Logical-Fallacies逻辑谬论优质PPT.ppt

1、Making assumptions about a whole group or range of cases based on a sample that is inadequate（usually because it is atypical or just too small）.Stereotypes about people（frat boys are drunkards,grad students are nerdy,etc.）are a common example of the principle underlying hasty generalization.Example:

2、My roommate said her philosophy class was hard,and the one Im in is hard,too.All philosophy classes must be hard!Two peoples experiences are,in this case,not enough on which to base a conclusion.,Missing the Point,Definition:The premises of an argument do support a particular conclusion-but not the

3、conclusion that the arguer actually draws.Example:The seriousness of a punishment should match the seriousness of the crime.Right now,the punishment for drunk driving may simply be a fine.But drunk driving is a very serious crime that can kill innocent people.So the death penalty should be the punis

4、hment for drunk driving.The argument actually supports several conclusions-The punishment for drunk driving should be very serious,in particular-but it doesnt support the claim that the death penalty,specifically,is warranted.,Post hoc（false cause）,This fallacy gets its name from the Latin phrase po

5、st hoc,ergo propter hoc,which translates as after this,therefore because of this.Definition:Assuming that because B comes after A,A caused B.Of course,sometimes one event really does cause another one that comes later-for example,if I register for a class,and my name later appears on the roll,its tr

6、ue that the first event caused the one that came later.But sometimes two events that seem related in time arent really related as cause and event.That is,correlation isnt the same thing as causation.Examples:President Jones raised taxes,and then the rate of violent crime went up.Jones is responsible

7、 for the rise in crime.“The increase in taxes might or might not be one factor in the rising crime rates,but the argument hasnt shown us that one caused the other.,Slippery Slope,Definition:The arguer claims that a sort of chain reaction,usually ending in some dire consequence,will take place,but th

8、eres really not enough evidence for that assumption.The arguer asserts that if we take even one step onto the slippery slope,we will end up sliding all the way to the bottom;he or she assumes we cant stop halfway down the hill.Example:Animal experimentation reduces our respect for life.If we dont re

9、spect life,we are likely to be more and more tolerant of violent acts like war and murder.Soon our society will become a battlefield in which everyone constantly fears for their lives.It will be the end of civilization.To prevent this terrible consequence,we should make animal experimentation illega

10、l right now.Since animal experimentation has been legal for some time and civilization has not yet ended,it seems particularly clear that this chain of events wont necessarily take place.,Also known as“the Camels Nose,Weak Analogy,Definition:Many arguments rely on an analogy between two or more obje

11、cts,ideas,or situations.If the two things that are being compared arent really alike in the relevant respects,the analogy is a weak one,and the argument that relies on it commits the fallacy of weak analogy.Example:Guns are like hammers-theyre both tools with metal parts that could be used to kill s

12、omeone.And yet it would be ridiculous to restrict the purchase of hammers-so restrictions on purchasing guns are equally ridiculous.While guns and hammers do share certain features,these features（having metal parts,being tools,and being potentially useful for violence）are not the ones at stake in de

13、ciding whether to restrict guns.Rather,we restrict guns because they can easily be used to kill large numbers of people at a distance.This is a feature hammers do not share-itd be hard to kill a crowd with a hammer.Thus,the analogy is weak,and so is the argument based on it.If you think about it,you

14、 can make an analogy of some kind between almost any two things in the world:My paper is like a mud puddle because they both get bigger when it rains（I work more when Im stuck inside）and theyre both kind of murky.So the mere fact that you draw an analogy between two things doesnt prove much,by itsel

15、f.,Appeal to Authority,Definition:Often we add strength to our arguments by referring to respected sources or authorities and explaining their positions on the issues were discussing.If,however,we try to get readers to agree with us simply by impressing them with a famous name or by appealing to a s

16、upposed authority who really isnt much of an expert,we commit the fallacy of appeal to authority.Example:We should abolish the death penalty.Many respected people,such as actor Guy Handsome,have publicly stated their opposition to it.While Guy Handsome may be an authority on matters having to do wit

17、h acting,theres no particular reason why anyone should be moved by his political opinions-he is probably no more of an authority on the death penalty than the person writing the paper.,Appeal to Pity,Definition:The appeal to pity takes place when an arguer tries to get people to accept a conclusion

18、by making them feel sorry for someone.Example:I know the exam is graded based on performance,but you should give me an A.My cat has been sick,my car broke down,and Ive had a cold,so it was really hard for me to study!The conclusion here is You should give me an A.But the criteria for getting an A ha

19、ve to do with learning and applying the material from the course;the principle the arguer wants us to accept（people who have a hard week deserve As）is clearly unacceptable.Example:Its wrong to tax corporations-think of all the money they give to charity,and of the costs they already pay to run their

20、 businesses!,Appeal to Ignorance,Definition:In the appeal to ignorance,the arguer basically says,Look,theres no conclusive evidence on the issue at hand.Therefore,you should accept my conclusion on this issue.Example:People have been trying for centuries to prove that God exists.But no one has yet b

21、een able to prove it.Therefore,God does not exist.Heres an opposing argument that commits the same fallacy:People have been trying for years to prove that God does not exist.But no one has yet been able to prove it.Therefore,God exists.In each case,the arguer tries to use the lack of evidence as sup

22、port for a positive claim about the truth of a conclusion.There is one situation in which doing this is not fallacious:If qualified researchers have used well-thought-out methods to search for something for a long time,they havent found it,and its the kind of thing people ought to be able to find,th

23、en the fact that they havent found it constitutes some evidence that it doesnt exist.,Straw Man,Definition:One way of making our own arguments stronger is to anticipate and respond in advance to the arguments that an opponent might make.The arguer sets up a wimpy version of the opponents position an

24、d tries to score point by knocking it down.Example:Feminists want to ban all pornography and punish everyone who reads it!But such harsh measures are surely inappropriate,so the feminists are wrong:porn and its readers should be left in peace.The feminist argument is made weak by being overstated-in

25、 fact,most feminists do not propose an outright ban on porn or any punishment for those who merely read it;often,they propose some restrictions on things like child porn,or propose to allow people who are hurt by porn to sue publishers and producers,not readers,for damages.,Red Herring,Definition:Pa

26、rtway through an argument,the arguer goes off on a tangent,raising a side issue that distracts the audience from whats really at stake.Often,the arguer never returns to the original issue.Example:Grading this exam on a curve would be the most fair thing to do.After all,classes go more smoothly when

27、the students and the professor are getting along well.Lets try our premise-conclusion outlining to see whats wrong with this argument:Premise:Classes go more smoothly when the students and the professor are getting along well.Conclusion:Grading this exam on a curve would be the most fair thing to do

28、.When we lay it out this way,its pretty obvious that the arguer went off on a tangent-the fact that something helps people get along doesnt necessarily make it more fair;fairness and justice sometimes require us to do things that cause conflict.But the audience may feel like the issue of teachers an

29、d students agreeing is important and be distracted from the fact that the arguer has not given any evidence as to why a curve would be fair.,False Dichotomy,Definition:In false dichotomy,the arguer sets up the situation so it looks like there are only two choices.The arguer then eliminates one of th

30、e choices,so it seems that we are left with only one option:the one the arguer wanted us to pick in the first place.Example:Caldwell Hall is in bad shape.Either we tear it down and put up a new building,or we continue to risk students safety.Obviously we shouldnt risk anyones safety,so we must tear

31、the building down.The argument neglects to mention the possibility that we might repair the building or find some way to protect students from the risks in question-for example,if only a few rooms are in bad shape,perhaps we shouldnt hold classes in those rooms.,Begging the Question,Definition:A complicate