Logic is defined as the science of evaluating arguments. This may be a little misleading because of the specific use of the word argument. In philosophy, argument does not simply mean disagreement. If you were to say that Ford produces better cars than Toyota and I were to say that Toyota produces better cars than Ford we would be disagreeing but not necessarily arguing. An argument must contain two elements. First, there must be the main point that is being argued for. This is called the conclusion. Arguments are sometimes confused with opinions because the conclusion of many arguments is an opinion. However, arguments are more than opinions because they contain a second element; the premises. In an argument, facts must be presented to support the conclusion and these facts are the premises. So now it should be clear why the example above is not an argument. While you may state that Ford produces better cars than Toyota in order for this to be an argument you must present reasons why Ford produces better cars than Toyota.
So we've established that arguments contain two parts. The purpose of the premises is to provide support for the conclusion. This support can be provided in two ways giving rise to two types of arguments. In deductive arguments, the premises support the conclusion as a matter of necessity. Another way of thinking about this is that if the premises in a good deductive argument are true, then the conclusion must also be true. On the other hand, in inductive arguments the premises support the conclusion as a matter of probability. So, in a good inductive argument, if the premises are true the conclusion will probably be true.
This distinction becomes very important when we begin evaluating arguments. If an argument is, in fact, inductive (as most arguments in philosophy are) then saying that the premises do not necessarily support the conclusion will be an unfair criticism. After all, the intent of inductive arguments is only to provide probable support. This may cause you to ask whether inductive arguments aren't always inferior to deductive arguments. This may be one way of thinking about it. However, there are many kinds of arguments that cannot be deductive. For example, if we want to make predictions or use statistical reasoning in an argument, we are arguing inductively. The very nature of some arguments is inductive. While we may wish it to be otherwise, there's little that can be done about this. We have to evaluate arguments within their proper context. This goes for all arguments and, as we'll see, is an important point to keep in mind when we consider various philosophical arguments.
Another important consideration with respect to evaluating arguments is the notion of proof. Throughout the semester we will be looking at various philosophical arguments which purport to prove a certain conclusion; for example, the existence of God. People often misunderstand the concept of proof by thinking that proving something demonstrates conclusively that something must be true. While this may be the case for deductive arguments, as we've seen it cannot be that way for inductive arguments. Since most philosophical (and scientific) arguments are inductive, it is impossible to conclusively prove the conclusion of these arguments true. That is, we will not be able to preclude evidence that may arise in the future to count against our conclusion. This being the case, proofs in philosophy tend to be attempts to find the most probable conclusion that fits the available evidence.
Still, no good system of reasoning would be complete without a foundation and in logic this foundation consists of three laws of thought. In essence, these laws represent the fundamental principles from which all our reasoning proceeds. They are considered self-evident which means that merely understanding them should be enough to recognize their truth. Because of their self-evident nature they can be used to deduce other important philosophical principles. Before considering these principles (and while we're still on the subject of proof) we should recognize that these laws of thought cannot, themselves, be proven. As Aristotle pointed out in his Metaphysics with reference to one of these laws: "some, indeed demand to have the law proved, but this is because they lack education; for it shows lack of education not to know of what we should require proof and of what we should not. For it is quite impossible that everything should have a proof; the process would go on to infinity, so that even so there would be no proof."
Before concluding our remarks on logic, we need to consider some common mistakes in reasoning; what we call fallacies. We should attend to these for two reasons. First, we want to be able to identify these mistakes if they occur in the philosophical arguments we will be analyzing. In fact, identifying fallacies may come in handy when considering non-philosophical arguments as well. Second, we should familiarize ourselves with fallacies to avoid committing them ourselves.
Aristotle originally identified many of these fallacies and later philosophers added to the list. There are many of these that can occur in everyday argumentation but here are the more common ones to watch out for in Bioethics.
1. Ad Hominem: a. attack the person (ad hominem abusive) b. question the person's motives for making the argument (ad hominem circumstantial) c. accuse the person of hypocrisy (tu quoque)
In these fallacies the arguer attacks the person instead of attacking the person's argument. It is often very difficult to keep these two separate. Does the following seem like a good argument?
Bill Gilmore has argued for increased funding for the disabled. But nobody should listen to that argument. Gilmore is a slob who cheats on his wife, beats his kids, and never pays his bills on time.
In fact, it is not a good argument because instead of criticizing Gilmore's argument for funding the disabled the criticism is about Gilmore himself. In fact, it is irrelevant to his argument whether or not he cheats on his wife, etc. While these may be reprehensible things, they do not necessarily mean his argument for increased funding for the disabled is a bad argument.
2. Ad Populum: the line of reasoning here is: "Accept the conclusion of my argument because everyone else does."
The problem with this argument is that the mere fact that everyone else believes something (or does something) is not a sufficient reason for you to accept the conclusion of your argument.
3. False Appeal to authority: While appeals to authority can be effective arguments, there are several points to consider:
Is the source an authority on the subject at issue? Is the source biased? Is the accuracy of the source's observations questionable? Is the source known to be generally unreliable? Has the source been quoted? Can the source's claim be settled by an appeal to expert opinion? Is the claim highly improbable on its face?
4. Ad Ignorantiam: Imagine I began my argument with the admission that I have no evidence. Then, I attempt to draw a conclusion from this lack of evidence. Sound like a good line of reasoning? Probably not. That's what happens in arguments which commit the Ad Ignorantiam (appeal to ignorance) fallacy. The fallacy has the form: no one has proven this therefore we can conclude something about this. Another way to think about this is that the arguer is claiming that since no one has proven the claim false, it must be true (or vice versa, since no one has proven the claim true, it must be false). But in every case the problem stems from the lack of evidence. In general, it is fallacious to conclude anything based on a lack of evidence. It's like saying "I've never tried beets before, but I know I won't like them." How do you know if you have no evidence?
I said this line of reasoning is fallacious in general, because there are a couple of important exceptions to this fallacy. Consider this argument: Teams of researchers have been searching for life on Venus for years and have failed to find any evidence of such life. So we may conclude that there is no life on Venus.
This is, in fact, a good argument, even though it sounds like an appeal to ignorance. The difference is the "team of researchers." If qualified researchers are searching for evidence this means they are probably qualified to find it and if they fail to do so this lack of evidence itself may be important. Therefore, we can draw a conclusion from it. This doesn't guarantee that the conclusion is true but no strong argument can guarantee that.
The second exception is connected with the presumption of innocence made in our legal system. The text has good examples of that under the appeal to ignorance fallacy so I won't duplicate that material here except to mention the exception.
5. Tu Quoque: Under Ad Hominem. Here's an example of the fallacy:
Dr. Morrison has argued that smoking is responsible for the majority of health problems in this country and that every smoker who has even the slightest concern for his or her health should quit. Unfortunately, however, we must consign Dr. Morrison's argument to the trash bin. Only yesterday I saw none other than Dr. Morrison himself smoking a cigar.
Yes, this does make Dr. Morrison a hypocrite. But, the question is does it make his argument against smoking a bad argument? No. While it would be better if he practiced what he preached the fact that he doesn't does not mean that what he is preaching is wrong.
6. Hasty Generalization: this fallacy occurs when you attempt to draw a conclusion about a whole group based on a few members of that group. Of course, not all generalizations are hasty but many which use very few individuals to make the generalization are. Like these examples from our first exam:
Anthony Davis, who goes to the local Mormon church, was arrested for car theft. Also, Kay White, who attends a different Mormon church was arrested for embezzlement. Clearly, Mormons are just a bunch of lawbreakers.
James got married a year ago, and today he is unhappy. Diane got married two years ago, and today, she too is unhappy. Apparently marriage no longer brings happiness to people.
In each of these arguments too few individuals are used to draw such general conclusions. This fallacious line of reasoning is the basis for many stereotypes. However, small samples do not always lead to fallacious conclusions. Our text has a good example of this which goes something like:
Substance Z was fed to four mice and within two minutes all four mice died. Therefore, substance Z is probably fatal to the average mouse.
This is a generalization, but a strong one. It is very likely, given the conditions, that the conclusion follows from the truth of the premise, even with such a small sample size.
7. Biased Statistics: Sometimes this fallacy is covered under the Hasty Generalization heading. A common mistake in statistics is using a sample which is too small to draw any conclusions from. In good statistical reasoning the sample is random, representative, and large enough from which to draw useful conclusions.
8. Bifurcation: Sometimes called false dichotomy is a fallacy that relates to disjunctive syllogisms. These arguments are valid but unsound because the either/or premise (the dichotomy) is false. This is a fallacy of presumption because the false either/or statement presumes that there are only two options. For example, Either I get into law school or my life is over. This would be an example of a false either/or statement. This fallacy can be committed even if the dichotomy is all that is stated in the argument. Usually, it is obvious what conclusion should be drawn so often the argument is not completely stated. Some of the examples in the text are not completed but let's consider one that is:
Either you let me attend the Dixie Chicks concert or I'll be miserable for the rest of my life. I know you don't want me to be miserable for the rest of my life, so it follows that you'll let me attend the concert.
The problem here is with the either/or statement. Surely, there's at least one other option! Remember though that not all dichotomies are false.
9. Begging the question: occurs in two ways. First, it can occur when you leave out a questionable premise in your argument, a premise that is required for the argument to work. For example, Given that murder is immoral it follows that abortion is immoral. Now, regardless of your view on abortion it should be obvious that there's a premise missing from this argument: Abortion is a form of murder. Without addressing this premise the argument is really not addressing the central issue. Another way of thinking about this is to say that the argument is not answering the central question involved; in other words, it's begging the question.
A second way this fallacy is committed is by arguing in a circle by having the conclusion of your argument serve as one of the premises as well. This is often referred to as circular reasoning. The example concerning Ford Motor Company in the text is a good example of this type of begging the question fallacy.
10. Post Hoc Ergo Propter Hoc: A lot of causal arguments are based on the fact that if one event occurs first and a second event follows the first event must have caused the second one. This, of course, is not always true.
On the three occasions that Terry has worn her Greek fishing cap, she has caught fish. Therefore, to ensure that she catch fish today, she should wear that cap.
There is no causal connection between wearing a cap and catching fish so this would be a case of false cause.
11. False Cause: One version of false cause is the Post Hoc Ergo Propter Hoc fallacy but false cause is a more general category. Many cases of false cause occur when correlation is confused with causation.
12. Red Herring: In red herring what usually happens is that the critic just drifts away from the original subject; hoping that the audience will forget what the original argument was! Here's an example:
Environmentalists argue that the use of pesticides on fruits and vegetables is dangerous to our health. But, fruits and vegetables contain many essential nutrients that can prevent disease and promote health. According to the FDA one of the best sources of vitamin C is orange juice and vegetables like broccoli contain a healthy dose of minerals such as iron. Clearly, fruits and vegetables are important to our health.
Now what was the original argument? It was about pesticides. But, then look what happens. The critic proceeds to change the subject to talk about vitamins and minerals. This has nothing to do with whether the environmentalists are correct about the dangers of pesticides! Classic red herring fallacy.
13: Slippery slope: this is sort of a variation on false cause. The main difference is that where false cause arguments are based on one cause, one effect, slippery slope is based on one cause which leads to a series of effects. So it has the form:
If A happens, then B will happen which will lead to C which in turn will lead to D. We don't want D to happen, so we better not let A happen. The problem is that it is very unlikely that the series will occur given the occurrence of A.
14. Equivocation: In equivocation, there is a single word in the argument that is used in two distinct ways. For example, the law of gravity is a law and laws can be repealed by the legislature. Therefore, the law of gravity can be repealed.
The problem with this argument is that it uses the word "laws" in two different senses. So, it equivocates on the word "law."
15: Naturalistic Fallacy: Also known as the Is-Ought fallacy. This has probably been around ever since people began thinking of ethics but David Hume formulated it in concrete terms in the 18th century. Basically the problem is that you cannot deduce from a set of facts what ought to be. For example, murders occur in this country. That's a fact. But, can we deduce from that fact that murders ought to occur? No. What's especially troubling is that we also cannot deduce that murders ought not to occur. That's the problem. How we solve this problem will be an important part of our look at ethical theory.