Introduction to Philosophy EXAM 1
a saJin3 qf the an- that "truth lies in
-ISAAC WATTS
Settt'on 1. 2
Evidence and Inference
Proving Your Point
T o arrive at the truth, we have to reason correctly. Philosophers have always appreciated this fact and have made the study of correct reason- ing-logic-one of their central concerns. Logic doesn't attempt to deter- mine how people in fact reason. Rather, it attempts to determine how people should reason if they want to avoid error and falsehood. Logical thinking is rational thinking, and rational thinking is that which is most likely to lead us to the truth.
When you're doing philosophy, you're trying either to determine whether a claim is true or to demonstrate that a claim is true. The first activity involves identifying and evaluating other people's arguments. The second involves constructing and defending your own arguments. Performing either of these tasks requires following certain rules and procedures. Mastering these rules and procedures will make you not only a better thinker but also a more persuasive speaker and writer.
What distinguishes a rational claim from an irrational one is that it's backed by good reasons. When you present reasons for believing that a claim is true, you're making an argument. The reasons you give for the claim you're making (which are themselves claims) are known as the premises of the argu- ment. The claim you're trying to make is known as the conclusion of the argument. An argument, then, is a group of claims consisting of one or more premises and a conclusion that supposedly follows from the premises.
ln ordinary parlance, any sort of disagreement is called an argument, but as we all know, these disagreements can be anything but logical. ln philosophy, the term "argument" is reserved for those claims in which there is supposedly a logical relation between the premises and the conclusion.
A good argument is one that provides a good reason for accepting its con- clusion. To help us distinguish good arguments from bad ones, logic identifies the ways in which premises and conclusion must be related in order for the conclusion to follow from them. Only when the conclusion logically follows
Chapter 1 • The Philosophical Enterprise
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trom the premises does an argument provide a good reason for accepting its conclusion.
Consider, for example, the following argument:
l. Roses are red.
2. Violets are blue.
3. Therefore daffodils are yellow.
:\ll of the premises in this argument are true, but it's not a good argument be- cause the conclusion doesn't follow from the premises. There is no logical re- lation between the premises and the conclusion. Consequently, it doesn't provide a good reason for believing the conclusion.
Identifying Arguments
The first step in identifying an argument is identifying its conclusion. The conclusion of an argument is the main point it's trying to make. It's the claim the argument is trying to justify. Identifying the conclusion is not always an easy task, however, because there may be several intermediate conclusions. In some cases, the author may even think that the conclusion is so obvious that it doesn't need to be stated. In many cases, however, the conclusion follows certain conclusion indicator words such as "thus," "therefore," "hence," "so," "then," "consequently," "as a result," "shows that," "means that," "implies that," "establishes that," and "can be concluded that." For example, consider the following arguments:
1. Only things made of flesh and blood can think. Therefore computers can't think.
2. You have no control over the neurons in your brain. It follows that you have no control over anything you do.
3. Everybody does it, so I should be allowed to do it, too.
In each of these cases, the conclusion is preceded by a conclusion indicator word.
Sometimes, however, the conclusion isn't preceded by anything. For example:
4. God exists since the world needs a designer. 5. She's a vegetarian because she thinks that eating meat is immoral.
6. The president's action is a mistake, for it will escalate terrorism, strengthen the resolve of our enemies, and alienate friendly states.
In these arguments, the conclusion comes before the premises. Once you've identified the conclusion, the next step in identifying an ar-
gument is to identify its premises. Premises are often preceded by certain premise indicator words such as "since," "because," "for," "if," "follows from," "given that," "provided that," and "assuming that." Like conclusions,
lo!Jic is the art of co11vi11c- iH!J us of mne truth. -JEAN DE LA BRUYERE
premise A reason given for accepting the conclusion of an argument.
conclusion The claim that an argu- ment is trying to establish.
argument A group of claims consisting of one or more premises and a conclusion that supposedly follows from the premises.
Evidence and Inference 29
Believ. nuthi>-IJ, nu matter when 'UU reaJ it, ur whu said · nu matter t( I said
it lljYCCS with yuur n reasun antlyuur uwn
-BUDDHA
In th spu:ler-web uf facts, man a truth is stranJf ed
-PAUL ELDRIDGE
however, premises can also be the first claim in an argument, as in the first three arguments.
The third step in identifying an argument is spelling out any unstated prem- ises. An argument with an unstated premise or conclusion is known as an en- thymeme. Most of the arguments you will encounter will fall into that category.
Consider again the first three arguments. Each of them has an unstated premise. Spelling out the unstated premise, they become:
7. Only things made of flesh and blood can think. Computers are not made of flesh and blood. Therefore computers can't think.
8. You have no control over the neurons in your brain. If you have no con- trol over the neurons in your brain, you have no control over anything you do. It follows that you have no control over anything you do.
9. Everybody does it. If everyone does it, I should be allowed to do it. So I should be allowed to do it, too.
Making explicit the implicit claims of an argument shows exactly what the argument is committed to. When filling in missing premises, it's important to be as fair as possible. You don't want to misrepresent the author's position. Since the purpose of identifying arguments is getting at the truth, the choice among different interpretations of an argument should be guided by the prin- ciple of charity: choose that interpretation which makes the most sense from a logical point of view. By following that principle, you'll put the argument in the best possible light.
Arguments come in two basic varieties: deductive and inductive. Good de- ductive arguments differ from good inductive ones in that they are valid. In a valid argument, the conclusion logically follows from its premises. In other words, in a valid argument, it's logically impossible for the premises to be true and the conclusion false, because the conclusion expresses what is implied by the combination of premises. Consider, for example, this argument:
1. If all that exists is matter in motion, then there are no disembodied spirits.
2. All that exists is matter in motion.
3. Therefore, there are no immaterial spirits.
This argument is valid because if the premises are true, the conclusion must be true. There's no way that the premises can be true and the conclusion false. So deductive arguments are said to be "truth preserving" because the truth of their premises guarantees the truth of their conclusions.
Inductive arguments, on the other hand, are not truth preserving because the truth of their premises doesn't guarantee the truth of their conclusions. Consider, for example, this argument:
l. Every raven that has ever been observed has been black.
2. Therefore, every raven that ever will be observed will be black.
It's possible for the premise of this argument to be true and the conclusion false. Because we haven't observed every raven, we can't be sure that there isn't a nonblack raven somewhere. And because we can't observe the future, we can't be sure that the future will resemble the past. So, unlike deductive
30 Chapter 1 • The Philosophical Enterprise
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arguments, which can establish their conclusions with certainty, inductive arguments can establish their conclusion with only a high degree of probabil- ity. A strong inductive argument is one that would establish its conclusion with a high degree of probability if its premises were true. ·
Deductive Arguments
Whether a deductive argument is valid depends on the form or structure of the argument. The form of an argument can be represented in many different ways, but one of the most effective is to substitute letters for the statements contained in the argument. Some statements are compound in that they con- tain other statements as constituents. To accurately represent the form of these statements, each constituent statement should be assigned a letter. For example, a conditional or if-then statement is compound because it contains at least two statements. To accurately represent the form of these statements, assign one letter to the statement following the "if" (known as the "an- tecedent"), and another to the statement following the "then" (known as the "consequent"). Using this method, four of the most common valid argument forms can be represented as follows.
Some Valid Argument Forms
Affirming the Antecedent (Modus Ponens)
If p, then q. p.
Therefore, q.
For example:
1. If the soul is immortal (p), then thinking doesn't depend on brain activity (q).
2. The soul is immortal (p). 3. Therefore, thinking doesn't depend on brain activity (q).
Denying the Consequent (Modus Tollens)
If p, then q. Notq.
Therefore, not p.
For example:
1. If the soul is immortal (p), then thinking doesn't depend on brain activity (q).
2. Thinking does depend on brain activity (not q).
3. Therefore, the soul is not immortal (not p).
Lu3ic is the armory of Yea.sun, (urnishetl with all offensive anti defensive W&llfUnS.
-THOMAS FULLER
enthymeme An argument with an unstated premise or conclusion.
principle of charity Choose that interpre- tation of an argument which makes the most sense from a logical point of view.
valid argument A deductive argument in which it's logically im- possible for the prem- ises to be true and the conclusion false.
Evidence and Inference 31
Reas n i.s mans instru- men for am'vin3 at the tru intellijenu i.s mans
ent for manipu- latin the world more
s(u01,· the former i.s ntia/~ human, tire latte. belon3s tu the ani- mal art of man.
-ERICH FROMM
Hypothetical Syllogism
If p, then q.
If q, then r. Therefore, if p, then r.
For example:
1. If the Federal Reserve Board raises interest rates, it will be more difficult to borrow money.
2. If it's more difficult to borrow money, home sales will f~ll. 3. Therefore, if the Federal Reserve Board raises interest rates, home sales
will fall.
Disjunctive Syllogism
Either p or q.
Notp.
Therefore, q.
For example:
1. Sally either walked or rode the bus.
2. She didn't walk.
3. Therefore, she rode the bus.
Because validity is a matter of form, any argument that exhibits any of these forms is valid, regardless of whether the statements it contains are true. So, to determine an argument's validity, it's not necessary to ascertain the truth of its premises.
To see this, consider this argument:
1. If one human is made of tin, then every human is made of tin.
2. One human is made of tin.
3. Therefore, every human is made of tin.
The premises and conclusion of this argument are false. Nevertheless, this ar- gument is valid because if the premises were true, then the conclusion would be true. A valid argument can have false premises and a false conclusion, false premises and a true conclusion, or true premises and a true conclusion. The one thing it cannot have is true premises and a false conclusion.
Since the purpose of logic is to help us discover the truth, there must be more to being a good deductive argument than being valid. In addi- tion, the premises must be true. When both conditions are met-when an argument is valid and its premises are true-the argument is said to be sound.
Only a sound argument provides a good reason for believing its conclu- sion. To determine whether you are justified in believing the conclusion of a
32 Chapter 1 • The Philosophical Enterprise
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Jeductive argument, then, you have to determine whether it's sound. This mYolves three steps: (1) identifying the premises and conclusion, (2) de- termining whether the argument is valid, and (3) determining whether the rremises are true. If the argument is not valid, there is no reason to pro- ceed to step 3, for in that case, the conclusion doesn't follow from the rremises.
There are many valid argument forms, and it is not feasible to memorize them all. But once you have ascertained the form of an argument, you can test it for validity by determining whether there is another argument with the sime form that would allow the premises to be true and the conclusion false. if so, the argument is invalid. Such an interpretation serves as a counter- example to the claim that the argument is valid.
S..mie Invalid Argument Forms
Affirming the Consequent
If p, then q. q.
Therefore, p.
let's test this argument form for validity by substituting the sentence "'Chicago is the capital of Illinois" for p and "Chicago is in Illinois" for q. Then we have:
L If Chicago is the capital of Illinois (p), then Chicago is in Illinois (q).
.:. Chicago is in Illinois (q).
3. Therefore, Chicago is the capital of Illinois (p).
Clearly, this argument is invalid. In a valid argument, you will recall, it's im- p,..ssible for the premises to be true and the conclusion false. But in this case, both of the premises are true and the conclusion is false. So any argument with this form does not provide a good reason for accepting its conclusion.
Here's another type of argument you may come across:
Denying the Antecedent
If p, then q. Notp.
Therefore, not q.
Can you imagine any situation in which the premises are true and the conclu- s1,c1n false? Suppose we substitute "Joe is a bachelor" for p, and "Joe is a male" k.r q. Then we get:
1. lf]oe is a bachelor (p), then Joe is a male (q).
.:. Joe is not a bachelor (not p).
3. Therefore, Joe is not a male (not q).
sound argument A valid deductive argu- ment that contains only true premises.
Evidence and Inference 33
All~ ths are easy to unde tand once they are disco red; the point is to disco r them.
GALILEO GALILEI
This argument is also invalid because it's possible for the premises to be true and the conclusion false. So anyone who uses this form of reasoning- no matter what statements they use in the place of p or q-has not proved their point.
Affirming a Disjunct
Either p or q.
p.
Therefore, not q.
In logic, the word "or" is usually understood inclusively. In the inclusive sense, a statement of the form p or q is true whenever p or q or both are true. The word "or" can also be understood exclusively, however. In the ex- clusive sense, a statement of the form p or q is true whenever p or q but not both are true. The fallacy of affirming a disjunct occurs when an inclusive or is interpreted exclusively. For example:
1. Either the car battery is dead or the car is out of gas.
2. The car battery is dead.
3. Therefore, the car is not out of gas.
This argument is invalid because it's possible for both disjuncts to be true: the car could have a dead battery and be out of gas at the same time. Conse- quently, from the fact that one is true, we cannot validly conclude that the other is not true.
Inductive Arguments
Even though inductive arguments are not valid, they can still give us good reasons for believing their conclusions, provided that certain conditions are met. An inductive argument that would establish its conclusion with a high degree of probability if its premises were true is known as a strong argument. A strong inductive argument with true premises is known as a cogent argu- ment. To get a better idea of what constitutes a strong inductive argument, let's examine some common forms of induction.
Enumerative Induction
Enumerative induction is the sort of reasoning we use when we arrive at a generalization about a group of things after observing only some members of that group. The premise of a typical enumerative induction is a statement reporting what percentage of the observed members of a group have a partic- ular property. The conclusion is a statement claiming that a certain percent- age of the members of the whole group have that property. Enumerative induction, then, has the following form:
34 Chapter I • The Philosophical Enterprise
ises to be true f reasoning- as not proved
the inclusive q or both are er. In the ex- !' or q but not inclusive or is
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give us good JOditions are 1 with a high tg argument. cogent argu- ,--e argument,
e arrive at a members of a statement aYe a parti.c- ain percent- ::numerative
L X percent of the observed members of A are B.
2- Therefore, X percent of the entire group of A are B.
h.T example, suppose you use enumerative induction to argue from the obser- 'i'3tion that 54 percent of the students in your college are female to the con- cru:.ion that 54 percent of all college students are female. This would be a ittong argument only if your sample were sufficiently large and sufficiently rerresentative of the entire group of college students. A sample is considered rerresentative of a group when every member of the group has an equal .:ha.nee to be part of the sample. If your sample consisted of those students ,mending a small, select engineering school, then your argument would not be \·ery strong because your sample would be too limited and unrepresenta- m·e. But if your sample consisted of those students attending a large state university with a national reputation, your argument would be stronger be- .:ause your sample would be larger and more representative.
Analogical Induction
\X'hen we show how one thing is similar to another, we draw an analogy be- tween them. When we claim that two things that are similar in some respects are similar in some further respect, we make an analogical induction. For ex- ample, prior to the various missions to Mars, NASA scientists may have ar- ?Ued as follows: Earth has air, water, and life. Mars is like Earth in that it has air and water. Therefore, it's probable that Mars has life. The form of such analogical inductions can be represented as follows:
l. Object A has properties F, G, H, and so on, as well as the property Z.
2. Object B has properties F, G, H, and so on. 3. Therefore, object B probably has property Z.
Like all inductive arguments, analogical inductions can only establish their o,mclusions with a certain degree of probability. The more similarities be- tween the two objects, the more probable the conclusion. The fewer similar- ities, the less probable the conclusion.
The dissimilarities between Earth and Mars are significant. The Martian .1tmosphere is very thin and contains very little oxygen, and the water on ~fars is trapped in ice caps at the poles. So the probability of finding life on Mars is not very high. Mars was more like Earth in the past, however. So the probability of finding evidence of past life on Mars is greater.
NASA scientists are not the only ones who make analogical inductions. This kind of reasoning is used in many other fields, including medical re- ~arch and law. Whenever medical researchers test a new drug on laboratory animals, they are making an analogical induction. Essentially, they are argu- mg that if this drug has a certain effect on the animals, then it's probable that ,t \\'ill have the same sort of effect on human beings. The strength of such arguments depends on the biological similarities between the animals and hu- mans. Rats, rabbits, and guinea pigs are often used in these kinds of experi- ments. Although they are all mammals, their biology is by no means identical
strong argument An inductive argument that would establish its conclusion with a high degree of proba- bility if its premises were true.
cogent argument A strong inductive argu- ment that contains only true premises.
Evidence and Inference 35
to ours. So we cannot be certain that any particular drug will affect us in the same way that it affects them.
The American legal system is based on precedents. A precedent is a case that has already been decided. Lawyers often try to convince judges of the merits of their case by citing precedents. They argue that the case before the court is similar to one that has been decided in the past, and since the court decided one way in that case, it should decide the same way in this case. The opposing attorney will try to undermine that reasoning by highlighting the differences between the case cited and the current case. Which side wins such court cases is often determined by the strength of the analogical argu- ments presented.
Hypothetical Induction (Abduction, Iriference to the Best Explanation)
We attempt to understand the world by constructing explanations of it. Not all explanations are equally good, however. So even though we may have arrived at an explanation of something, it doesn't mean that we're justified in believing it. If other explanations are better, then we're not justified in believing it.
Inference to the best explanation has the following form:
1. Phenomenon p.
2. If hypothesis h were true, it would provide the best explanation of p. 3. Therefore, it's probable that his true.
The American philosopher Charles Sanders Peirce was the first to codify this kind of inference, and he dubbed it "abduction" to distinguish it from other forms of induction.
Inference to the best explanation may be the most widely used form of inference. Doctors, auto mechanics, and detectives (as well as you and I) use it almost daily. Anyone who tries to figure out why something hap- pened uses inference to the best explanation. Sherlock Holmes was a mas- ter of inference to the best explanation. Here's Holmes at work in A Study in Scarlet:
I knew you came from Afghanistan. From long habit the train of thoughts ran so swiftly through my mind that I arrived at the conclusion without being conscious of intermediate steps. There were such steps, however. The train of reasoning ran, 'Here is a gentleman of a medical type, but with the air of a military man. Clearly an anny doctor, then. He has just come from the tropics, for his face is dark, and that is not the natural tint of his skin, for his wrists are fair. He has undergone hardship and sickness, as his haggard face says clearly. His left arm has been injured. He holds it in a stiff and unnatural manner. Where in the tropics would an English army doctor have seen much hardship and got his arm wounded? Clearly in Afghanistan.' The whole train of thought did not occupy a second. I then remarked that you came from Afghanistan, and you were astonished. 18
Chapter 1 • The Philosophical Enterprise
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A.lthough this passage appears in a chapter entitled "The Science of De- Juction," Holmes is not using deduction here, because the truth of the prem- :ISeS does not guarantee the truth of the conclusion. From the fact that '«·arson has a deep tan and a wounded arm, it doesn't necessarily follow that he has been in Afghanistan. He could have been in California and cut him- x>If surfing. Properly speaking, Holmes is using abduction, or inference to the best explanation, because he arrives at his conclusion by citing a number of tacts and coming up with the hypothesis that best explains them.
Often what makes inference to the best explanation difficult is not that no explanation can be found, but that too many can be found. The trick is to identify which among all the possible explanations is the best. The goodness <.'tan explanation is determined by the amount of understanding it produces, and that is determined by how well it systematizes and unifies our knowledge. '\'i·e begin to understand something when we see it as part of a pattern, and the more that pattern encompasses, the more understanding it produces. The extent to which a hypothesis systematizes and unifies our knowledge can be measured by various criteria of adequacy, such as consistency, both internal ,mJ external; simplicity, the number of assumptions made by a hypothesis; s.:,,pe, the amount of diverse phenomena explained by the hypothesis; conser- wrism, how well the hypothesis fits with what we already know; and fruitful- r.icss, the ability of a hypothesis to successfully predict novel phenomena. Let's uke a closer look at how these criteria are used to evaluate hypotheses.
The first requirement of any adequate hypothesis is consistency. Not only must an adequate hypothesis be internally consistent-consistent with nself-but it must also be externally consistent--consistent with the data it is :.-urposed to explain. If a hypothesis is internally inconsistent-if it's self-con- tradictory-it can't possibly be true. Thus one of the most effective ways to re- fute a theory is to show that it harbors a contradiction. (This technique, you will recall, is the one that Socrates used against Euthyphro.) If a hypothesis is externally inconsistent-if it's inconsistent with the data it's supposed to ex- riain-there's reason to believe that it's false. The data, of course, could be mistaken, but until we know that, we shouldn't accept the theory.
Other things being equal, the simpler a hypothesis is-the fewer assump- tions it makes-the better it is. If phenomena can be explained without mak- mg certain assumptions, there's no reason to make them. So a theory that makes unnecessary assumptions is unreasonable. Medieval philosopher William of Occam put the point this way: "Entities should not be multiplied beyond necessity." In other words, you shouldn't assume the existence of any- thing that's not needed to explain the phenomena. This principle has come t1..1 be known as "Occam's razor" because it's used to shave off unneeded enti- ties from theories. (This principle, which is also known as "the principle of parsimony," looms large in Carl Sagan's book and movie entitled Contact.)
Scope-the amount of diverse phenomena explained by a theory-is also ID important consideration in theory evaluation. If two theories do equally well with respect to the other criteria of adequacy but one has more scope, it's dearly the better theory, for it has greater explanatory power.
Conservatism-the quality of fitting well with existing theories-is a mark .:i a good theory because if accepting a theory requires rejecting a good deal
criteria of adequacy The features that dis- tinguish a good theory from a bad one: consis- tency (lack of contra- dictions), simplicity (quality of relying on only a small number of assumptions), scope (the amount of di- verse phenomena ex- plained), conservatism ( quality of fitting well with existing theories), and fruitfulness ( the number of new facts predicted or problems solved) .
Evidence and Inference 37
When ea!t'nj with people, let u.s 'Cmember we are not di. i'nj with crea-
lo3ic. We are with creatures of , creatures with prejudices
anti tivatetl by pride anti v. 11ity.
DALE CARNEGIE
of what we've already established, then it may diminish our understanding. Instead of systematizing and unifying our knowledge, it may fragment it. A theory can make up in scope and simplicity what it lacks in conservatism, however. In that case, it may be worthy of acceptance.
In science, fruitfulness is determined by the number of successful, novel predictions a theory makes. In philosophy, it's determined by the number of problems it solves. In both cases, it's evidence for the truth of the hypothesis because the best explanation of the fact that a theory makes a successful, novel prediction or solves problems is that it's true.
Unfortunately, there is no formula for applying the criteria of adequacy. We can't quantify how well a hypothesis does with respect to any particular criterion, nor can we rank the criteria in order of importance. At times, we may rate conservatism more highly than scope, especially if the hypothesis in question is lacking in fruitfulness. At other times, we may rate simplicity higher than conservatism, especially if the hypothesis has at least as much scope as any other hypothesis. Choosing among theories isn't the purely logi- cal process it is often made out to be. Like judicial decision making, it relies on factors of human judgment that resist formalization.
This doesn't mean that the process of theory selection is subjective, how- ever. There are many distinctions we can't quantify that are nevertheless perfectly objective. The point at which day turns into night or a hirsute person becomes bald can't be precisely specified. But the distinctions between night and day or baldness and hirsuteness are as objective as they come. There are certainly borderline cases about which reasonable people can disagree, but there are also clear-cut cases where disagreement would be irrational. It would simply be wrong to believe that a person with a full head of (living) hair is bald. It would be equally wrong to believe that a theory that does not meet the criteria of adequacy as well as its competitors is the better theory.
Informal Fallacies
When we give reasons for accepting a claim, we are making an argument. If the premises are acceptable, and if they adequately support the conclusion, then our argument is a good one. If not-if the premises are dubious, or if they do not justify the conclusion-then our argument is fallacious. A falla- cious argument is a bogus one, for it fails to do what it purports to do: provide a good reason for accepting a claim. Unfortunately, logically fallacious argu- ments can be psychologically compelling. Because most people have never learned the difference between a good argument and a fallacious one, they are often persuaded to believe things for no good reason. To avoid holding irra- tional beliefs, then, it is important to understand the ways in which an argu- ment can fail.
An argument is fallacious if it contains (1) unacceptable premises, (2) ir- relevant premises, or (3) insufficient premises.19 Premises are unacceptable if they are at least as dubious as the claim they are supposed to support. In a good argument, the premises provide a firm basis for accepting the conclu- sion. If the premises are shaky, the argument is inconclusive. Premises are
38 Chapter 1 • The Philosophical Enterprise
particles. So they must be alive too." To argue in this way is to ignore the very real difference between parts and wholes.
Argument against the Person When someone tries to rebut an argument by criticizing or denigrating its presenter rather than by dealing with the is- sues it raises, that person is guilty of the fallacy of argument against the person. This fallacy is referred to as ad hominem, or "to the man." For ex- ample: "This theory has been proposed by a believer in the occult. Why should we take it seriously?" Or: "You can't believe Dr. Jones's claim that there is no evidence for life after death. After all, he's an atheist." The flaw in these arguments is obvious: An argument stands or falls on its own mer- its; who proposes it is irrelevant to its soundness. Crazy people can come up with perfectly sound arguments, and sane people can talk nonsense.
Genetic Fallacy To argue that a claim is true or false on the basis of its origin is to commit the genetic fallacy. For example: "Jones's idea is the result of a mystical experience, so it must be false (or true)." Or: "Jane got that mes- sage from a Ouija board, so it must be false (or true)." These arguments are fallacious because the origin of a claim is irrelevant to its truth or falsity.
Appeal to Unqualified Authority We often try to support our views by cit- ing experts. This sort of appeal to authority is perfectly valid, provided that the person cited really is an expert in the field in question. If not, it is fal- lacious. Celebrity endorsements often involve fallacious appeals to author- ity because being famous doesn't necessarily give you any special expertise. The fact that Dionne Warwick is a great singer, for example, doesn't make her an expert on the efficacy of psychic hotlines.
Appeal to the Masses A remarkably common but fallacious form of reason- ing is, "It must be true (or good) because everybody believes it (or does it)." Mothers understand that this is a fallacy; they often counter this argu- ment by asking, "If everyone jumped off a cliff, would you do it too?" Of course you wouldn't. What this shows is that just because a lot of people believe something or like something doesn't mean that it's true or good. A lot of people used to believe that the earth was flat, but that certainly didn't make it so. Similarly, a lot of people used to believe that women should not have the right to vote. Popularity is not a reliable indication of either reality or value.
Appeal to Tradition We appeal to tradition when we argue that something must be true (or good) because it is part of an established tradition. For ex- ample: "Astrology has been around for ages, so there must be something to it." Or: "Mothers have always used chicken soup to fight colds, so it must be good for you." These arguments are fallacious because traditions can be wrong. This becomes obvious when you consider that slavery was once an established tradition. The fact that people have always done or believed something is no reason for believing that we should continue to do or be- lieve something.
Appeal to Ignorance The appeal to ignorance comes in two varieties: using an opponent's inability to disprove a conclusion as proof of the conclu- sion's correctness, and using an opponent's inability to prove a conclusion
Chapter 1 • The Philosophical Enterprise
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as proof of its incorrectness. In the first case, the claim is chat since there is no proof that something is true, it must be false. For example: "There is no proof that the parapsychology experiments were fraudulent, so I'm sure they weren't." In the second case, the claim is that since there is no proof chat something is false, it must be true. For example: "Bigfoot must exist because no one has been able co prove that he doesn't." The problem with these arguments is that they take a lack of evidence for one thing to be good evidence for another. A lack of evidence, however, proves nothing. In logic, as in life, you can't get something for nothing.
Appeal to Fear To use the threat of harm to advance one's position is to commit the fallacy of the appeal to fear. It is also known as "swinging the big stick." For example: "If you do not convict this criminal, one of you may be her next victim." This is fallacious because what a defendant might do in the future is irrelevant to determining whether she is responsible for a crime committed in the past. Threats extort; they do not help us arrive at the truth.
lns1ficient Premises
Hasty Generalization You are guilty of hasty generalization or jumping to conclusions when you draw a general conclusion about all things of a cer- tain type on the basis of evidence concerning only a few things of that type. For example: "Every medium that's been investigated has turned out to be a fraud. You can't trust apy of them." Or: "I know one of those psy- chics. They're all a bunch of phonies." You can't make a valid generaliza- tion about an entire class of things from observing only one or even a number of them. An inference from a sample of a group to the whole group is legitimate only if the sample is representative-that is, only if the sample is sufficiently large and every member of the group has an equal chance to be part of the sample.
Faulty Analogy An argument from analogy claims that things that resemble one another in certain respects resemble one another in further respects. For example: "Earth has air, water, and living organisms. Mars has air and water. Therefore Mars has living organisms." The success of such argu- ments depends on the nature and extent of the similarities between the two objects. The greater their dissimilarities, the less convincing the argu- ment will be. For example, consider this argument: "Astronauts wear hel- mets and fly in spaceships. The figure in this Mayan carving seems to be wearing a helmet and flying in a spaceship. Therefore it is a carving of an ancient astronaut." Although features of the carving may bear a resem- blance to a helmet and spaceship, they may bear a greater resemblance co a ceremonial mask and fire. The problem is that any two things may have some features in common. Consequently, an argument from analogy can be successful only if the dissimilarities between the things being compared are insignificant.
False Cause The fallacy of false cause consists of supposing that two events are causally connected when they are not. People often claim, for example,
Fallacies Jo not cease to be fallacies because they he- come fashions.
-G. K. CHESTERTON
Evidence and Inference 41
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that because something occurred after something else, it is caused by it. Latin scholars dubbed this the fallacy of post hoc, ergo propter hoc, which means "After this, therefore because of this." Such reasoning is fallacious because from the fact that two events are constantly conjoined, it doesn't follow that they are causally related. Night follows day, but that doesn't mean that day causes night.
Summary
Arguments come in two basic varieties: deductive and inductive. In a valid deductive argument, it's impossible for the premises to be true and the con- clusion false. A deductive argument is sound if it's valid and its premises are true. In a strong inductive argument, it's improbable for the premises to be true and the conclusion false. An inductive argument is cogent if it's strong and its premises are true.
Hypothetical induction, or inference to the best explanation, is one of the most common inductive arguments. The goodness of an explanation is determined by how much understanding it produces, and the amount of understanding produced by an explanation is determined by how well it sys- tematizes and unifies our knowledge. The extent to which a hypothesis ac- complishes this goal can be measured by various criteria of adequacy, such as consistency, simplicity, scope, conservatism, and fruitfulness.
Study Questions
1. What is the difference between deductive and inductive arguments?
2. What is a valid deductive argument?
3. What is a sound deductive argument?
4. What is a strong inductive argument?
5. What is a cogent inductive argument?
6. What is the logical form of affirming the antecedent, denying the conse- quent, hypothetical syllogism, disjunctive syllogism, affirming the conse- quent, denying the antecedent?
7. What is the logical form of enumerative induction, analogical induction, hypothetical induction?
8. What are the criteria of adequacy for good explanations?
9. What are informal fallacies?
Discussion Questions Determine whether the following deductive arguments are valid or invalid, and, if valid, whether they are sound or unsound.
1. If it rained, the streets are wet. The streets are wet. So it must have rained.
Chapter 1 • The Philosophical Enterprise
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2. If Richard Roe is willing to testify, then he's innocent. But he's not will- ing to testify. Therefore he's not innocent.
3. If Bogota is north of New Orleans, and New Orleans is north of Mexico City, then Bogota is north of Mexico City. Bogota is not north of New Orleans. Therefore Bogota is not north of Mexico City.
Determine whether the following inductive arguments are strong or weak, and, if strong, whether they are cogent or uncogent.
4. Every day you've lived has been followed by another day in which you have been alive. Therefore every day you ever will live will be followed by another day in which you are alive. (You will live forever.)
5. Every day you've lived has been a day before tomorrow. Therefore every day you ever will live will be a day before tomorrow. (You will die tonight.)
6. Almost every Mummers Parade has been held in freezing weather. Therefore, probably, this year's Mummers Parade will be held in freezing weather.
7. A recent Roper poll found that a significant number of Americans have woken up paralyzed, lost time, seen inexplicable lights, found puzzling scars on their bodies, and felt as if they were flying. So a significant number of Americans must have been abducted by aliens.
Identify the informal fallacy committed in the following arguments.
8. Nobel Prize winner Linus Pauling says we should take massive doses of vitamin C every day. Therefore massive doses of vitamin C must be good for you.
9. Quartz crystals cure colds because after I wore a quartz crystal around my neck, my cold went away.
lO. Society's interest in the occult is growing. Therefore Joe's interest in the occult is growing.
11. Either we're going to lose the war on terrorism or we'll have to give up some of our civil liberties.
Internet Inquiries
1. How logical are you? To find out, play the "Elementary, My Dear Wason" game at The Philosophers' Magazine Web site: http://www .philosophyexperiments.com/wason/Default.aspx
2. How good at probability are you? To find out, play the "Urn a Red Ball" game at The Philosophers' Magazine Web site: http://www .philosophyexperiments.com/balls/Default.aspx
3. Find at least five examples of fallacious arguments by searching blogs, editorials, articles, and so on. Identify the fallacy that each commits.
Evidence and Inference 43