Presentation is loading. Please wait.

Presentation is loading. Please wait.

Chapter 4 Logical Fallacies.

Similar presentations

Presentation on theme: "Chapter 4 Logical Fallacies."— Presentation transcript:

1 Chapter 4 Logical Fallacies

2 Logical Fallacies 1. A fallacy is an error in reasoning—a type of argument that may seem to be correct, but proves not to be so upon closer examination. An argument is said to commit a fallacy when it makes a mistake of a given type. There are four main categories of logical fallacies: (1)fallacies of relevance, (2) defective induction, (3)presumption, and (4)ambiguity. Within these four subcategories, this chapter covers 17 different logical fallacies.

3 Logical Fallacies Fallacies of relevance rely on premises that seem to be relevant to the conclusion when, in fact, they are not. There are six major fallacies of relevance: 1. Appeals to emotion 2. Red herring 3. Straw man 4. Argument ad hominem 5. Appeal to force 6. Missing the point (irrelevant conclusion)

4 Appeals to Emotion Also called ad populum (to the populace)
The most obvious of all fallacies Yet also the most common error made It appeals to the emotions of the audience It is used by advertising, politicians, propaganda The speaker relies on expressive language and other devices to excite the audience for their cause or against another – rather than to use rational argument and evidence Choice of words that cause an emotive response Also ad misercordiam – appeal to pity or mercy

5 Examples Appeal to emotion
"Pornography must be banned. It is violence against women." "For thousands of years people have believed in Jesus and the Bible. This belief has had a great impact on their lives. What more evidence do you need that Jesus was the Son of God? Are you trying to tell those people that they are all mistaken fools?"

6 Red herring The fallacy that relies on distraction
Attention is deflected away from the topic being argued or discussed and focused on another area that is related to the topic (or not) but irrelevant to the point being argued Any deliberately misleading trail is called a red herring ure=related

7 Red herring example This fallacy is committed when someone introduces irrelevant material to the issue being discussed, so that everyone's attention is diverted away from the points made, towards a different conclusion. "You may claim that the death penalty is an ineffective deterrent against crime--but what about the victims of crime? How do you think surviving family members feel when they see the man who murdered their son kept in prison at their expense? Is it right that they should pay for their son's murderer to be fed and housed?"

8 Straw Man Arguing the opponent’s view as one that is easily torn apart (made of straw) It is similar to red herring in that it distracts from the real argument by placing words or entire arguments that were never made or said Key words for this : all, every, none, never and of course… “the man” (the government, big brother, etc) YouTube - The "Straw Man" Fallacy

9 Straw man example The straw man fallacy is when you misrepresent someone else's position so that it can be attacked more easily, knock down that misrepresented position, then conclude that the original position has been demolished. It's a fallacy because it fails to deal with the actual arguments that have been made. "To be an atheist, you have to believe with absolute certainty that there is no God. In order to convince yourself with absolute certainty, you must examine all the Universe and all the places where God could possibly be. Since you obviously haven't, your position is indefensible."

10 Argument against the person
Also called ad hominem (to the man) The most irrational and morally wrong of the fallacies Often hurtful and attempting personal damage of the person The argument shifts away from the topic and becomes an attack on the person instead Two major types : abusive and circumstantial Abusive – attempts to disparage the character of the other directly; insult Circumstantial – attacking what a person does, or did, or their affiliation, etc.

11 Person example Argumentum ad hominem literally means "argument directed at the man"; there are two varieties. The first is the abusive form. If you refuse to accept a statement, and justify your refusal by criticizing the person who made the statement, then you are guilty of abusive argumentum ad hominem. For example: "You claim that atheists can be moral--yet I happen to know that you abandoned your wife and children." This is a fallacy because the truth of an assertion doesn't depend on the virtues of the person asserting it. A less blatant argumentum ad hominem is to reject a proposition based on the fact that it was also asserted by some other easily criticized person. For example: "Therefore we should close down the church? Hitler and Stalin would have agreed with you." A second form of argumentum ad hominem is to try and persuade someone to accept a statement you make, by referring to that person's particular circumstances. For example: "Therefore it is perfectly acceptable to kill animals for food. I hope you won't argue otherwise, given that you're quite happy to wear leather shoes." This is known as circumstantial argumentum ad hominem. The fallacy can also be used as an excuse to reject a particular conclusion. For example: "Of course you'd argue that positive discrimination is a bad thing. You're white." This particular form of Argumentum ad Hominem, when you allege that someone is rationalizing a conclusion for selfish reasons, is also known as "poisoning the well."

12 Appeal to Force Also called ad baculum (to the stick)
Using threats or strong arm methods to win the argument rather than to discuss it

13 Force examples An Appeal to Force happens when someone resorts to force (or the threat of force) to try and push others to accept a conclusion. This fallacy is often used by politicians, and can be summarized as "might makes right." The threat doesn't have to come directly from the person arguing. For example: "Thus there is ample proof of the truth of the Bible. All those who refuse to accept that truth will burn in Hell." "In any case, I know your phone number and I know where you live. Have I mentioned I am licensed to carry concealed weapons?"

14 Missing the Point Also called ignoratio elenchi (mistaken refutation)
This happens when an argument goes off track, a disconnect occurs somewhere along the way and the ‘point is missed’ Usually the cause of faulty logic and poor rationing ability Frequently occurs when one does not understand the proposition in dispute Exercises p.135 – 141

15 Elenchi basic example The fallacy of Irrelevant Conclusion consists of claiming that an argument supports a particular conclusion when it is actually logically nothing to do with that conclusion. For example, a Christian may begin by saying that he will argue that the teachings of Christianity are undoubtedly true. If he then argues at length that Christianity is of great help to many people, no matter how well he argues he will not have shown that Christian teachings are true. Sadly, these kinds of irrelevant arguments are often successful, because they make people to view the supposed conclusion in a more favorable light.

16 Logical Fallacies Fallacies of defective induction arise from the fact that the premises of the argument, although relevant to the conclusion, are so weak and ineffective that reliance upon them is a blunder. We will cover these 4 major ones: 1. Arguments from ignorance 2. The appeal to inappropriate authority 3. False cause 4. Hasty generalization/converse accident

17 Arguments from ignorance
Also called ad ignorantium (to ignorance) If something is not proven true, then it must be false That we are ignorant to the truth , means it must be false An informal fallacy in which a conclusion is supported by an illegitimate appeal to ignorance (lack of knowing as true), as when it is supposed that something is likely to be true because we cannot prove it is false

18 Ad ignorantium examples
Argumentum ad ignorantiam means "argument from ignorance." The fallacy occurs when it's argued that something must be true, simply because it hasn't been proved false. Or, equivalently, when it is argued that something must be false because it hasn't been proved true. (Note that this isn't the same as assuming something is false until it has been proved true. In law, for example, you're generally assumed innocent until proven guilty.) Here are a couple of examples: "Of course the Bible is true. Nobody can prove otherwise." "Of course telepathy and other psychic phenomena do not exist. Nobody has shown any proof that they are real." In scientific investigation, if it is known that an event would produce certain evidence of its having occurred, the absence of such evidence can validly be used to infer that the event didn't occur. It does not prove it with certainty, however. For example: "A flood as described in the Bible would require an enormous volume of water to be present on the earth. The earth doesn't have a tenth as much water, even if we count that which is frozen into ice at the poles. Therefore no such flood occurred." It is, of course, possible that some unknown process occurred to remove the water. Good science would then demand a plausible testable theory to explain how it vanished.

19 Appeal to inappropriate authority
Also called ad verecundiam ( to the respected one) Using the example of an expert or an authority figure (mom, priest, teacher) to prove your argument is valid An informal fallacy in which the appeal to authority is illegitimate because the authority appealed to has no special claim to expertise on the matter in question ature=related

20 Appeal to inappropriate authority
The Appeal to Authority uses admiration of a famous person to try and win support for an assertion. For example: "Isaac Newton was a genius and he believed in God." This line of argument isn't always completely bogus when used in an inductive argument; for example, it may be relevant to refer to a widely- regarded authority in a particular field, if you're discussing that subject. For example, we can distinguish quite clearly between: "Hawking has concluded that black holes give off radiation" and "Penrose has concluded that it is impossible to build an intelligent computer" Hawking is a physicist, and so we can reasonably expect his opinions on black hole radiation to be informed. Penrose is a mathematician, so it is questionable whether he is well-qualified to speak on the subject of machine intelligence.

21 False Cause Also called non causa pro causa (non cause for cause)
Attempting to link a cause and effect relationship that is not really there An informal fallacy in which the mistake arises from accepting as the cause of an event what is not really the cause A variety of this is the post hoc ergo hoc (after the thing, therefore because of the thing) – just because something happened does not mean it caused another thing that may be unrelated to it A0ED907098&playnext=1&index=13

22 Causa example The fallacy of Non Causa Pro Causa occurs when something is identified as the cause of an event, but it has not actually been shown to be the cause. For example: "I took an aspirin and prayed to God, and my headache disappeared. So God cured me of the headache.“ The fallacy of Post Hoc Ergo Propter Hoc occurs when something is assumed to be the cause of an event merely because it happened before that event. For example: "The Soviet Union collapsed after instituting state atheism. Therefore we must avoid atheism for the same reasons.“ related

23 Hasty Generalization When we draw conclusions all persons or things in a given class on the basis of our knowledge of one or a few The informal fallacy in which a principle that is true of a particular case is applied, carelessly or deliberately, to the majority of other cases ure=related g5GY&feature=fvw

24 Hasty generalizations
Bill: "You know, those feminists all hate men." Joe: "Really?" Bill: "Yeah. I was in my philosophy class the other day and that Rachel chick gave a presentation." Joe: "Which Rachel?" Bill: "You know her. She's the one that runs that feminist group over at the Women's Center. She said that men are all sexist pigs. I asked her why she believed this and she said that her last few boyfriends were real sexist pigs. " Joe: "That doesn't sound like a good reason to believe that all of us are pigs." Bill: "That was what I said." Joe: "What did she say?" Bill: "She said that she had seen enough of men to know we are all pigs. She obviously hates all men." Joe: "So you think all feminists are like her?" Bill: "Sure. They all hate men."

25 Logical Fallacies Fallacies of presumption arise when an argument relies on a proposition that is assumed to be true, but is in fact false, dubious, or without warrant. There are three such fallacies: 1. Accident 2. Complex question 3. Begging the question

26 Accident Moving from a generalization to a specific
An informal fallacy in which a generalization is applied to individual cases that it does not govern (not related to)

27 Accident samples A sweeping generalization occurs when a general rule is applied to a particular situation, but the features of that particular situation mean the rule is inapplicable. It's the error made when you go from the general to the specific. For example: "Christians generally dislike atheists. You are a Christian, so you must dislike atheists." This fallacy is often committed by people who try to decide moral and legal questions by mechanically applying general rules.

28 Complex Question Rhetorical questions that include the conclusion/answer already in them An informal fallacy in which a question is asked in such a way as to presuppose the truth of some proposition buried in the question itself

29 Complex question examples
One example is the classic loaded question: "Have you stopped beating your wife?" The question presupposes a definite answer to another question which has not even been asked. This trick is often used by lawyers in cross-examination, when they ask questions like: "Where did you hide the money you stole?" Similarly, politicians often ask loaded questions such as: "How long will this EU interference in our affairs be allowed to continue?" or "Does the Chancellor plan two more years of ruinous privatization?" Another form of this fallacy is to ask for an explanation of something which is untrue or not yet established.

30 Begging the question Also called petitio principii (assuming the initial point) The proof of the argument is in its own point An informal fallacy in which the conclusion of an argument is stated or assumed in one of the premises Exer. P

31 Begging the question examp
This fallacy occurs when the premises are at least as questionable as the conclusion reached. Typically the premises of the argument implicitly assume the result which the argument purports to prove, in a disguised form. For example: "The Bible is the word of God. The word of God cannot be doubted, and the Bible states that the Bible is true. Therefore the Bible must be true. "Homosexuals must not be allowed to hold government office. Hence any government official who is revealed to be a homosexual will lose his job. Therefore homosexuals will do anything to hide their secret, and will be open to blackmail. Therefore homosexuals cannot be allowed to hold government office."

32 Logical Fallacies Fallacies of ambiguity (called sophisms)occur when arguments are formulated such that they rely on shifts in the meaning of words from their premises to their conclusions. Such ambiguous language results in five fallacies of ambiguity: 1. Equivocation 2. Amphiboly 3. Accent 4. Composition 5. Division

33 Equivocation Using words other meanings intentionally to distort an argument An informal fallacy in which two or more meanings of the same word or phrase have been confused intentionally or accidentally

34 Equivocation examples
Equivocation occurs when a key word is used with two or more different meanings in the same argument. For example: "What could be more affordable than free software? But to make sure that it remains free, that users can do what they like with it, we must place a license on it to make sure that will always be freely redistributable." One way to avoid this fallacy is to choose your terminology carefully before beginning the argument, and avoid words like "free" which have many meanings.

35 Amphiboly Ambiguous premises because of grammatical issues
An informal fallacy arising from the loose, awkward, or mistaken way in which words are combined, leading to alternative possible meanings of a statement. ture=related

36 Amphiboly examples Amphiboly occurs when the premises used in an argument are ambiguous because of careless or ungrammatical phrasing. For example: "Premise: Belief in God fills a much-needed gap." Furnished Apartments for Rent: 3 rooms, river view, private phone, bath, kitchen, utilities included Your interest is aroused. But when you visit the apartment, there is neither a bathroom nor a kitchen. You challenge the landlord. He remarks that there are common bathroom and kitchen facilities at the end of the hall. 'But what about the private bath and kitchen that the ad mentioned?' you query. 'What are you talking about?' the landlord replies. 'The ad didn't say anything about a private bath or a private kitchen. All the ad said was private phone.' The advertisement was amphibolous

37 Accent Changing the emphasis on certain words or phrases to distort the meaning An informal fallacy committed when a term or phrase has a meaning in the conclusion of an argument different from its meaning in one of the premises, the difference arising chiefly from a change in emphasis given to the words used.

38 Accent examples Accent is a form of fallacy through shifting meaning. In this case, the meaning is changed by altering which parts of a statement are emphasized. For example: "We should not speak ill of our friends" and Be particularly wary of this fallacy on the net, where it's easy to misread the emphasis of what's written.

39 Composition Two types:
(1) Reasoning fallaciously from the attributes of the parts of a whole to the attributes of the whole itself – because a part means or is one thing then the whole thing exhibits those same qualities (2) Reasoning from attributes of the individual elements or members of a collection to attributes of the collection or totality of those elements – because elements/members have an attribute the whole thing/membership has the same issue. An informal fallacy in which an inference is mistakenly drawn from the attributes of the parts of a whole to the attributes of the whole itself.

40 Composition examples The Fallacy of Composition is to conclude that a property shared by a number of individual items, is also shared by a collection of those items; or that a property of the parts of an object, must also be a property of the whole thing. Examples: "The bicycle is made entirely of low mass components, and is therefore very lightweight." "A car uses less petrochemicals and causes less pollution than a bus. Therefore cars are less environmentally damaging than buses." A related form of fallacy of composition is the "just" fallacy, or fallacy of mediocrity. This is the fallacy that assumes that any given member of a set must be limited to the attributes that are held in common with all the other members of the set. Example: "Humans are just animals, so we should not concern ourselves with justice; we should just obey the law of the jungle." Here the fallacy is to reason that because we are animals, we can have only properties which animals have; that nothing can distinguish us as a special case.

41 Division Two types: (1) Arguing fallaciously that what is true of a whole must also be true of its parts - because something is true of a whole then it is true with all that whole’s parts (2) When one argues from the attributes of a collection of elements to the attributes and elements themselves – the collection is given the same value of its individual elements An informal fallacy in which a mistaken inference is drawn from the attributes of a whole to the attributes of the parts of that whole. zM&feature=related Exer. P

42 Division examples The fallacy of division is the opposite of the fallacy of composition. It consists of assuming that a property of some thing must apply to its parts; or that a property of a collection of items is shared by each item. "You are studying at a rich college. Therefore you must be rich." "Ants can destroy a tree. Therefore this ant can destroy a tree."

43 Slippery Slope ature=related

44 Discussion 1. What do the fallacies of relevance have in common? Choose three of them and discuss how, though they are distinct, they share this common thread. 2. Why are ad hominem arguments usually made? Are such arguments ever valid? Explain. 3. How does the argument ad populum differ from just using emotive language to persuade? 4. One of the most common logical fallacies is that of begging the question. Think of some examples of this fallacy, and discuss how they assume what they seek to prove. 5. The fallacy of accent is common in advertising. Take some examples of advertisements from the media and identify examples of this fallacy, showing how they suggest their misleading misinterpretations.

45 Essays 1. What are the distinctions between fallacies of accent, equivocation, and amphiboly? Using examples of each, explain how these fallacies are distinct. 2. What do the fallacies of false cause and accident have in common? Are they really the same fallacy, are they entirely distinct, or are they related in some, but not all ways? Explain your answer by giving an example of each. 3. At first glance, composition and division may seem to be the same as accident and converse accident. However, they are entirely different. Explain what the real difference is between these pairs of fallacies.

46 Essays continued. 4. Is arousing emotional responses in an argument always a fallacy? For example, some charities use stirring appeals to rouse our pity. Are such arguments the fallacy of “appeal to pity?”What about references to prestigious individuals, such as well-known experts— aren’t those passages cases of “appeal to inappropriate authority?” Be sure to use examples to back up your essay’s claims. 5. Examine the following passage for fallacies, and write an essay describing any fallacious reasoning you detect in it: “Some people say the reasons to transplant organs, such as the heart and liver, from one human to another are obvious. However, I don’t think so. People have vastly different religious and cultural beliefs, and may attribute spiritual significance to certain organs. Terrible psychological damage could occur, for instance, if a person were to receive the heart of a person regarded in that culture as having bad moral character. Moreover, there are other psychological problems to consider. In the case of ovary transplants, any woman willing to subject herself to this dangerous procedure must have an abnormal desire to produce children from her own body. Should society contribute to these psychological problems by allowing organ transplants?”

Download ppt "Chapter 4 Logical Fallacies."

Similar presentations

Ads by Google