Burden of Proof Arguments                                                                 (Problems printing? Click here.)

IMPORTANT NOTICE FOR SANTA ANA COLLEGE STUDENTS

Class will not meet on Thursday, March 27th
Instead, we will have a Field Trip.

Your Field trip assignment is to attend one session of the CSUF Philosophy Symposium, and write a short report on the logic of what was discussed.
(Extra sessions, extra credit.)
Attendance at any Symposium Session counts as class attendance, but is not mandatory.
If you can't make in into Fullerton for the Symposum, contact me for an equivalent assignment.

For more info and directions, download and print symp01 and symp02.

Now, on to Burden of Proof.

At this point, you may find yourself wondering what happens if all the arguments on both sides succumb to counter arguments so that it turns out that there are no good arguments on either side of a question. (You don't find yourself wondering that? Well, pretend you do. work with me here.) In order to fully answer that question, I have to make a distinction between personal opinion and knowledge. Here, I'm going to define "knowledge" as whatever beliefs we have that are appropriately backed up by evidence and logic. By "personal opinion," I mean whatever beliefs you happen to have. Since your own personal beliefs don't have to be backed up by evidence and logic, it follows that not all of your personal beliefs will count as knowledge. (And that's okay.) Now, if you're just worried about your own personal opinion, and it turns out that there are no good arguments on either side of a question, then you can just go on believing whatever it was you believed before. If you're worried about knowledge, the situation is a bit more complicated. If you find yourself asking, "given that there are no good arguments on either side of this question, what do we know?" The answer will depend on whether one side in the question happens to bear the burden of proof.

The concept of burden of proof is easiest to explain in terms of your own personal opinion. Crudely put, you need a reason to change your mind about anything. Someone who wants you to change your mind therefore has to come up with a reason that works for you. On the other hand, as far as your personal beliefs are concerned, you don't have to come up with a reason for you to believe whatever you happen to believe. (And neither does anyone else have to come up with reasons for believing whatever their personal opinions happen to be.) The fact that someone who wants to change your mind has to come up with a reason while you don't have to come up with a reason for keeping your pre-existing opinion is referred to as him bearing the burden of proof and you not bearing the burden of proof.

In terms of knowledge, the situation is way more complicated. Broadly, there are two general situations where the supporter of a particular claim clearly bears the burden of proof. First, there is the situation where someone is advancing a claim that is clearly inconsistent with our present knowledge. Second, there is a situation where someone is claiming that some action is morally wrong.

When I use the term "present knowledge," I definitely don't mean whatever it is that the majority of people happen to believe at any particular moment. Lots of things that lots of people believe have no basis whatsoever in any kind of evidence or logic. What I mean by present knowledge is the body of information that represents our best efforts so far at discovering the truth. These are the beliefs that, so far as we have been able to make out, are the most likely to be true of any beliefs that we might have. To say that we know something does not really mean that it is undoubtedly and unquestionably true. Rather it means that not only do we have good reason to believe it, we also have much better reason to believe it than we do for any competing belief. Thus for something to really count as part of present knowledge, it must already be backed up by evidence and logic. Beliefs that contradict present knowledge thus start out with at least one strike against them in that whatever argument established that present knowledge in the first place also tends to contradict whatever contradicts that present knowledge. To put it another way, if something contradicts established knowledge, then that by itself means that there is already an argument against it. If there is in fact no good argument for it, then we can and should conclude that it is false.

Morality is different. For one thing, there is much more expert disagreement about morality then there is about any other subject. For another, while it is perfectly fine for us to go through our lives ignoring the facts of physics and biology, it is deeply irresponsible for someone to go through life ignoring the facts of morality. People who violate morality are evil, and deserve to be shunned, yelled at, pelted with rotten fruit, or worse. But moral rules cannot exist without justification. If there is a rule that we all should follow, then that rule will come with a clear and explainable justification. If a purported moral rule fails to come with a clear justification, then it simply is not a moral rule. If someone tells you that something you want to do is morally wrong but cannot logically show that what you want to do will hurt anyone or anything, or that it will violate somebody's rights, or that there is some other logically sound justification, then you have no rational reason to believe that person.

Someone might argue that some moral rules are so well-established that they form part of present knowledge. The problem with that is that many things that have been believed to be moral rules for many generations have turned out to be either not moral rules to all or actually evil. As you review the struggle for human rights across the history of the world, there is one thing that is an absolute constant. Whatever the struggle, the people who were trying to maintain the old system of slavery, of racial segregation, of subjugation of women, of homophobia, of religious persecution or whatever were absolutely convinced that they, and only they, were fighting to preserve morality in the face of a rising tide of evil. The fact that a "moral" rule is well-established in the minds of the majority of people has nothing to do with whether or not it really is a moral rule. If it is a moral rule, then those supporting it will be able to cite good reasons in support of it. If it is not a moral rule, then those opposing it only have to show that it is not supported by evidence and logic.

There are two things that make this burden of proof business even more complicated, and I will put off full discussion of them until another lecture. For now I will just say that some moral issues turn out to have moral principles supporting both sides of the question, so that it's not clear which side really bears the burden of proof, and that it is sometimes hard to tell what our present knowledge really is. This means that burden of proof is itself often the subject of arguments, which gives rise to burden of proof arguments and fallacies, which I shall describe later.

For now, I'm going to give you a set of pairs of claims, some with answers, some without, for which you should determine which speaker bears the burden of proof at the start of the discussion. Remember that this class is about knowledge, rather than anybody's personal opinion. Therefore, you should not assign burden of proof based on whether or not you think a claim is true. You should assign it based on whether the speaker is making a positive moral claim, or a claim that is significantly inconsistent with our present knowledge.

Albert. The CIA killed John F. Kennedy.
Beth. No they didn't.

Charlie. The CIA overthrew the democratically elected government of Jacobo Arbenz of Guatemala in 1954.
Desmond. No they didn't.

Edgar. Ghosts exist.
Caitlyn. No they don't.

Gerald. Life exists on other planets.
Harold. No it doesn't.

Irene. It's morally wrong to kill innocent people for food when you have sufficient vegetables available.
Jessica. No it isn't.

Karen. It's morally wrong to kill innocent animals for food when you have sufficient vegetables available.
Linda. No it isn't.

Michelle. It's morally okay for two unattached consenting adults to have sex outside of marriage.
Nina. No it isn't.

Ophelia. It's morally okay to detonate nuclear devices in every city in the world.
Paula. No it isn't.

(Answers)

For some final practice, explain where the burden of proof lies for each one of the following issues. I have phrased them as contradictory sentence pairs, so circle the side that bears the burden of proof. If the location of the burden of proof is unclear, circle both.

9. Astrology can predict the future. Astrology cannot predict the future.

10. Chiropractic works. Chiropractic doesn't work.

11. Natural selection is true. Natural selection is not true.

12. Socialism is evil. Socialism is not evil.

13. We should ban affirmative-action. We should not ban affirmative-action.

14. Cigarette companies should be allowed to target black people. Cigarette companies should not be allowed to target black people.

15. Bill Clinton's Tomahawks hit a terrorist training camp. Bill Clinton's Tomahawks did not hit a terrorist training camp.

16. Elephants can wear people's pajamas. Elephants cannot wear people's pajamas.

17. Ray Charles is God. Ray Charles is not God.

18. We only use 10 percent of our brains. We don't only use 10 percent of our brains.

19. Deterrence will work on Saddam. Deterrence will not work on Saddam.

20. As originally written, the Constitution predominantly protected the interests of the ruling class. As originally written, the Constitution did not predominantly protect the interests of the ruling class.

21. It is wrong to alter one's state of consciousness. It is not wrong to alter one's state of consciousness.

22. Drug laws are justified by the prevalence of drug crime. Drug laws are not justified by the prevalence of drug crime.

23. A doctor's gut is more likely to be right than the appropriate tests. A doctor's gut is not more likely to be right than the appropriate tests.

24. Cat juggling is morally wrong. Cat juggling is not morally wrong.

Burden of Proof Arguments

The idea behind burden of proof arguments is fairly simple. Some claims can be accepted without proof, so long as there is no good argument to the contrary. Other claims can not be rationally accepted without some good argument to back them up. Generally speaking, claims that we already have good reason to believe tend to fall into the first category, while new claims, that contradict our existing knowledge, fall into the second category. Thus burden of proof arguments are usually (but not always) used to reject new claims.

The way it usually works is that someone claims we should believe some new claim that contradicts our already established knowledge. He claims to have discovered a new form of radiation, or he knows who really killed Kennedy, or that George W. Bush is really Elvis, etc.. We ask him to give us a reason to believe him. He comes up with no real reasons, or maybe he just comes up with fallcaious reasons. Nothing he says has persuasive force. We reject the claim. It's important to note that logically we're not just entitled to say "maybe, maybe not." We're logically entitled to say "not true." His failure to come up with reasons is itself a good reason to reject his claim. If we have to make up our minds, we should say no. If we don't absolutely have to make up our minds at that time, we can reasonably suspend judgement, but we still have a good reason to reject the claim.

The following are all good burden-of-proof arguments.

Nathan. So-called "cold-fusion" conflicts with well-established nuclear theory. People who claim cold-fusion exists have failed to produce any replicable results. Therefore, cold-fusion does not exist.

Cindy. Believers in the 100-miles-per-gallon carburettor have failed to offer any credible evidence for it's existence. Therefore, no 100-miles-per-gallon carburettor exists.

Boyd. Astrologers have failed to offer any valid evidence that astrology has any special predictive power. Therefore, astrology has no special predictive power.

Steve. People who claim that cat-juggling is morally wrong have failed to offer any reasonable arguments against cat-juggling. Therefore, cat juggling is not morally wrong.

Giordanno. People who believe in Arkt-Rcckt-Siiv-Ek the Flaming Lizard Goddess have failed to offer any non-fallacious argument for her existance. Therefore, Arkt-Rcckt-Siiv-Ek does not exist.

It's important to remember that in evaluating these arguments we should take the position of a reasonable person who presently neither believes nor disbelieves in the conclusion, but who is willing to be persuaded by a reasonable argument. As in any argument, it's not necessarily irrational for someone to choose to disregard the argument and choose to disbelieve the conclusion. But such a person would not be deciding on rational grounds.

Nathan's argument is based on the fact that science at all times has an existing body of knowledge that it seeks to expand and refine. This body of knowledge of course grows and changes as science goes on. Sometimes it changes quite radically, with existing theories being thrown out entirely. But it doesn't change without a good reason, and when no good reasons are around, it actually has a good reason not to change. Why? Simply because science has again and again turned out to be right when the principle of not changing without good reason has been followed. People who have tried to change science without producing reliable evidence have invariably turned out to be wrong. Thus the fact that some claim conflicts with science is itself a good reason to reject that claim unless it is supported by evidence. If it isn't supported by evidence, then the mere fact it conflicts with established science gives us a rational reason to reject it. The burden of proof always lies on he who would change scientific knowledge.

Cindy's argument is based on the fact that society also has an existing body of knowledge that some people seek to expand and refine. This body of knowledge grows and changes roughly the same way as scientific knowledge. But it shouldn't change without a good reason, and when no good reasons are around, it shouldn't have to change at all. Thus the fact that some claim conflicts with society's established knowledge is itself a good reason to reject that claim unless it is supported by evidence. But notice that "established body of knowledge" is not the same as "common belief." Cindy's argument doesn't rely on the fact that no-one believes in 100-miles-per-gallon carburettors. It relies on the fact that such carburettors aren't part of the common experience of anyone she knows. No-one owns one, no-one she know knows anyone who owns one. Car dealers do not sell them, and so on. The established body of knowledge of society is the knowledge that society has built up through actual experience, not whatever the majority of people in society just happen to believe.

Boyd's argument is based on the same body of knowledge as Cindy's, only here, common belief tends to run the other way. Many or most people in our society believe that astrologers can predict events or divine personality features with an accuracy and scope that goes far beyond mere guesswork or cold reading. Boyd's argument relies on the fact that reliable information has only ever been produced by careful assessment of relevant data. Collecting data that has no connection with the subject has never worked in any other context, so it's unlikely that it would work for astrologers. This is enough to shift the burden of proof over to the astrologers. Since they bear the burden of proof, and have never met that burden, we have very good reasons not to believe in astrology.

Steve's argument relies on something completely different. Morality is something we never experience directly. We can experience things like pain and pleasure, constraint and freedom, feelings of shame and guilt, and know about other people experiencing those things, but no-one ever has a direct experience of something being moral or immoral. The morality of an action is something we have to figure out, and that can be difficult. It's especially difficult to come up with positive arguments in favor of things being morally allowable. (Can you come up with a positive argument that proves you have a right to go to college? Can you prove that anyone has a right to go to college? Or a right to not go to college?) So in moral reasoning (unlike logic) we have a general rule that any action is considered morally allowable unless someone can come up with a credible argument that it is morally wrong. Thus Steve doesn't have to offer any proof that cat-juggling is morally okay. The mere fact that his opponants haven't come up with any proof that it's not is enough to prove them wrong.

Giordanno's argument is logically similar to Steve's. Although people have feelings they attribute to the supernatural, no-one has actual experience of it. Since the number of possible supernatural entities is infinite, and most of them are such that if one of them exists, none of the others can, it makes sense to believe in none of them without incontrovertable evidence. Thus, even if everybody believes that they have experience of Arkt-Rcckt-Siiv-Ek the Flaming Lizard Goddess. Even if there are Flaming Lizard coloring books, folk stories, myths and unexplained scorch marks, as long as there's no evidence that can't be easily explained by ordinary means, (such as hallucinations, sleep paralysis, self-delusion, lying, and pious fraud) we have very good reason not to believe in Arkt-Rcckt-Siiv-Ek. (That's not to say we can't believe in the Flaming Lizard Goddess, just that we can't say we have a rational reason to do so.)

So far, we've looked at burden of proof arguments aimed at rejecting some new claim. What about burden of proof arguments against old claims? Well, the logic is the same, except that the claim in question has had time to become an old claim. Consider the following conversation.

Raymond. You know that we only use ten percent of our brains, so if we could harness...
Reilly. Wait, wait, wait. Can you prove we only use ten percent of our brains?
Raymond. I don't have to. It's part of our established background knowledge. Burden of proof arguments only work on claims that conflict with our established background knowledge.
Reilly. But it does conflict with established knowledge. If it were true, neuroscience would only study ten percent of the brain, brain surgeons would only operate on ten percent, and so on. Nobody who actually studies the brain says we only use ten percent, and textbooks that show the brain describe a particular use for every part of it. I've never seen a picture of the brain that picks out ten percent and says, "this is the only part we use." Have you?
Raymond. Well, everyone I know says that we only use ten percent of our brains, so it is established background knowledge!
Reilly. No, that's just rumor. Knowledge is not the same as popular belief.

The trick to determining whether something is established background knowledge is to ask how a belief became common. If it became common because somebody studied the question and concluded that it was true, then it's established background knowledge. If it became common because it sounded good to some people, then it's not established background knowledge.

Thus there are three basic questions that should be asked about any burden of proof argument.

1. Does the conclusion of the argument fit with our established beliefs so firmly that we can't deny that conclusion without also implying that at least some of our background beliefs are false?

2. Are our background beliefs about this topic based on some kind of foundation?

3. Is it really true that the opposing side has no credible arguments against that conclusion?

If the answer to any of these questions is "no," then the burden of proof argument will not work. If the opposite conclusion turns out to fit our background beliefs, or if the beliefs the opposite conclusion doesn't fit aren't really well established, or the opposite conclusion's supporters can come up with a reasonable argument for their side, the burden of proof argument will fail.

Burden shifters are a very specialized kind of counter argument. All they do is claim that the other side has set the burden of proof in the wrong place.

1. I don't have to prove that cat juggling is morally wrong. For you to assert that it is morally okay requires you to come up with an argument that shows that it is morally okay.

2. People who want us to think that some god or goddess exists have to come up with the proof. It's not our problem to prove them wrong. So if you don't have a reasonable argument to prove that your god might exist, then I can conclude that she doesn't.

The way to tell the difference between a burden of proof argument and a burden shifter is to consider whether the argument is more aimed at establishing a factual claim about the world or at establishing a logical claim about an argument. If you decide that the arguer is trying to use burden of proof to prove that some statement about the world is true, then it's a burden of proof argument. If the arguer is trying to prove that some burden of proof argument is no good, then it's a burden shifter counter argument.

Consider again Reilly's burden of proof argument against Raymond's claim that we only use ten percent of our brains.

Reilly. Raymond's claim that we only use ten percent of our brains conflicts with established background knowledge, so, since he has no credible argument, it is not true that we only use ten percent of our brains.

So long as Raymond's claim does conflict with our background knowledge, and the knowledge it conflicts with is genuinely established, the fact that he has no credible argument is itself enough to persuade us that his claim is not true. If his claim turns out not to conflict with genuinely established knowledge, then the burden of proof argument has no persuasive force.

Generally, anyone who makes a sweeping generalization or a moral claim bears the burden of proof, which means that if he fails to back up his claim with a compelling reason, we should conclude that his claim is false. Here are two examples of claims that bear the burden of proof.

Incomp says "If an organized basketball league exists then no-one can ever ride a spaceship over to the planet Mars."

Pseud says "It is immoral to wear grey socks with brown pants."

Now you might reply that these things don't seem connected to you, but Incomp and Pseud both reply that their claims are obviously true! That organized basketball just does preclude travel to Mars and grey socks with brown pants just is immoral. But no generalization is true without a reason. And if Incomp and Pseud can't back up either of their claims with reasons, then those claims are false, no matter how "obvious" they may seem. A feeling is not a reason.

Now, what if they both say "you can't prove us wrong, so we could be right!" Could it be true that organized basketball precludes travel to Mars? If it could, then you can't say it doesn't. Could it be true that it is immoral to wear grey socks with brown pants? If it could, then you can't say it isn't.

Well, I can. And I do. The point to remember is that we can prove Incomp and Pseud wrong because they bear the burden of proof here. If neither of them can come up with a reason to support his claim, then logically that claim is false. Not possibly false, just plain flat false.

If you don't think that failure to come up with a reason to support a generalization implies that that generalization is false, just remember that that also commits you to believing that the existence of organized basketball might mean we can't ever fly to Mars, and that it could be immoral to wear grey socks with brown pants, and a host of other equally ridiculous "possibilities."


Fallacies

False Burden of Proof

The false burden of proof (or "appeal to ignorance") fallacy simply assumes that because some favored statement can't be proved false, it must be true. The difference between this and a genuine burden of proof argument is that, in the fallacy, there is no established body of knowledge and no justified logical principle that shifts the burden of proof over to the other side. The purported argument rests merely on the fact that the favored claim hasn't been absolutely disproved. Since almost no significant claim about the world can be absolutely disproved, this isn't an argument. Notice however that the person committing this fallacy doesn't merely say "you haven't proved me wrong, so I can still choose to stick to my previous belief" but goes further and asserts that "you haven't proved me wrong, so you should change your mind and agree with me." Let me demonstrate.

Colt. I understand that we have no solid evidence that ancient intelligent fungi from Yoggoth are not the secret masterminds behind the explosion of New Age bookstores in this country, but you haven't proved that the Fungi from Yoggoth aren't behind the new age craze, so I'll go on believing it and you and I will have to agree to disagree on this.
Fabre. Darn right! And you have to agree that since you can't prove that crystals don't have mystical healing powers, everyone should agree that they do!

Notice that Colt doesn't claim to have proved anything. All she does is point out that the fungal mastermind theory hasn't been disproved, and so she is going to go on believing it. That's her choice to make. She doesn't expect anyone to agree with her, and doesn't claim to have offered an argument. Not so Fabre. He claims that because the healing crystal theory hasn't been disproved, we should all regard it as proved! That's pretending to have an argument, and so it's a fallacy. Here's another example.

Paulette. Christianity and Islam have about the same amount of evidence in their favor. However, people believed in Christianity before anyone believed in Islam, so Islam bears the burden of proof here.

There are two things wrong with this argument. First, the mere fact that people believe something is not enough to shift the burden of proof for an undecided observer. It's true that someone who's already a Christian is entitled to demand a high standard of proof from a Muslim who's trying to convert him, but someone who's already a Muslim is equally entitled to demand an equally high standard of proof from a prosletizing Christian. The other problem here is that, if this was a genuine argument, it wouldn't support Chritianity at all. The only religions it would support would be Pagan religions like Druidism or Odinism, or, let's face it, Neanderthal shamanism!


Irrational Proof Standard

The fallacy of irrational proof standard is basically the same thing in the other direction. Observe.

Gunther. The theory of natural selection has passed every scientific test for a theory. It has resisted all kinds of attempts at disconfirmation, and has proven to be right in a major conflict with physics. It makes correct predictions in every situation we can observe, and adequately explains every aspect of biological evolution as represented by the fossil record. Finally, it has proved to have applications outside of biology, leading to very fruitful insights, and even new sciences, in neuroscience, psychology, sociology and even computer science.
Creighton. But you still can't prove it true beyond a shadow of a doubt! In fact you can never prove absolutely that evolution happened. So obviously natural selection has not been scientifically proved!

The problem with Creighton's argument is that nothing we know about our universe is proved beyond a shadow of a doubt. The facts mentioned by Gunther actually make natural selection one of our stronger scientific theories. In some ways, Relativity and Quantum Mechanics are shakier than Natural Selection. People like Creighton usually believe many, many things on evidence far weaker than that supporting natural selection. Notice that it's not irrational for Creighton to say. "There's still some room for doubt, so I personally can choose not to believe the theory of Natural Selection." That would be his free choice. What's irrational is pretending that that extremely small room for doubt should convince other people to think that Natural Selection has not been proved to the same standard as other scientific theories.


Special Pleading

The fallacy of Special Pleading (which we've seen before) is very much like irrational proof standard and false burden of proof in that it also monkeys around with what should or shouldn't be taken as proving a case. It's a bit more complicated however, in that the arguer simultaneously claims that a particular argument or standard of proof is both good and bad. It's good when he uses it, bad when you use it. (We will see special pleading again, and again, and again.)

Elron. You should worship the true god Fnorbert, and not the false god Eki-Eki-Eki-Fatang-Fatang because the followers of Eki-Eki-Eki-Fatang-Fatang base their belief on nothing but their faith that Eki-Eki-Eki-Fatang-Fatang exists, and as we all know, faith is just another word for belief, and belief by itself proves nothing.
Princess. Well, that seems to refute Eki-Eki-Eki-Fatang-Fatang, but why should I believe in Fnorbert?
Elron. If you just have faith, then you will know for certain that Fnorbert exists.

Zoomer. We can discount professor Toohey's hypothesis because it's only 92% probable according to our available data. With professor Toohey's hypothesis out of the way, we are left with my hypothesis. My hypothesis is supported to 89% probability by the available data, which means we should accept it, since it's the only hypothesis we have left.

Stinky. The great god Vuntag determines what morality is.
Potch. How ya figure?
Stinky. Well, Vuntag can condemn us to everlasting torment, so obviously what ever she says to do is the morally right thing to do.
Potch. Well, Saddam Hussein can condemn people to years of torment, does that mean that what he says to do is the morally right thing to do?
Stinky. Of course not!
Potch. But if Saddam Hussein could condemn people to everlasting torment, that would mean that what he says to do is the morally right thing to do, wouldn't it.
Stinky. Don't be stupid. Being able to inflict everlasting torment wouldn't make Saddam Hussein determine what morality is.

If faith works for Fnorbert, it works for Eki-Eki-Eki-Fatang-Fatang. If 92% is low enough to reject professor Toohey's hypothesis, 89% is low enough to reject Zoomer's hypothesis. If the ability to inflict everlasting torment wouldn't make Saddam Hussein determine what morality is, then it wouldn't make Vuntag determine what morality is.


Finally, I want to remind you that while no-one is entitled to claim that anyone should believe something that is not supported by logic, everyone is entitled to her own opinion, whether it's logically supported or not.

Colt. I understand that we have no solid evidence that ancient intelligent Fungi from Yoggoth are not the secret masterminds behind the explosion of New Age bookstores in this country, but you haven't proved that the Fungi from Yoggoth aren't behind the new age craze, so I'll go on believing it and you and I will have to agree to disagree on this.
Fabre. Darn right! And you have to agree that since you can't prove that crystals don't have mystical healing powers, everyone should agree that they do!

This class is only about what we know, not about what we only believe. Colt can't say that she's proved that that the Fungi from Yoggoth are to blame for those new-age bookstores, but there's nothing wrong with her choosing to believe it.

Here are some exercises. As usual, the exercises denoted by letters come with answers. The ones denoted by numbers don't. Your mission is to scaefod each pair. Look for good burden of proof arguments as well as instances of false burden, irrational standard, special pleading and people getting confused between knowledge and opinion.

25. Toker. I've been smoking marijuana regularly for thirty years. I've been a stable and productive member of society all that time. I've never been in trouble, missed work, or hurt anyone. I've never driven while stoned. You haven't given me any reasons why marijuana smoking is morally wrong. In fact, all the arguments for the immorality of marijuana fail for one reason or another. So it's clearly not morally wrong to smoke marijuana.
Citlalli. Can you prove that some time in the future, maybe tomorrow, someone won't come up with a good argument? Can you prove that there's no argument out there waiting to be discovered? You can't, so it is morally wrong to smoke marijuana. (Hint)

26. Geovanni. Right now, the evidence says that there is no intelligent life in outer space. We have received no radio signals that cannot be accounted for by natural phenomena, and there is no physical evidence of any kind supporting the idea that intelligent life exists elsewhere in the universe. So the probability is that there is no intelligent life in outer space.
Katie. The trouble with that argument is that no one has ever been into outer space to look. We haven't even visited the nearest star, so you can't even prove that there's no intelligent life there. Since no one has proved that there is no intelligent life in other solar systems, it follows that there is intelligent life in some other solar system. (Answer)

27. Helen. Every argument ever offered for the existence of Vuntag has been deeply logically flawed. None of them have been the kind of argument that anyone would accept if it didn't have "Vuntag exists" as its conclusion. Since there is no remotely good argument for the existence of Vuntag, it follows logically that Vuntag doesn't exist.
Drake. Apart from the fact that none of the arguments for the existence of Vuntag are any good, you don't have any reason to think that Vuntag doesn't exist. In fact, there is no positive argument for the nonexistence of Vuntag, so it follows logically that Vuntag does exist. (Answer)
 
28. Dim Sum. We've gone over the rubble with searchers, ground penetrating radar, and search dogs. We haven't detected any movement or sound for the past three hours, so we are forced to conclude that no one is left alive in there, and we therefore should not mount a massive effort to uncover more survivors.
Satay. But you cannot prove that there is not some survivor trapped in some pocket of air somewhere in there, so we should immediately mount a massive effort and go on until we have found every survivor. (Answer)

29. Jasmyn. You keep telling me that the testimony of believers in Vuntag can be absolutely relied upon as proof of Vuntag's existence. But by that logic, the testimony of believers in Phobodisda can be absolutely relied upon as proof of Phobodisda's existence. So if Vuntag exists, so too does Phobodisda. Since they can't both exist, the rule that testimony of believers constitutes absolute proof can't work for anyone, not even Vuntag.
Efren. The trouble with that reasoning is that you are suppressing a vital piece of evidence. Vuntagian testimony can be relied upon as proof of Vuntag's existence, because it is backed by divine revelation from Vuntag, but Phobodisdan testimony cannot be relied upon as proof of the existence of Phobodisda because it is not backed by divine revelation from Vuntag. (Answer)

30. Marcelo. We've done dozens of properly controlled scientific studies, and they all show that acupuncture works at relieving pain. We've also found theoretical reasons, and independent evidence that strongly suggests that acupuncture works by stimulating the release of endorphins. No one who has applied the techniques correctly has failed to produce a relief of pain that is far superior to placebo. So now we have scientific proof that acupuncture works.
Stanley. But can you prove that acupuncture really was the mechanism that relieved the pain in every one of your studies, and in every time that acupuncture was ever applied? You can't, can you? So we don't have scientific proof that acupuncture works! (Answer)

31. Nigel. Well, I admit that no one has ever been able to get the same results that I do with the same experiment, but if we all accept my new theory, we can see that my results make sense.
Millicent. But your new theory flatly contradicts the best established theory in biological science!
Nigel. Yes, so my results justify overturning that theory.
Millicent. Not until other scientists start getting the same results you do! (Answer)

Homework. Identify the weaker argument in each dialog and critique it. That is, describe the problem with that argument with all necessary details, including the "crucial fact," and the precise way the argument goes wrong. Do this exercise on your own paper before looking at the answer sheet. Next, based on your analysis, try to figure out the exact fallacy, (Do the ezxercise on your own before looking at the answer sheet.) When you've figured out the fallacy, write a short paragraph explaining which fallacy it is, and why you think it is that particular fallacy. Once you have done both the above exercises, take a look at the Homework Answer Sheet and do the exercises there. (You will find that your previous work here will make the homework easier to do.) 1. Quinton. Judah has not produced a shred of evidence to corroborate his story of dead aliens at Roswell. Everything that was actually seen at Roswell has been fully explained for decades. He might be sincere, but he has not given anyone any reason to think that he's telling the truth. Judah. I claim, and I continue to claim that I saw dead aliens at the Roswell UFO crash site, and it is up to my critics to prove me wrong. No one has ever done so, and so it should be obvious to all of you that I'm right about this. 2. Sarina. I think we can all see that it must have been Mrs. Green. After all, Professor Plum holds a doctorate, and is a highly respected teacher, so he couldn't possibly have done it. Kelly. But Mrs. Green also holds a doctorate, and she is also a highly respected teacher! Sarina. Don't be fooled by credentials! And highly respected people have committed crimes before! No, it was her all right! 3. Zarkon. Now, your Book of Vuntag contains stories that describe events that you call "miracles." Each of these "miracles" is an event that strongly violates the laws of nature as we understand them now, and have understood them for the last thousand years. Everything we know about the way our universe works says that these "miracles" could not have happened. Since we have an absolutely enormous amount of evidence for our understanding of the laws of nature, and absolutely no evidence that they can be violated in the way that these stories say they were violated, we therefore have an extremely good argument for the conclusion that the Book of Vuntag simply isn't true. Muscatel. The problem with that argument is that the evidence for the laws of nature is only enormous. It's not perfect! It is still logically possible that our understanding of the laws of nature is incomplete, and it is logically possible that the laws were violated in exactly the way that the Book of Vuntag says they were. So you don't have any argument against the Book of Vuntag, let alone a good one.

Possible Quiz Questions (This ain't homework! Memorize the answers for next class, cuz there will be a quiz.)
1. What does "burden of proof" mean?
2. What's the difference between "knowledge" and "opinion?"
3. Who bears the burden of proof in any moral question?
4. How do burden of proof arguments work?
5. How can burden of proof arguments go wrong?
6. Explain false burden of proof.
7. Explain irrational proof standard.
8. Explain special pleading.
9. If something was believed by our ancestors, is that enough to make it knowledge?
10. Are we morally obligated to believe what our parents and grandparents believed?
11. Are we ever morally obligated to avoid evidence and logic?
12. Can a belief be “knowledge” if it is not backed up by evidence?
13. If you disagree with a person in power, do you automatically bear the burden of proof?
14. If you disagree with a religious leader, do you automatically bear the burden of proof?
15. If you disagree with the product of our best thinking so far, do you automatically bear the burden of proof?
16. If you are claiming something is morally wrong, do you automatically bear the burden of proof?
15. If you are making a definite claim, do you automatically not bear the burden of proof?
16. If something hasn’t been proved absolutely, does that mean it isn’t proved at all?
17. If a rule is valid,, does that mean it’s valid in every situation to which it can be applied?
18. Are there any logical rules that work for one person but not for someone else?

Copyright © 2006 by Martin C. Young

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