taking human life. Physicians will lose their natural reluctance to put patients out of their misery. Soon, assisted suicide will become commonplace, just another lifestyle choice.Here's What's Wrong With The Arguments:[What's Wrong With This Argument?]7. Successful people usually have large vocabularies. It seems then that having a large vocabulary must make one likely to be successful.[What's Wrong With This Argument?]8. Some people argue that capital punishment is necessary, because it is the only appropriate punishment for those who commit the most atrocious and depraved crimes. However, we should not pay attention to such arguments. It is well established that those who argue for capital punishment are usually people who see themselves as helpless and inadequate in a changing complex world. Subconsciously, such people see capital punishment as a way of striking back at a confusing world.[What's Wrong With This Argument?]9. People who think abortion should be banned have no respect for the rights of women. They treat them as nothing but baby-making machines. That's wrong. Women must have the right to choose.[What's Wrong With This Argument?]
P1: If you came to every class, you passed the course.
P2: It is not the case that you came to every class.
C: It is not the case that you passed the course.This argument commits the fallacy of denying the antecedent. Notice that premise 1 does not say that the only way to pass the course is to come to every class. The argument does nothing to rule out the possibility that a person who, despite skipping some classes, gets 90% on every test, assignment and exam will pass the course.
In general, any argument that has the form:
P1: If P then Q.commits the fallacy of denying the antecedent.
P2: It is not the case that P.
C: It is not the case that Q.
[Back to the list of arguments]
2. If you came to every class
then you passed the course. As a matter of fact, you did pass the
course, therefore you must have come to every class.
In general, any argument that has the form:
For more on the fallacies of affirming the consequent & denying the antecedent see 'The AB47 Example'.
3. As scientists have shown us, the
world is a well regulated place. They have discovered many laws of physics
(such as the law of mass conservation). But everyone knows that you cannot
have laws without a lawmaker. There must therefore be a Supreme Lawmaker.
In spite of their anti-religious tendencies, then, scientists have actually
helped to prove the existence of God.
This argument commits the fallacy of equivocation. In the second sentence, law means something like 'natural regularity'. In the third sentence, it means something like 'a command made by a governing body or person'. As long as we give the word 'law' the right definition in each premise, the premises are certainly acceptable. However, the arguer acts as though 'law' means the same thing in both sentences. Now, if it did, the argument would be valid, so there's a good strategic reason why the arguer would pretend that law means the same thing in each premise. The problem, however, is that if we try to use the same definition of 'law' in both premises, we no longer have a good reason to think both premises are true. In order to fool us, what the arguer needs to do is have us think 'law' means a different thing in each sentence when we're thinking about whether the premises are true, but not when we're thinking about whether the argument is valid.In general, a person commits the fallacy of equivocation, when a word or phrase in her argument has more than one distinct meaning and her argument relies on this, but she is disguising the fact that this is so (or at least fails to realize this).
[Back to the list of arguments]
4. Students must decide whether they
will have fun or do well. This student has decided to have fun, so I guess
he won't be doing well.
But surely P1 misrepresents the alternatives. Why can't a person do both? When you misrepresent the alternatives in this way, you commit the fallacy of false dichotomy. In general, the fallacy of false dichotomy occurs when an argument presents a set of alternatives as though they are exclusive or exhaustive (or both) when in fact they are not.
Exclusive Alternatives: alternatives are exclusive when they are such that if one holds the other cannot, e.g., being square and being circular are exclusive alternatives. Notice that argument #2 presents doing well and having fun as exclusive alternatives although they are not.
Exhaustive Alternatives: alternatives are exhaustive when
they cover all the possibilities, e.g., being pregnant or not being pregnant.
5. Everything in the Bible must be true.
The Bible says it is the word of God and God would never lie.
In general, an argument begs the question when it implicitly
or explicitly assumes the truth of whatever it is supposed to be proving,
i.e., when it engages in circular reasoning.
is deductively valid. So, when does an argument of this sort commit the slippery slope fallacy? When one of the following two problems exists:
1. Weak Links: The chain of reasons may have a weak link. You need to be very careful when stringing together a series of claims with the form 'If X happens, then Y will happen'. If one of those claims turns out to be false, then the argument fails to be convincing. [One way of thinking about why this is so is to note that in a slippery slope argument none of the premises work independently. They stand or fall together.]
2. Magnifying Uncertainty: If your argument
has the form:
If an argument runs into trouble on either of these counts, it commits the slippery slope fallacy.
7. Successful people usually have large vocabularies.
It seems then that having a large vocabulary must make one likely to be
successful.
Here is another example of a casual fallacy:
Here, while it is true that there is a correlation between the rooster crowing and the sun rising it is clearly a mistake to think that the rooster crowing causes the sun to rise. This particular sort of fallacy is so common that it has its own name. The rooster has committed the post hoc fallacy, i.e., the fallacy of assuming that since event A always precedes event B, event A must cause event B.
8. Some people argue that capital punishment is necessary, because it is the only appropriate punishment for those who commit the most atrocious and depraved crimes. However, we should not pay attention to such arguments. It is well established that those who argue for capital punishment are usually people who see themselves as helpless and inadequate in a changing complex world. Subconsciously, such people see capital punishment as a way of striking back at a confusing world.
9. People who think abortion should be banned
have no respect for the rights of women. They treat them as nothing but
baby-making machines. That's wrong. Women must have the right to choose.