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Logical Fallacies (for debate and persuasive writing)

Well, here is the branch off fallacy thread. Hopefully this will help you to avoid some common logical mistakes that can stick out in your writing like a sore thumb. I will present a few common fallacies and what they entail. Please add more! Also, I'm no expert so feel free to correct any misconceptions that I have about the following.

Straw Man: This is a common mistake (or sometimes it is done on purpose as a cheap argumental trick) where one party will misinterpret or misrepresent the opposing party's argument and then disprove or counter the new warped version of said argument. It is called straw man because it is is easier to break down a straw man than a real one. Likewise it is easier to break down a cheap or false imitation of an argument that the real argument itself. An example:

Kevin: I think it is a real possibility that consciousness came before form.

Potential Fallacious Debater: So you are saying that some big old man in the sky created earth? That's ridiculous!

False Dilemma: This is done when a debater presents two choices as if they are the "only choices" that can be possibly made in a situation. In reality there are other routes a person could take or other reasons for a particular event's occurrence, etc. besides the two that are presented by the false dilemma. Example:

President Bush: You're either with us, or you're with the terrorists.
(A person could easily appose terrorism and the Bush administration's offensive realist strategies at the same time. No, I don't mean "offensive" as in irritating or angering.)

Ad Hominem: This is the most annoying of fallacies in my opinion. It occurs when one party will personally attack the other party as a way to discredit their argument. In meaningful debate arguments should be analyzed from an unbiased standpoint. Martin Luther King Jr.'s I Have A Dream speech comes to mind here. (One day arguments will not be judged by the personal situation of the arguer but by the content of it's premises!) Personal issues from a debater's life may be relevant in establishing credibility but hold no bearing on the validity of any logical argument. If facts are supposed to be taken on faith from an arguing party then perhaps their credibility should be examined, but this would still hold no sway over the examination of the soundness of his/her logic. Logical examinations can be done without taking information on faith and are either evidently sound or not. Personal issues cannot change the logical validity of an argument, even if the arguer is completely hypocritical of his/her points. Example:

John: Since humans and animals share many basic instincts, they should have certain equal rights.

Homer: Well, you're a vegetarian! So, of course you want animal rights.

Red Herring: This is one of the easiest fallacies to spot. (Though, not in every case, of course.) It occurs when one party introduces a completely new or unrelated idea into an argument or discussion in order to distract from a certain opposing point that they are unable to counter. This is obviously not productive for the debate at all since instead of trying to meet an opponent's arguments with logical arguments a person will simply change the subject. Example:

Kathleen: Steven, I think you should take the garbage out today because I have taken it out every night for the past week! I think you should contribute around the house more.

Steven: That's great, honey, but I just wanted to let you know that I found a nest of raccoons in the attic this morning and I think we really should call someone about that right away because they could cause some serious structural damage to this house we just bought together. You know I am only thinking of the best for you, dear.

Well, there are plenty of other fallacies out there and the ones I presented aren't defined in the best of possible terms so feel free to add to and revise what I have here!

This is very interesting! I have to admit that I haven't learned anything about logical fallacies yet. Is the concept usually taught in English? Speech? Philosophy? I feel like I am pretty good at recognizing fallacies, but I don't have the vocabulary to name them. Can I give you examples of a couple of situations and have you help me identify what kind logical fallacies they would represent?

The first one would be when someone tells you that they are "a third Cherokee Indian" or that their dog is "99% wolf." Well, now I happen to know that there are two parents, four grandparents, eight great grandparents, sixteen . . . thirty-two . . . sixty-four. Those numbers really don't add up to being a "third" of anything and proving a dog is 99% wolf would be difficult at best.

The other one was the proclamation that Thomas Jefferson had fathered children with his slave Sally Hemmings because there was "DNA proof." The DNA tests did show a relationship between the decedents of Thomas Jefferson and some of the decedents of Sally Hemmings, but wouldn't that be expected? Hemmings' mother had belonged to Jefferson's wife's family and Sally was purportedly the offspring of Jefferson's father-in-law . . . making Martha Jefferson and Sally Hemmings half sisters. Even if you were able to use more sophisticated tests that tested only traits handed down through the male line, you wouldn't be able to exclude Jefferson's brother (who many contemporaries believed to be the father of some of Sally Hemmings' children-her offspring were fathered by both black and white men), Jefferson's nephews, or any number of other Jefferson males with common ancestors. What kind of fallacy would it be to simply state, "DNA proves Thomas Jefferson fathered children with slave mistress" or something of the sort?

Thank you for starting this thread (and the critical thinking thread). I am looking forward to learning more.
Jun 1, 2009   #3
Hmmm . . . Tyler, you have used the word "appose" when you meant to say "oppose." Clearly nothing you have to say on the issue of logical fallacies is correct.

Sorry, I couldn't resist :-)

This is an excellent thread, and you are to be commended for starting it. Your list of fallacies and your explanations of them are wonderful in every way, apart from your misuse of "appose."

Other fallacies:

The argument from authority: This occurs when the person arguing attempts to substitutes names of prominent supporters of a position in place of actual arguments. An example taken from another thread:

Nick94: "Scientists like Dr. Lee Spetner and Dr. Werner Gitt agree that mutation has never added information to the genetic code."

Look at those big "Dr."s! And in case you missed it, they're scientists! Of course, that these two people have degrees and agree on the truth of a statement does not make that statement actually true. In this case, it's doubly misleading, as there are far more "Dr."s out there, over 90% of scientists in biology, who disagree with them. More to the point, even if they had numbers on their side, the truth of an argument does not hinge upon popular support for it. At best, pointing out that over 90% of scientists believe that mutation can add to the genetic code is only a good reason for suggesting that someone go out and read the arguments those scientists have made. It should not be a substitute for those arguments, or used to refute objections to them.

Post Hoc, Ergo Propter Hoc (After this, therefore because of this): This argument mistakes correlation for causation. Causation is very, very difficult to prove, and correlation is very, very easy to notice, so this error comes up a lot.

Example: After guns were banned in 1990, violent crime dropped 5% from 1991-1995. Clearly, banning guns lowers crime rates.

Not really. The crime rate may have been going down for years before guns were banned, in which case the trend would merely have continued unchanged. If the crime rate had been dropping at a rate of 2% a year from 1985-1990, the statistics could even be taken as evidence that banning guns increases crime rates, though that would probably be to make a similar mistake in the other direction. More likely, there are a host of other factors that would have to be controlled for before one could make any assertion about the effects of gun control on crime.

The slippery slope argument: Also very common, this one is often used, quite sincerely and earnestly, by people who should know better. It consists of saying, essentially, that while X might be all right on its own, it might lead to Y, which would be unacceptable.

Example: Euthanasia for the terminally ill who request it may not seem so bad, but allowing this practice would eventually lead to families killing off elderly relatives whose health care costs are too high with the blessings of the medical establishment.

Letting people get away with murder under the pretense of carrying out euthanasia would be bad. This in no way addresses the question of whether genuinely euthanizing the terminally ill is good. In essence, it is a form of straw man argument, in that the arguer is substituting Y, which is much easier to argue against, for X, the thing that is actually being debated.

Well, this post is getting a tad long, so I'll leave it there for now. As to Eric's question, what you are describing isn't a fallacy so much as a lie. Such claims often rely on people's scientific ignorance combined with an argument from authority (DNA proves it, and everyone knows that DNA evidence is irrefutable). Statistics are often abused in this way, because so many people nowadays are largely innumerate. To educate yourself against this sort of statistical abuse, I recommend reading any or all of the works of John Allen Paulos.
Jun 1, 2009   #4
I'm so glad to see this thread. I'll add one now and more another day.

Appeal to Faulty Authority. Claiming or citing expertise or authority that seems valid but, upon reflection, is dubious or invalid. "As a breast cancer survivor, I can tell you that [some form of treatment] doesn't work." An oncologist would be a reliable authority on the efficacy, or lack thereof, of various treatments. A breast cancer survivor knows what it's like to have breast cancer, and might even know that a particular treatment didn't work in her case, but merely having a disease doesn't automatically make you an expert on that disease and its treatment.

Real world example: Relatives of 9-11 victims testify before Congress about what should be done to combat terrorism. Of course, those who have lost family members to terrorism know that terrorism is a grave danger and have the right to call for more to be done. But losing a brother or uncle to a terrorist attack doesn't make one an expert on the respective efficacy of different ways of fighting terrorism.

And of course, the most common example of all: "because I said so and I'm your mother."

Notoman, in answer to your question, this is usually taught in philosophy, cursorily in introductory courses and then more thoroughly in logic. But the best composition textbooks and teachers include instruction on fallacies, so that their students learn to recognize and avoid them.
Jun 2, 2009   #5
And some more:

The sharpshooter effect: I don't know if this is a logical fallacy per se, so much as a dishonest research technique, but I feel it has a place here. In essence, this involves drawing grids that give you the results you want. It is much like shooting at a barn 100 times, then drawing a bullseye around the area with the highest concentration of bullets. Anyone who didn't know you had drawn the target after taking the shots might think you were a great sharpshooter.

Example: many studies about the dangers of nuclear power plants or electromagnetic fields suffer from this fallacy. For instance, in one study purporting to prove that electromagnetic fields caused cancer, researchers showed a grid drawn over a small town. Each square of the grid was then analyzed to see how much electromagnetic activity existed in the area, and how high the incidence of cancer was. Sure enough, the two or three areas with the highest EM activity also had the highest cancer rates. The research captured headlines around the world. However, other scientists were not so sure. They wondered if maybe the town had been chosen precisely because it was reporting a higher than usual rate of cancer, and if the researchers hadn't further drawn the grids where they thought they saw patterns. It turns out that, when the grid was extended across the entire state (using the original grid as a starting point), then on average, squares with higher than average EM fields tended, on average, to have lower cancer rates than normal, "proving" that EM fields protected against cancer. As it turned out, even drawing another grid over the original town, this time picking a random starting point, eliminated the correlation shown on the first grid. All the research had proved is that, if you pick a place where cancer rates are higher than normal (as some places will be, just by random chance) and then draw a grid that clusters them with EM producing power lines, then you can create exactly the result you are looking for.

argumentum ad misericordiam (appeal to pity): This is a variant on the appeal to emotion. One can appeal to fear, anger, or other emotions just as easily.

Example: Children are suffering in Africa. They are so young, and vulnerable, yet they sit there with flies landing on swollen lips as they clutch their protruding, malnourished bellies in hunger. We should send aid to their governments.

Perhaps we should. Then again, it might be that the governments in question will merely siphon the aid money into buying weapons to wage war against their neighbors, or that the aid will in fact reach the children, saving them, and allowing them to reproduce so that in twenty years their are twice as many starving children, and only half as many willing donors. The conclusion in the example is in no way supported by the description of the children, though of course it may actually be valid.

Example 2 (Appeal to anger): All of the hijackers on 9/11 were Saudi Arabian. We must declare war on Saudi Arabia.

That all of the hijackers were from Saudi Arabia does not mean that the Saudi government supported the attack, or that war with Saudi Arabia would serve America's interests. As in the previous example, the conclusion might be right, but the fact given in support of it does not in and of itself constitute logical proof of it.
Jun 2, 2009   #6
Non Sequitor (it does not follow). Drawing a conclusion that does not logically follow from the premises. Sean's example of an appeal to anger above is also a non sequitor. That war should be declared on Saudi Arabia does not logically follow from the fact that the hijackers were Saudi Arabian.
Jun 2, 2009   #7
Simpson's paradox: This one is difficult for me to explain. Essentially, though, it involves an aggregate trend showing the reverse of either all or the majority of the trends it contains. Hopefully the example below will make my meaning clearer. If not, wikipedia might: en.wikipedia.org/wiki/Simpson%27s_paradox

Example: The most famous case involves the University of California, Berkeley, which was sued in 1973 for discriminating against women. The evidence seemed clear -- the university had admitted 44% of male applicants, and only 35% of female applicants. However, the university successfully defended itself by pointing out that, on a department by department basis, it had clearly discriminated, in the majority of the cases, against men (which, unlike discrimination against women, was apparently perfectly fine). And even the two departments that had admitted a higher percentage of male than female applicants had admitted more women than men (owing to their being a much higher number of female than male applicants).

The apparent paradox arises only if one assumes that men and women are the same and will therefore apply to each department in equal numbers, and that the departments themselves are the same size, and therefore accept roughly the same number of students. In such a case, it would be impossible for each department to discriminate against men, yet for the university to end up seeming to discriminate against women. However, this is not the case. For example, one department had 108 female applicants and 825 male applicants. It admitted 89 women (82% of of them) and 512 men (only 62% of them). Another department had 191 male applicants and 393 female applicants. This department actually did show a very small bias towards men. It admitted 53 men (28% of them) and 94 women (24% of them). However, if the university had consisted of only these two departments, then it would have admitted 565 of 1016 men (55.6%), and 183 of 501 women (36.5%). Thus, it would seem as if the university were heavily biased against women, when in fact one of the departments was showing a 20% bias for women, and the other only a 4% bias against them.

In fact, if it had admitted only women where possible, letting in all 108 candidates for the one department, and 147 for the other (leaving 493 male acceptances in one and 0 in the other), the university would only have just broken even (255 of 501 female candidates yielding a 51% overall acceptance rate, and 493 of 1016 male candidates yielding a 49% overall acceptance rate). It is easy to imagine a scenario in which even accepting all female candidates where possible would still leave the university in the position of seeming to discriminate against women. Even in this example, it would have taken only about twenty fewer female applicants to the first department to get such a result.
Jun 2, 2009   #8
Fallacy of Composition: Attributing the same traits that are exhibited by certain members of a group onto the entire group as a whole. Example:

Premise 1: Biological Cells are invisible to the naked eye.
Premise 2: The human body is made of cells.
Conclusion: The human body is invisible.

Fallacy of Division: Attributing the same traits that are exhibited by a group as a whole onto individual members of that group. Example:

Premise 1: A paragraph in a newspaper offers newsworthy information.
Premise 2: A paragraph in a newspaper is made up of individual words.
Conclusion: An individual word offers newsworthy information.

Masked Man Fallacy: The assumption that two elements cannot be the same if the extent of certain knowledge possessed by a party about each individual element is different. Example:

Premise 1: I know Jeff.
Premise 2: I don't know who stole the banana.
Conclusion: Jeff and the banana stealer cannot be the same person.
Jun 2, 2009   #9
Here's a big one:

Equivocation: Using a word in two or more different senses in the same argument.

Example: Nothing is better than playing video games. Watching television is better than doing nothing. Ergo, watching television is better than playing video games.

The use of the word "nothing" is different in the two premises, and so cannot support the conclusion.

Equivocation also has a series of broader meanings, as discussed here: web.uvic.ca/psyc/bavelas/1988politic.pdf
Jun 2, 2009   #10
Begging the Question: Framing the question so that what needs to be proved is assumed or, in other words, assuming that which has to be proved.

It drives me crazy, by the way, when people say "that begs the question..." when what they mean is "that raises the question." Immediately, that tells me that the speaker or writer is not well-educated enough to know what "beg the question" really means or is just too sloppy to care.
Jun 2, 2009   #11
Ah yes, we call such horribly uneducated people "Americans." After all, if one consults an American dictionary such as Merriam-Webster, one finds the following:

"1: to pass over or ignore a question by assuming it to be established or settled
2: to elicit a question logically as a reaction or response <the quarterback's injury begs the question of who will start in his place>"

So, in America, someone who uses the phrase "begging the question" in the sense you describe, is not in fact wrong, working from the premise that anyone who uses a word or phrase in a given sense may reasonably claim to be right if he shows that his usage is sanctioned by his country's main dictionary.

My personal favorite, though, is that "macaber" is now given as a correct pronunciation of "macabre" in the same dictionary. It sure is easier for a country to update its dictionary than to educate its people :-)
Certainly, public consensus on the common usage of words, will impact what becomes accepted.

Though you might justify it with your buddies, it won't fly if you're an academic, or professional.

As long as that boundary is hard to surmount, I don't see how it's a problem.

Why would you care that some ordinary person who doesn't know better, is butchering the language, when it remains preserved in its original form among scholars and the upper echelon of society?

They'll ammend the dictionary to note that a word has taken on a new spelling or meaning with a lot of people, but you'll hardly find a learned person who won't repudiate them.
They'll ammend the dictionary to note that a word has taken on a new spelling or meaning with a lot of people, but you'll hardly find a learned person who won't repudiate them.

I am finding more and more amended entries in the dictionary. Forte/forte is an interesting one. It is pronounced "fawr-tey" if you are using it as a musical term. If you are saying that something is your strength, then the word should be pronounced pronounced like "fort." It presents a quandary! Do you say "fawr-tey" because it is the common usage or do you risk people thinking you are stupid when you say "fort"? Or do you avoid the word altogether in speech like I do?

Decimate is another word I avoid using. Its original usage meant to kill or destroy one in every ten (hence the "deci"), but it is commonly used as "total or near destruction" more recently. The word has lost its meaning for me. One in ten is a lot different than total destruction.
Jun 12, 2009   #14
Hence my original point. Once a word usage has been officially accepted into the dictionary, it is just that, official. Insisting on the original usage at that point is mere snobbery, even among the upper echelon of society. My complaint wasn't about the process per se -- that's how languages evolve, but about the speed with which Americans engage in it. The pace of change in a language should be kept as slow as possible. The faster a language changes in one area of the world, the sooner it will become incomprehensible to people in another part of it who would otherwise still share a common tongue.

Btw, no one will think you are stupid if you pronounce it "fawrtey," given that the pronunciation is now considered standard (though the original is still acceptable too). Likewise, the notion that decimating something involves destroying a tenth of it is well on its way to being obsolete, so using it in its common sense is perfectly fine.
It's not snobbery Sean, because you won't get far in life or be taken seriously with a casual mentality to introduce malapropisms in your work.

I would challenge you to find me a dissertation that has "common use" words.

Find me a professional who is affected by the malleability of words among laypeople.

You've preempted a ceiling on yourself if you can't be precise and accurate, forget with words, but any kind of research.
Jun 12, 2009   #16
But words aren't malapropisms, or indeed any other form of mis-usage, if they are being used as they are defined. So, once a usage has become common enough that the dictionary lists it as a standard meaning, then that is in fact a correct way to use the word, quite literally by definition. If a usage is still listed as "non-standard," as is the case with "irregardless," then you can rightfully look down your nose at people who use it with some justification. Otherwise, you're just being a stuffy old (or in some cases young) snob.

In any event, this thread is getting off-topic. So, a logical fallacy:

The Loaded Question (also known as the Fallacy of Complex Questions or the Fallacy of Many Questions): This fallacy involves condensing two or more questions into one, so that any answer signals acceptance of a premise that may be disagreed with.

Example: Have you stopped torturing small animals yet?

Either a "yes" or a "no" answer involves accepting the premise that you have, at some time, tortured small animals.
Yes, this a great thread. If you can avoid fallacies, and train yourself to recognize them where they appear, you'll save yourself a lot of time.

Hmmmm, since I'm taking stats, I thought I should include:

The Gambler's Fallacy

Suppose you've tossed a coin 10 times and it has come up tails each time; you reason, "well, the odds are with me, heads is due soon."

Unfortunately, if you're betting on heads (or tails), the probability of winning is no greater than 50% since coin tosses are independent of each other -- the coin has no memory, so your previous bad luck doesn't have any bearing whatsoever on the next toss.

Gamblers, many times in casinos after a string of bad luck, reason that there is a sway for things to turn around.

It can be a costly fallacy, literally.
Jun 12, 2009   #18
Note that in such cases, the odds may actually lie in other direction. True randomness is hard to come by. If something that is supposed to be random seems to favor a particular result, it may well be that the device itself is flawed in a way that means it does actually favor that result. Obviously not that applicable to coin tosses. Nor should one bet large sums of money on this being the case in any particular situation.
Ad hominem tu quoque

Even if someone's actions are grossly inconsistent with what they say, what they're saying shouldn't be diminshed by it.

Let's say Joe is a flamboyant homosexual, but he is strongly opposed to gay marriage on the grounds that it is wrong as ordained by God.

Joe is a poor representative of that view, quite probably because his actions don't reflect what he preaches, but homosexuality isn't any less wrong; Joe saying it, shouldn't diminish whatever truth there is in it.
Jun 13, 2009   #20
If you believe in cause and effect then you must understand that there is nothing random in the physical universe. (Unless you go back to the big bang or something of that nature. I will accept that that may be the exception but we do not know for sure.) Even computers can't do random. They operate on a system that is so complex and has so many variables that to a human it seems random but in reality it is just a really complicated system. Randomity is just an illusion created by humans who are do not possess enough brain power to take into account every variable that can affect a certain event. Even dice rolling is not random. If you had a brain powerfull enough to calculate every single variable that comes into play when you roll dice you could predict the result every time. Since we are not smart enough to predict such things we say that the result is "random" even though there is no such thing.
Jun 13, 2009   #21
Or unless you start studying quantum theory, which describes the world as essentially, fundamentally random at its very roots. Of course, many scientists believe that variables will one day be discovered that will restore a deterministic cause and effect worldview, but that hasn't happened yet.
Jun 13, 2009   #22
start studying quantum theory, which describes the world as essentially, fundamentally random at its very roots

--- could you give a citation for this please !
Jun 14, 2009   #23
Certainly. Search Google Books for "randomness quantum theory." It is mentioned on p.474 of this text, for instance: books.google.ca/books?id=88U6hdUi6D0C&pg=PA474&dq=ran domness+quantum+theory

I think that's a side point, though, in that text. This one books.google.ca/books?id=pwrBp3ZGaUYC&pg=PA2&dq=rando mness+quantum+theory&client=firefox-a seems to go into it more directly.

The nature of randomness in quantum physics is hotly debated, but everyone agrees that it appears random. Whether it really is, or whether this appearance is an illusion created by our lack of understanding of as yet undiscovered variables, is much less clear, though.

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