Logicalfallacies

Logicalfallacies - Transcript

Some Logical Fallacies
Fallacies are standard forms of flawed reasoning that seduce and often persuade us but that are not logically sound and will lead to faulty conclusions

Some Logical Fallacies
False Dilemma Hobson s Choice The arguer claims that there are only two options and one is unacceptable so we must accept the other However in actuality there are other alternatives




Either we ban negative ads or we let them run amok on our television stations Either the Saudis control the US government or they don t Chris Hitchens If Guns are outlawed only outlaws will have guns Daisy Girl Ad

Some Logical Fallacies
Straw man The arguer makes her own position appear stronger by misrepresenting her opponent s position




Mr Goldberg has argued against prayer in public schools Obviously Mr Goldberg advocates atheism But atheism is what they used to have in Russia Atheism leads to the suppression of all religions and the replacement of God by an omnipotent state Is that what we want for this country I hardly think so Clearly Mr Goldberg s argument is nonsense Is this really what Goldberg was arguing Almost certainly not

Some Logical Fallacies
Slippery Slope The arguer states that given a series of cases 1 2 3 n and given that the differences between each case is insignificant the difference between any two of the cases is insignificant Here the arguer fails to realize that insignificant differences when added up can make for a significant difference

Some Logical Fallacies
Slippery Slope Example Attempts to outlaw pornography threaten basic civil rights and should be summarily abandoned If pornography is outlawed censorship of newspapers and news magazines ins only a short step away After that there will be censorship of textbooks political speeches and the content of lectures by university professors Complete mind control by the central government will be the inevitable result

Some Logical Fallacies
Slippery Slope Example The government is thinking of keeping serious sex offenders behind bars to protect the public next thing we ll be keeping those convicted of manslaughter indefinitely This will inexorably lead us to a police state where the six year old who steals a piece of bubble gum will wind up in jail and society will throw away the key We cannot wait for certainty about WMD because our answer might come in the form of a mushroom cloud Condoleeza Rice

Some Logical Fallacies
Hasty Generalization Any argument that draws a generalization based on a small or unrepresentative sample size




75 of the people who responded to our Poll via e mail have some college education so 75 of all Americans have some college education You can t speak French I can t no one at FLC can

Some Logical Fallacies
Accident when a general rule is inappropriately applied to a specific case




Freedom of speech is a constitutionally guaranteed right Therefore John Q Radical should not be arrested for his speech that incited the riot last week Problematic because there are almost no absolutes Thou shalt not kill except in self defense or in service of your country etc

Some Logical Fallacies
Missing the Point


When the premise of an argument supports a particular conclusion but then a different often vaguely related conclusion is drawn
Crimes of theft and robbery have been increasing at

an alarming rate The conclusion is obvious we must reinstate the death penalty immediately

Some Logical Fallacies
Red Herring When the arguer changes the subject and take the listener down a different unrelated path


Environmentalists are continually harping about the dangers of nuclear power Unfortunately electricity is dangerous no matter where it comes from Every year hundreds of people are electrocuted by accident Since most of the accidents are caused by carelessness they could be avoided if people would just exercise greater caution

Some Logical Fallacies
Affirming the Consequent Any argument with the invalid structure of If A then B B therefore A


If I get a B on the test then I will have passed I passed the test so it follows that I must have received a B

Some Logical Fallacies
Denying the Antecedent Any argument with the invalid structure of If A then B Not A therefore not B


If it s a dog then it s a mammal It s not a dog so it must not be a mammal

Some Logical Fallacies
Equivocation The arguer shifts the meaning of a term or phrase from one premise to the next






Insane people are considered not responsible for their actions Your poor driving habits show a serious lack of responsibility so you must be insane Every society is of course repressive to some extent as Sigmund Freud pointed out repression is the price we pay for civilization That kid s a little terror I hope he doesn t fly planes into buildings some day

Some Logical Fallacies
Begging the Question The arguer supports the conclusion simply by restating it as a premise or by leaving out a key premise






I know she loves me because she told me so and you don t lie to someone you love God exists because the Bible says that he does We all know that the Bible is accurate because it was written by inspired men men inspired by God to write down his words Whatever is less dense than water will float because such objects won t sink in water Murder is morally wrong This being the case it follows that abortion is morally wrong

Some Logical Fallacies
Appeals to force fear The arguer tries to get you to accept their view on the grounds that you will be harmed if you don t They use attempt to motivate you from fear rather than logically persuade you




So you re an animal rights activist I d consider changing my views if I were you because most of us here on the prairies are beef farmers and we don t care too much for your kind Willie Horton Ad

Some Logical Fallacies
Appeals to pity Ad Misericordium The arguer tries to get you to accept their view on the grounds that they will be harmed if you don t




I really need you to give me an A in this course I know I didn t do that well but an average grade will bring my grade point average down Just do as I ask before you give me a heart attack

Some Logical Fallacies
Prejudicial language The arguer uses biased language either positive or negative to support their views rather than offering evidence


We should offer our support to Haiti because they are a backward nation and thus require guidance from a progressive country like ours

More Prejudicial Language
Revenue Enhancement taxes protective reaction strike or air support bombing pre dawn tactical insertion early morning invasion incontinent ordinance Off target bombs friendly fire Shelling friendly village or troops mistakenly Human Remains Pouches Body Bags flexible coffins Strategic Withdrawal retreat selective ordinance or selected chemical insertion napalm Involuntary conversion of an aircraft plane crash Eastern Airlines public safety unit in some countries a murder squad Collateral damage dead innocent civilians

Some Logical Fallacies
Faulty appeal to authority The arguer appeals to an authority who s area of expertise is irrelevant to the issue at hand or appeals to a person who is famous but not an expert




Madonna is against animal testing So animal testing is probably an unethical practice Noted psychologist Dr Frasier Crane recommends that you buy the EZ Rest Hot Tub

Some Logical Fallacies
Fallacy of Exclusion
Important evidence which would undermine an argument is excluded from consideration The requirement that all relevant information be included is called the principle of total evidence

Jones is a Coloradoan and most Coloradoans vote Republican so Jones will probably vote Republican The information left out is that Jones lives in Durango and that most people in Durango vote Democrat The Rockies will probably win this game because they ve won nine out of their last ten Eight of the Rockies wins came over last place teams and today they are playing the first place team

Some Logical Fallacies
Confusions of Part and Whole
A Composition Fallacy Because the parts of a whole have a certain property it is argued that the whole has that property Conventional bombs did more damage in W W II than nuclear bombs Thus a conventional bomb is more dangerous than a nuclear bomb B Ecological Fallacy Because the whole has a certain property it is argued that the parts have that property Jews vote Democratic So Ismael must also vote Democratic



Some Logical Fallacies
Ad hominem attack Poisoning the well The arguer suggests that her opponent s view is unacceptable because of some negative character trait Attack the person rather than the argument




People who say that hazing in the military is wrong are just a bunch of wimps He s a liar so there s no reason to listen to him But Ginsberg s arguments are nothing but trash Ginsberg was a marijuana smoking homosexual and a thoroughgoing advocate of the drug culture Humphrey Ad

Some Logical Fallacies
Ad hominem circumstantial The arguer suggests that her opponent s view is false because the opponent has something personal to gain if it is accepted


Of course France opposed the war on Iraq they ve got millions of dollars of contracts at stake We should disregard that scientist s argument because they are being funded by the logging industry

Some Logical Fallacies
Ad hominem tu quoque You too The arguer suggests that her opponent s position is inconsistent with their own beliefs or actions and therefore the position is false




You re telling me to stop speeding on the highway You ve received more speeding tickets than I have Gore is a hypocrite on Campaign finance issues he s raised as much money as anyone You say I shouldn t drink but you haven t been sober for more than a year

Some Logical Fallacies
Guilt by Association The arguer suggests her opponent s views should be rejected because the opponent is a member of a perceived disreputable group or the views of the opponent are also held by persons of a disreputable group






Nationalized health care programs are unacceptable because they are the sort of thing that Communists support There s no reason to deal with Arafat He s a known terrorist Politician X once spoke with the leader of the KKK

Some Logical Fallacies
Appeal to numbers popularity The arguer appeals to the sheer number of persons who agree with the belief or to the popularity of the belief as evidence that it is true


Because a majority of Americans believe in UFO s they must exist That many people can t be wrong 4 out of 5 dentists recommend brushing with pure cane sugar

Some Logical Fallacies
Appeal to vanity


Tying an idea to a popular person or value
The few the proud the marines Be all you can be

Appeal to snobbery


If you qualify as one of the select few this distinguished car can be seen and driven at

Some Logical Fallacies
Two wrongs make a right The arguer appeals to consistency stating that a wrong action belief should be accepted on the basis that another similar wrong action belief was accepted


Joe shouldn t be prosecuted for that crime Many other people do it and get away with it Who care s about Clinton s affairs All the other presidents have done it

Some Logical Fallacies
Appeal to Ignorance
The arguer uses the fact that a proposition has not been disproven as evidence that the proposition is true or if it has not been proven that it is false








People have been trying for centuries to provide conclusive evidence that astrology doesn t work But they haven t Therefore we must conclude that the claims of astrology are true You haven t disproven that Mossad wasn t involved in 9 11 which suggests they almost surely were Since you cannot prove that ghosts do not exist they probably exist Since scientists cannot prove that global warming will occur it probably won t

Some Logical Fallacies
Appeal to Tradition The arguer bases the acceptance of a position on the mere fact that they have always believed it or that it has always been accepted that it is true


Although horrendous in our eyes the burning of the wives of deceased men should be considered morally acceptable since the society in question has been doing it for centuries

Some Logical Fallacies
Post hoc ergo proctor hoc after this therefore because of this The arguer uses the fact that one thing happened before another as evidence that the first thing caused the second thing


Ever since we repainted the house I ve been overly tired it must mean I m allergic to the paint Let s not take Bill on our picnic every time we take him it rains The quality of education in our schools has been declining for years Clearly our teachers aren t doing their jobs

Some Logical Fallacies
Dicto simipliciter argument based on an unqualified generalization


exercise is good everyone should exercise

Some Logical Fallacies
False Analogy comparing situations that are different




Students should look at textbooks during exams because lawyers have briefs If we can put a man on the moon we should be able to eliminate poverty His Her ideas sound a lot like what we saw in Nazi Germany

Some Logical Fallacies
Hypothesis Contrary to the Fact start with a hypothesis that s not true and draw conclusions from it


If Columbus had never found America the Islanders would not have been decimated by disease
But someone else would have later

Some Logical Fallacies
Definition too broad The definition includes items that should not be included




An apple is something that is red and round The planet Mars is red and round So it is included in the definition But obviously it is not an apple A figure is square if and only if it has four sides of equal length Not only squares have four sides of equal length trapezoids do as well

Some Logical Fallacies
Definition too narrow The definition does not include items which should be included




An apple is something that is red and round Golden Delicious are apples however they are not red They are not included in the definition however they should be Something is music if and only if it is played on a piano A drum solo cannot be played on a piano yet it is still considered music

Some Logical Fallacies
Complex Question Two otherwise unrelated points are illegitimately conjoined and treated as a single proposition The reader is expected to accept or reject both together when in reality they should be considered separately




You should support home education and the God given right of parents to raise their children according to their own beliefs Do you support freedom and the right to bear arms Have you stopped shoplifting This asks two questions did you shoplift and did you stop

Examples
Doby Gillis


What is the main lesson we should draw from Doby Gillis

Resources
Hurley Patrick J A Concise Introduction to Logic Wadsworth http www datanation com fallacies index htm

http www kcmetro cc mo us longview ctac fallacy examples in political ads