Latest_in_logic.pptx

RULES AND FALLACIES

CATEGORICAL

SYLLOGISM:

A categorical syllogism is a formal deductive argument consisting of three statements TERMS: MIDDLE TERM: It is a term that occurs in both premises and does not occur in conclusion.

THREE TERMS MAJOR TERM: Major term is the predicate of the conclusion. MINOR TERM: : Minor term is the subject of the conclusion. EXAMPLE:

No homework is fun ……… major premise Some reading is homework……… minor premise Some reading is not fun………. Conclusion

DISTRIBUTION OF TERMS: A categorical term is said to distributed if all individual members of that category are accounted. There are four categorical propositions that distribute the terms. A, E I,O are the standard names for type of state ment indicated STATEMENT TYPE

TERM DISTRIBUTED

A: All X are Y E: No X are Y I: some X are Y O: some X are not Y

subject subject, predicate none predicate

RULES AND FALLACIES: Valid syllogism conforms to certain rules which if violated, a specific “Formal Fallacy “ is committed and the syllogism becomes invalid

RULES: There are six rules for standard form of syllogisms which are presented as follows:

RULE NO: 1 RULE: A valid standard-form categorical syllogism must contain exactly three terms, each of which is used in the same sense throughout the argument. FALLACY: FALLACY OF FOUR TERMS

EXAMPLE: 1. All rare things are expensive things. All great novels are rare things. Therefore ,all great novels are expensive things. This syllogism appears to have only three terms but there are really four terms, since one of them, the middle term, is used in different senses in two pre mises. 2. All dogs are animals, All cats are mammals, So all dogs are mammals. The four terms are: dogs, animals, cats and mammals

RULE NO :2 RULE: In a valid standard form categorical syllogism the middle term must be distributed at least once.

FALLACY: Undistributed middle

EXAMPLE: All sharks are fish. All salmon are fish All salmon are sharks. In this syllogism the middle term is “fish”. In both premises “fish” occurs as the predicate of an A proposition and therefore it is not dis tributed in either premises. Thus syllogism commits the fallacy of undistributed middle.

RULE NO : 3 RULE: If a term is distributed in the conclusion, then it must be distributed in a premise.

FALLACY: Illicit major ; illicit minor

EXAMPLES: All horses are animals Some dogs are not horses Some dogs are not animals In this example there is fallacy of “illicit major.” All tigers are mammals All mammals are animals All animals are tigers In this example there is fallacy of “illicit minor.”

RULE NO :4

RULE: In a categorical syllogism, two negativ e premises are not allowed FALLACY: Exclusive premises

EXAMPLE: No fish are mammals. Some dogs are not fish. Some dogs are not mammals. This syllogism is invalid because it has two negative premises and because of that it co mmit the fallacy of exclusive premises.

RULE NO:5 RULE: A negative premise requires a negative con clusion, and a negative conclusion requires a negative premise. FALLACY: Drawing an affirmative conclusion from neg ative premise or drawing a negative conclu sion from affirmative premises.

EXAMPLE: All crows are birds Some wolves are not crows Some wolves are birds All triangles are three angled polygon All three angled polygons are three sided polygons Some three sided polygons are not triangles Both are invalid because 1st draws an affirmative con clusion from a negative premise. And 2nd draws negat ive conclusion from affirmative premises

RULE NO :6 RULE: If both premises are universal, the conclu sion cannot be particular. FALLACY: Existential fallacy.

EXAMPLE: All mammals are animals All unicorns are mammals Some unicorns are animals. This syllogism is invalid because in this cas e the conclusion is EXISTENTIAL i-e Begin ning with ‘Some’.

THANK YOU

What is a Fallacy?  Fallacies are defects that weaken arguments  Two points to remember about fallacies:  fallacious arguments are very, very common and can be quite persuasive, at least to the casual reader or listener  it is sometimes hard to evaluate whether an argument is fallacious.

Definition  Logical fallacies are flaws in reasoning that lead to faulty, illogical statements.  They are unreasonable argumentative tactics

named for what has gone wrong during the reasoning process.

The Goal  The goal today is not to label arguments as being fallacio us or fallacy-free, but help you look critically at your own arguments and strengthen them.  You should also learn to spot these fallacies in debate, an d learn how to counteract them.

Hasty Generalization Making assumptions about a whole group or range of cases based on a sample that is inadequate (usually because it is a typical or just too small).

Hasty Generalization A hasty generalization is a conclusion based on insufficient or unrepresentative evidence. Stereotyping and Sexism are forms of this fallacy. Take, for example common dumb blonde jokes:

Example "My roommate said her philosophy class was hard, and the one I'm in is hard, too. All philosophy classes must be hard! "

Tip Tip: Ask yourself what kind of "sample" you're using: Are you relying on the opinions or experien ces of just a few people, or your own experience in just a few situations? If so, consider whether you need more evidence, or perhaps a less sweeping conclusion.

Missing the Point The premises of an argument do support a particular conclu sion—but not the 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 punishment for drunk driving.”

Tip Separate your premises from your conclusion. Looking at th e premises, ask yourself what conclusion an objective perso n would reach after reading them. Looking at your conclusi on, ask yourself what kind of evidence would be required to support such a conclusion, and then see if you've actually gi ven that evidence. Missing the point often occurs when a sw eeping or extreme conclusion is being drawn, so be especiall y careful if you know you're claiming something big.

Post Hoc (False Cause) Assuming that because B comes after A, A caused B. Of c ourse, sometimes one event really does cause another one that comes later. But sometimes two events that seem related in time aren't really related as cause and event. That is, correlation isn't the same thing as causation.

Example “President Jones raised taxes, and then the rate of violent crime went up. Jones is responsible for the rise in crime.”

Tip To avoid the post hoc fallacy, the arguer would need to give us some explanation of the process by which the tax increas e is supposed to have produced higher crime rates.

Slippery Slope The arguer claims that a sort of chain reaction, usually endi ng in some dire consequence, will take place, but there's real ly not enough evidence for that assumption. The arguer asse rts 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 a ssumes we can't stop halfway down the hill.

Example “Animal experimentation reduces our respect for life. If we don't respect life, we are likely to be more and more tolerant of violent acts like war and murder. Soon our society will be come a battlefield in which everyone constantly fears for the ir lives. It will be the end of civilization. To prevent this terri ble consequence, we should make animal experimentation il legal right now.”

Tip Check your argument for chains of consequences, where yo u say "if A, then B, and if B, then C," and so forth. Make sure these chains are reasonable.

Weak Analogy Many arguments rely on an analogy between two or more o bjects, ideas, or situations. If the two things that are being co mpared aren't really alike in the relevant respects, the analo gy is a weak one, and the argument that relies on it commits the fallacy of weak analogy.

Example “Guns are like hammers—they're both tools with metal par ts that could be used to kill someone. And yet it would be ri diculous to restrict the purchase of hammers—so restriction s on purchasing guns are equally ridiculous.”

Tip Identify what properties are important to the claim you're m aking, and see whether the two things you're comparing bot h share those properties.

Appeal to Authority Often we add strength to our arguments by referring to resp ected sources or authorities and explaining their positions o n the issues we're discussing. If, however, we try to get read ers to agree with us simply by impressing them with a famo us name or by appealing to a supposed authority who really isn't much of an expert, we commit the fallacy of appeal to a uthority.

Example “We should abolish the death penalty. Many respected peo ple, such as actor Guy Handsome, have publicly stated their opposition to it.”

Tip There are two easy ways to avoid committing appeal to aut hority: First, make sure that the authorities you cite are expe rts on the subject you're discussing. Second, rather than just saying “Dr. Authority believes x, so we should believe it, t oo,” try to explain the reasoning or evidence that the autho rity used to arrive at his or her opinion. That way, your read ers have more to go on than a person’s reputation.

Ad populum The Latin name of this fallacy means “to the people.” The re are several versions of the ad populum fallacy, but what th ey all have in common is that in them, the arguer takes adva ntage of the desire most people have to be liked and to fit in with others and uses that desire to try to get the audience to accept his or her argument.

Example “Gay marriage is moral. 51% of Americans think so!”

Tip Make sure that you aren’t recommending that your audien ce believe your conclusion because everyone else believes it, all the cool people believe it, people will like you better if yo u believe it, and so forth. Keep in mind that the popular opi nion is not always the right one!

Ad hominem and tu quoq ue Like the appeal to authority and ad populum fallacies, the ad hominem (“against the person”) and tu quoque (“you, too!”) fallacies focus our attention on people rather than on argum ents or evidence.

Example “Andrea Dworkin has written several books arguing that p ornography harms women. But Dworkin is an ugly, bitter p erson, so you shouldn't listen to her.”

Example  In a tu quoque argument, the arguer points out that the op ponent has actually done the thing he or she is arguing a gainst, and so the opponent's argument shouldn't be liste ned to.

Tip Be sure to stay focused on your opponents' reasoning, rathe r than on their personal character. (The exception to this is, of course, if you are making an argument about someone's c haracter—if your conclusion is “President Clinton is an unt rustworthy person,” premises about his untrustworthy act s are relevant, not fallacious.)

Appeal to Pity The appeal to pity takes place when an arguer tries to get pe ople to accept a conclusion by making them feel sorry for so meone.

Example “I know the exam is graded based on performance, but yo u should give me an A. My cat has been sick, my car broke down, and I've had a cold, so it was really hard for me to st udy!”

Tip Make sure that you aren’t simply trying to get your audie nce to agree with you by making them feel sorry for someon e.

Appeal to Ignorance In the appeal to ignorance, the arguer basically says, “Look, there’s no conclusive evidence on the issue at hand. Theref ore, you should accept my conclusion on this issue.”

Example “People have been trying for centuries to prove that God d oes exist. But no one has yet been able to prove it. Therefore, God does not exist.” “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.”

Tip Look closely at arguments where you point out a lack of evi dence and then draw a conclusion from that lack of evidenc e.

Straw Man One way of making our own arguments stronger is to antici pate and respond in advance to the arguments that an oppo nent might make. In the straw man fallacy, the arguer sets u p a wimpy version of the opponent’s position and tries to score points by knocking it down.

Example “Feminists want to ban all pornography and punish every one who reads it! But such harsh measures are surely inappr opriate, so the feminists are wrong: porn and its readers sho uld be left in peace.”

Tip Be charitable to your opponents. State their arguments as str ongly, accurately, and sympathetically as possible. If you ca n knock down even the best version of an opponent's argum ent, then you've really accomplished something.

Red Herring Partway through an argument, the arguer goes off on a tang ent, raising a side issue that distracts the audience from wha t’s really at stake. Often, the arguer never returns to the ori ginal issue.

Example “Grading this exam on a curve would be the most fair thin g to do. After all, classes go more smoothly when the studen ts and the professor are getting along well.”

Tip Try laying your premises and conclusion out in an outline-li ke form. How many issues do you see being raised in your a rgument? Can you explain how each premise supports the c onclusion?

False Dichotomy In false dichotomy, the arguer sets up the situation so it look s like there are only two choices. The arguer then eliminates one of the choices, so it seems that we are left with only one option: the one the arguer wanted us to pick in the first plac e. But often there are really many different options, not just t wo—and if we thought about them all, we might not be so q uick to pick the one the arguer recommends!

Example “Caldwell Hall is in bad shape. Either we tear it down and put up a new building, or we continue to risk students’ saf ety. Obviously we shouldn’t risk anyone's safety, so we m ust tear the building down.”

Tip Examine your own arguments: If you’re saying that we ha ve to choose between just two options, is that really so? Or a re there other alternatives you haven't mentioned? If there a re other alternatives, don’t just ignore them—explain why they, too, should be ruled out.

Begging the Question This fallacy comes in several forms and can be harder to det ect than many of the other fallacies we've discussed. Basicall y, an argument that begs the question asks the reader to sim ply accept the conclusion without providing real evidence; the argument either relies on a premise that says the same t hing as the conclusion (which you might hear referred to as “being circular” or “circular reasoning”), or simply ign ores an important (but questionable) assumption that the ar gument rests on.

Example “Active euthanasia is morally acceptable. It is a decent, ethi cal thing to help another human being escape suffering thro ugh death.” Premise: It is a decent, ethical thing to help another human being escape suffering through death. Conclusion: Active euthanasia is morally acceptable.

Example “Murder is morally wrong. So active euthanasia is morally wrong.” The premise that gets left out is “active euthanasi a is murder.”

Tip One way to try to avoid begging the question is to write out your premises and conclusion in a short, outline-like form. S ee if you notice any gaps, any steps that are required to mov e from one premise to the next or from the premises to the c onclusion.

Equivocation Equivocation is sliding between two or more different mean ings of a single word or phrase that is important to the argu ment.

Example “Giving money to charity is the right thing to do. So chariti es have a right to our money.”

Tip Identify the most important words and phrases in your argu ment and ask yourself whether they could have more than o ne meaning. If they could, be sure you aren’t slipping and sliding between those meanings.

How Do I Find My Own Fallacies?

 Pretend you disagree with the conclusion you're defendi ng.  List your main points; under each one, list the evidence y ou have for it.  Learn which types of fallacies you're especially prone to, and be careful to check for them in your work.  Be aware that broad claims need more proof than narrow ones.  Double check your characterizations of others