Slide 12: Appeal to IgnoranceAppeal to Ignorance…Appeal to Ignorance…3: False AlternativesFalse Alternatives…False Alternatives4: Loaded Question5: Questionable CauseQuestionable Cause: post hoc fallacyQuestionable Cause: mere correlation fallacyQuestionable Cause: oversimplified cause fallacy6: Hasty Generalization7: Slippery SlopeSlippery Slope Examples8: Weak AnalogyWeak Analogy ContinuedWeak Analogy ContinuedWeak Analogy Continued9: InconsistencySlide 21Summary For QuizSummarySummaryFor Next TimeCritical ReasoningWeek 7: Class 22: Appeal to IgnoranceWhen we lack evidence for or against a claim, it is usually best to suspend judgment—to admit that we just don’t know. the fallacy of appeal to ignorance occurs when an arguer asserts that a claim must be true because no one has proven it false or, conversely, that a claim must be false because no one has proven it true. There must be intelligent life on other planets. No one has proven that there isn’t. There isn’t any intelligent life on other planets. No one has proven that there is.Appeal to Ignorance…First exception, sometimes the fact that a search hasn’t found something is good evidence that the thing isn’t there to be found. Here are two examples:We’ve searched this car from top to bottom looking for the stolen jewels, and no trace of them has been found. Therefore, probably the jewels aren’t in the car.It is important to keep in mind, however, that this “fruitless search” exception applies only when (1) a careful search has been conducted and (2) it is likely that the search would have found something if there had been anything there to be found.Appeal to Ignorance…Second exception, cases in which special rules require that a claim be rejected as false unless a certain burden of proof is met. In the American legal system, a criminal defendant is legally guilty only if his or her guilt is proved beyond a reasonable doubt. My client has not been proven guilty beyond a reasonable doubt. Therefore, my client is not legally guilty.In this example, special rules of evidence require that a claim be rejected as false unless it is proven to be true by some elevated standard of proof. Because these special rules justify the inference “not proven, therefore false,” no fallacy is committed.3: False Alternativeswhen an arguer poses a false either/or choiceEither we elect a Republican as president, or crime rates will skyrocket. Obviously, we don’t want crime rates to skyrocket. Therefore, we should elect a Republican as president.Note that the fallacy of false alternatives need not involve just two false choices. There are just three types of base hits in baseball: a single, a double, and a triple. Slugger got a base hit but didn’t get a single or a double. Therefore, Slugger must have gotten a triple.False Alternatives…Often, a false choice is expressed as a conditional (if-then) statement:If we don’t elect a Democrat as president, then the economy will go down the tubes. Obviously, we don’t want the economy to go down the tubes. So, we should elect a Democrat as president.False AlternativesFinally, it should be noted that fallacies of false alternatives are often expressed as incomplete arguments. Here are two examples:Either buy me some candy, Daddy, or I’ll hold my breath until I die.Dad, I know a new BMW is expensive, but you wouldn’t want me riding around in this old rust bucket all winter long, would you?What are the missing parts of these arguments?4: Loaded Questionoccurs when an arguer asks a question that contains an unfair or unwarranted presupposition. Have you stopped beating your wife?To respond to a loaded question effectively, one must distinguish the different questions being asked and respond to each individually. Strictly speaking, a loaded question is fallacious only if it is used unfairly in an argumentative context.5: Questionable CauseWhen an arguer claims, without sufficient evidence, that one thing is the cause of something else.There are three common varieties of the questionable cause fallacy: the post hoc fallacy, the mere correlation fallacy, and the oversimplified cause fallacy.Questionable Cause: post hoc fallacypost hoc ergo propter hoc [“after this, therefore because of this”when an arguer assumes, without adequate evidence, that because one event, A, occurred before another event, B, A is the cause of B. How do I know that ginseng tea is a cure for the common cold? Last week I had a bad case of the sniffles. I drank a cup of ginseng tea, and the next morning my sniffles were gone.Medieval villager: Two days after that old hag Jezebel Taylor moved into the village, my cow died. That witch must have put a hex on my cow!Questionable Cause: mere correlation fallacyWhen an arguer assumes, without sufficient evidence, that because A and B regularly occur together, A must be the cause of B or vice versa. Correlation does not imply causation!On Monday I stayed up all night partying, had eggs for breakfast, and failed my calculus test. On Wednesday I stayed up all night partying, had eggs for breakfast, and failed my biology test. On Thursday I stayed up all night partying, had eggs for breakfast, and failed my history test. Obviously, to do better on tests, I must stop eating eggs for breakfast.Aztec high priest: Every spring we sacrifice a virgin to the sun god, and every summer the life-giving rains come. Therefore, sacrificing a virgin to the sun god causes the life-giving rains to come.Questionable Cause: oversimplified cause fallacywhen we assume, without adequate evidence, that A is the sole cause of B when, in fact, there are several causes of B. Violent crime has declined steadily in recent years. Obviously, tougher imprisonment policies are working.SAT scores have fallen sharply since the 1960s. Clearly, students are watching too much TV.6: Hasty GeneralizationA generalization is a statement that asserts that all or most things of a certain kind have a certain quality or characteristic: All emeralds are green.We commit the fallacy of hasty generalization when we draw a general conclusion from a sample that is biased or too small. Do most Americans still believe in God? To find out, we asked more than ten thousand scientists at colleges and universities throughout America. Less than 40 percent said they believed in God. The