Reason Continued


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Continuation of Miss Mott-Thornton's ToK presentation on Reason

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Reason Continued

  1. 1. Reason Continued…
  2. 2. Recap types of logic: <ul><li>Deductive Logic </li></ul><ul><li>Reasoning from the general to particular </li></ul><ul><li>Example: </li></ul><ul><ul><li>all metals expand when heated. </li></ul></ul><ul><ul><li>A is a metal </li></ul></ul><ul><ul><li>Therefore A expands when heated </li></ul></ul><ul><li>Its more certain but less informative than induction </li></ul><ul><li>Inductive logic </li></ul><ul><li>Reasoning from the particular to the general </li></ul><ul><li>Example: </li></ul><ul><ul><li>Metal A expands when heated </li></ul></ul><ul><ul><li>Metal B expands when heated </li></ul></ul><ul><ul><li>Metal C expands when heated </li></ul></ul><ul><ul><li>Therefore all metals expand when heated </li></ul></ul><ul><li>Its more informative, but less certain than deduction </li></ul>
  3. 3. The relationship between reasoning and certainty <ul><li>What percentage of the metal existing on our planet would you guess scientists have tested to see if it expands when heated? </li></ul><ul><li>What does this tell you about the certainty or otherwise of scientific laws? </li></ul>
  4. 5. What distinguishes good and bad generalisations? <ul><li>Number – you should look at a reasonable amount of instances </li></ul><ul><li>Variety - You should look at a variety of instances </li></ul><ul><li>Exceptions – You should actively look for counter examples. This will help to guard against a confirmation bias. </li></ul><ul><li>Coherence – you should demand more evidence to support surprising claims than to support unsurprising ones. </li></ul><ul><li>It would take more to convince me that there is life on Mars than to convince me that there is life in the school pond. </li></ul><ul><li>Subject Area – generalisations are more reliable in some subjects than in others </li></ul>
  5. 6. Logic as a pathway to truth <ul><li>We have seen that reason provides a way of laying out information, in a way that sometimes helps us get closer to truth. </li></ul><ul><li>When using deductive reasoning one must be able to answer ‘yes’ to both of the following questions: </li></ul><ul><li>Are the premises true? </li></ul><ul><li>Is the argument valid? </li></ul>
  6. 7. Logic as a pathway to truth <ul><li>Premise 1) some Monks are Tibetans </li></ul><ul><li>Premise 2) All Tibetans are good at yoga </li></ul><ul><li>Therefore, </li></ul><ul><li>Conclusion: some monks are good at Yoga </li></ul><ul><li>Are the premises true? </li></ul><ul><li>Is the argument valid? </li></ul><ul><li>..some evidence of Tibetans who are good at Yoga </li></ul><ul><li>So Premise 2) is possibly true </li></ul>
  7. 8. Preserving truth <ul><li>So, although we can’t be 100% certain of the truth of the 2 nd premise, unless we find evidence from every Tibetan, </li></ul><ul><li>And unless we have reason to believe that Tibetan monks generally shun yoga, </li></ul><ul><li>Although the argument is not strictly valid, </li></ul><ul><li>We can tentatively accept the truth of the conclusion. </li></ul><ul><li>This is because the scope of the claim could be fairly small . </li></ul><ul><li>We don’t need to find many Tibetan Monks who are good at Yoga for the conclusion to be true . </li></ul>
  8. 9. Filling in the premises to an argument <ul><li>When people argue in everyday life, they rarely set their arguments out in a formal way. </li></ul><ul><li>If the speaker regards one of the premises as obvious, they may simply imply or assume that these are true, without stating them explicitly as a premises. </li></ul><ul><li>Therefore, you will sometimes have to fill in the premises to someone else’s argument, if you want it to make logical sense . </li></ul>
  9. 10. Fill in the missing premise: <ul><li>1) Lucy goes to Oxford University </li></ul><ul><li>2) Oxford only takes very intelligent students </li></ul><ul><li>Therefore: Lucy must be very intelligent. </li></ul><ul><li>1) Graham is a politician </li></ul><ul><li>2) All politicians are probably lying. </li></ul><ul><li>Therefore: Graham is probably lying </li></ul>
  10. 11. Fill in the missing premise: <ul><li>1) Cheerleaders compete, train, and have a high level of physical fitness. </li></ul><ul><li>2) All Olympic events involve competing, training and having a high level of physical fitness. </li></ul><ul><li>Therefore: Cheerleading should be an Olympic event </li></ul><ul><li>1)it is natural to eat meat </li></ul><ul><li>2) There is never anything morally wrong with anything natural </li></ul><ul><li>Therefore: There is nothing morally wrong with eating meat. </li></ul>
  11. 12. Using Venn diagrams
  12. 13. Venn diagrams help you work out if a syllogism or argument is valid <ul><li>It is sometimes difficult to work out if a syllogism is true or false. </li></ul><ul><li>One way of working out what is going on is to draw a Venn diagram. Consider the following syllogism: </li></ul><ul><ul><li>1) all As are Bs. </li></ul></ul><ul><ul><li>2) some As are Cs. </li></ul></ul><ul><ul><li>Therefore: some Bs are Cs. </li></ul></ul><ul><li>To work out if this is valid or not, represent the groups of things which are As inside the group of things which are Bs ... </li></ul>
  13. 14. Using Venn diagrams <ul><li>...and to represent ‘ some As are Cs’ have the circle of Cs intersect the circle of As. </li></ul><ul><li>So it follows that ‘ somes Bs are Cs’ </li></ul><ul><li>the argument is valid. </li></ul>B A C
  14. 15. Task: <ul><li>Can you use the following venn diagram to make a syllogism? </li></ul>
  15. 18. Fallacies Types of invalid reasoning
  16. 19. Types of Fallacy <ul><li>The types of Fallacy we’ll focus on: </li></ul><ul><li>Post hoc ergo propter hoc </li></ul><ul><li>Ad Hominem Fallacy </li></ul><ul><li>Circular reasoning </li></ul><ul><li>Equivocation </li></ul><ul><li>False Dilemma </li></ul>
  17. 20. Fallacies <ul><li>Post hoc ergo propter hoc </li></ul><ul><li>Meaning: ‘ after this, therefore on account of this’ </li></ul><ul><li>consists of assuming that because one thing, B , follows from another thing, A , then A must be the cause of B . eg: </li></ul><ul><ul><li>1) at 6pm the girls ate tomato soup </li></ul></ul><ul><ul><li>2) at 7pm the girls committed murders </li></ul></ul><ul><ul><li>Therefore: tomato soup causes girls to murder </li></ul></ul>
  18. 21. Fallacies <ul><li>Ad Hominem </li></ul><ul><li>Meaning: ‘ against the man’ </li></ul><ul><li>consists of attacking or supporting a person rather than the argument itself . eg: </li></ul><ul><ul><li>Raffles told me to vote conservative at the next election </li></ul></ul><ul><ul><li>Raffles would say that because he is a conservative counsellor </li></ul></ul><ul><li>Although the ad hominem fallacy is committed mostly by criticising someone, it can also be committed by supporting them. </li></ul><ul><li>If I said ‘Martin Luther King jr was a Christian, so Christianity must be true ’ </li></ul><ul><li>Then I am again focusing on the speaker rather than the argument. </li></ul>
  19. 22. fallacies <ul><li>Circular reasoning </li></ul><ul><li>Aka ‘ begging the question ’ </li></ul><ul><li>Consists in assuming the truth of the thing you are supposed to be proving . Eg: </li></ul><ul><ul><li>“ I know that Jesus was the Son of God because he said he was, and the Son of God would not lie.” </li></ul></ul><ul><li>this is not an argument, but a reassertion of original position, with no appeal to reasons. </li></ul><ul><li>Anthony Flew’s example: </li></ul><ul><li>‘ Three thieves are arguing about how to divide up 7 pearls they have stolen. </li></ul><ul><li>One picks up the pearls and gives two to each of the other two, keeping three for himself. </li></ul><ul><li>“ I get more because I’m the leader” </li></ul><ul><li>“ how come your the leader?” </li></ul><ul><li>“ because I’ve got more pearls.” </li></ul>
  20. 24. fallacies <ul><li>Equivocation </li></ul><ul><li>This occurs when a word is used in two different senses in an argument. </li></ul><ul><ul><li>1) a hamburger is better than nothing </li></ul></ul><ul><ul><li>2) Nothing is better than good heath </li></ul></ul><ul><ul><li>Therefore: a hamburger is better than good health. </li></ul></ul><ul><li>This appears formally valid, because the premises follow from the conclusion. </li></ul><ul><li>But there is something wrong with it. </li></ul><ul><li>The problem lies with the word ‘nothing’ because it has a different meaning in each of the premises . </li></ul><ul><li>In the 1 st premise it means ‘not having anything ’ </li></ul><ul><li>In the 2 nd it means ‘there is not anything’ </li></ul><ul><li>Maybe this is why many argument s end up being about the meanings of words. </li></ul>
  21. 26. Fallacies <ul><li>False Dilemma </li></ul><ul><li>This is the fallacy of assuming that there are only two alternatives , when there are in fact a wider range of options. Eg: </li></ul><ul><li>‘ Do those who advocate an increase in military expenditure want to see schools and hospitals close?’ </li></ul><ul><li>They imply that we only have two choices: </li></ul><ul><li>Either we increase military expenditure </li></ul><ul><li>Or we keep our schools and hospitals open. </li></ul><ul><li>But in fact there may be more than two choices. Eg </li></ul><ul><li>If taxes are raised we can have both options. </li></ul>Keep schools and hospitals open Increase military expenditure