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Logic 101 lecture 2


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Lecture 2 - Fallacies of Relevance

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Logic 101 lecture 2

  1. 1. Lecture 2 – Fallacies of Relevance<br />Logic 101 – Lecture 2<br />
  2. 2. Reasoning meant to convince someone of something<br />…which is not necessarily angry, impassioned, or loud<br />What is an argument?<br />
  3. 3. Deduction<br />Completely infallible proof<br />Either Obama or McCain is president.<br />McCain is not president.<br />Therefore, Obama is president.<br />Induction<br />Very veryvery likely to be true, but not necessarily true<br />Either Obama or McCain will be president.<br />Obama holds a 53% majority with 95% of precincts reporting<br />Therefore, Obama will be president.<br />Types of Logic<br />
  4. 4. Validity<br />If the premises of the argument are true, the conclusion must be true<br />If I drink the arsenic, it will kill me. Therefore, it is lethal.<br />This doesn’t care about whether or not they are ACTUALLY true<br />The arsenic is lethal whether or not I drink it<br />Soundness<br />Valid argument w/ true premises<br />What makes an argument good?<br />
  5. 5. Errors in inductive reasoning<br />May or may not be deductively true, but they are regardless invalid and not good logic<br />Lots of gray areas<br />These are patterns of reasoning that oftenfail- but these patterns may hold truth<br />It is up to you to be able to tell the difference<br />Informal Fallacies<br />
  6. 6. Arguments that fail because of a lack of connection between premises and conclusion<br />Fallacies of Relevance<br />
  7. 7. Dr. Bradshaw: “It appears that my colleague’s theory holds some weight. However, a little research shows that the theory of gravitation she is championing was first created by alchemists.”<br />AngryPundit422: “Arizona politicians say that they are trying to protect our country’s interest by checking immigration status, but is there anything more Nazi-like than saying “papers, please”?<br />Genetic Fallacy<br />
  8. 8. Attacking the (perhaps dubious) origins of an argument instead of the argument itself.<br />Nazis?<br />Alchemists?<br />(Fun fact of the day: Issac Newton was originally an alchemist- he wrote much more about alchemy than he did about physics)<br />If the argument is valid, it does not matter where it came from. Valid argument is valid.<br />Genetic Fallacy<br />
  9. 9. Anderson: “Recently, Bradshaw has argued that the theological framework expressed in the Bible was a new development in the Mediterranean area. However, a careful examination of the historical precedents shows that all of the elements of this framework had been around for centuries in various cultures around or near the Mediterranean.<br />Genetic Fallacy<br />
  10. 10. David: “Barbara would like to argue that we should stop cutting down trees in the rain forest, as it would be damaging to our environment. However, Barbara took an IQ test last week and it came up negative.”<br />Edgar: “In addition, one can easily recall that, during last election, Barbara donated $10,000 of her company’s money to the Communist party.<br />Frank: “And don’t forget that Barbara’s husband owns a large northeastern logging company, and would stand to benefit greatly if the rain forest is protected from logging operations.”<br />Ad Hominem<br />
  11. 11. Attacking the person making the argument instead of the argument itself. (Latin – “against the person”)<br />Abusive – just plain being mean<br />Associative – implying the arguer associates with unpopular or undesirable people or groups<br />Circumstantial – citing (perhaps legitimate) ulterior motives<br />Again, if the argument is valid, none of this matters. <br />Maybe it would be wise to double-check the reasoning or the data, but it doesn’t invalidate the argument.<br />Ad Hominem<br />
  12. 12. Senator Hamm: “My opponent claims that he should be elected on the basis that he is unbiased and would help to ease racial tensions in our district. However, you may recall that he was the driving force behind the resurgence of the Neo-Nazi party in last term’s election.<br />Ad Hominem<br />
  13. 13. George: “My opponent claims that I have accepted donations from lobbying groups that will influence my voting as a Congressman. However, my opponent has taken just as much, if not more, in donations from several other prominent lobbying groups.”<br />Ad Hominem TuQuoque<br />
  14. 14. Claiming the argument applies to the arguer as well (Latin – “you too”)<br />Two wrongs don’t make a right, and logic doesn’t care about hypocrisy.<br />Again, if you’re right, you’re right. Notice the pattern yet?<br />Just because you make a valid point about something doesn’t mean it negates the original argument<br />Ad Hominem TuQuoque<br />
  15. 15. Announcer: “Over 30 million people own a Chevy. Do they know something you don’t?”<br />Perry: “You should join my golf club. It’s the most exclusive in the state.”<br />Ad Populam<br />
  16. 16. Citing something’s popularity as an argument (Latin – “to the people”)<br />Band-wagoning: high popularity = good<br />Snobbery: low popularity = good<br />Incorrect logic knows no population limit (unfortunately)<br />Ad Populam<br />
  17. 17. Horace: “I’m sorry I was going 72 in a 55, officer, but I wasn’t speeding! My alarm clock didn’t go off, there was no hot water in the shower, my baby was up crying all night, and if I’m late to work one more time I’m going to get fired!”<br />Ivan: “My friend Horace here was not speeding. If you give him a ticket, you’ll make me angry, and you wouldn’t like me when I’m angry.”<br />Appeal to Pity / Force<br />
  18. 18. “Everyone has a sob story, and even if they do, it’s no excuse.” –Stephen Chbosky, The Perks of Being A Wallflower<br />Maybe the story will pull some heartstrings, but you were still breaking the law.<br />On the other hand, beating somebody up may make them let you have your way, but it sure doesn’t change the logic.<br />Appeal to Pity / Force<br />
  19. 19. Horace: “You should not give me this ticket. I am a very influential man, and I can have funding for the police department withdrawn for a very long time.”<br />This sounds like an appeal to force, but the conclusion is “you should not give me this ticket”, not that Horace wasn’t guilty of speeding. It may actually be in the officer’s best interest to let Horace off.<br />Appeal to Pity / Force<br />
  20. 20. Jules: “Some people believe the government should legalize marijuana. However, government endorsement of drug use will lead to a rapid increase in drug abuse, causing the costs of drug treatment and rehab centers to skyrocket, ultimately draining our already-strained economy.”<br />Kelly: “I wore this outfit because you told me that you liked it the last time I wore it. You didn’t notice me wearing it today. I knew it! You think I’m ugly!”<br />Straw Man<br />
  21. 21. Addressing a weaker argument that is superficially related to the argument at hand.<br />Legalizing pot is not the same thing as endorsing it<br />Wearing a nice outfit doesn’t make you attractive (or mean he was even commenting on your attractiveness)<br />Straw Man<br />