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Reason Continued


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

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

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  • 1. Reason Continued…
  • 2. Recap types of logic:
    • Deductive Logic
    • Reasoning from the general to particular
    • Example:
      • all metals expand when heated.
      • A is a metal
      • Therefore A expands when heated
    • Its more certain but less informative than induction
    • Inductive logic
    • Reasoning from the particular to the general
    • Example:
      • Metal A expands when heated
      • Metal B expands when heated
      • Metal C expands when heated
      • Therefore all metals expand when heated
    • Its more informative, but less certain than deduction
  • 3. The relationship between reasoning and certainty
    • What percentage of the metal existing on our planet would you guess scientists have tested to see if it expands when heated?
    • What does this tell you about the certainty or otherwise of scientific laws?
  • 4.  
  • 5. What distinguishes good and bad generalisations?
    • Number – you should look at a reasonable amount of instances
    • Variety - You should look at a variety of instances
    • Exceptions – You should actively look for counter examples. This will help to guard against a confirmation bias.
    • Coherence – you should demand more evidence to support surprising claims than to support unsurprising ones.
    • 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.
    • Subject Area – generalisations are more reliable in some subjects than in others
  • 6. Logic as a pathway to truth
    • We have seen that reason provides a way of laying out information, in a way that sometimes helps us get closer to truth.
    • When using deductive reasoning one must be able to answer ‘yes’ to both of the following questions:
    • Are the premises true?
    • Is the argument valid?
  • 7. Logic as a pathway to truth
    • Premise 1) some Monks are Tibetans
    • Premise 2) All Tibetans are good at yoga
    • Therefore,
    • Conclusion: some monks are good at Yoga
    • Are the premises true?
    • Is the argument valid?
    • ..some evidence of Tibetans who are good at Yoga
    • So Premise 2) is possibly true
  • 8. Preserving truth
    • So, although we can’t be 100% certain of the truth of the 2 nd premise, unless we find evidence from every Tibetan,
    • And unless we have reason to believe that Tibetan monks generally shun yoga,
    • Although the argument is not strictly valid,
    • We can tentatively accept the truth of the conclusion.
    • This is because the scope of the claim could be fairly small .
    • We don’t need to find many Tibetan Monks who are good at Yoga for the conclusion to be true .
  • 9. Filling in the premises to an argument
    • When people argue in everyday life, they rarely set their arguments out in a formal way.
    • 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.
    • Therefore, you will sometimes have to fill in the premises to someone else’s argument, if you want it to make logical sense .
  • 10. Fill in the missing premise:
    • 1) Lucy goes to Oxford University
    • 2) Oxford only takes very intelligent students
    • Therefore: Lucy must be very intelligent.
    • 1) Graham is a politician
    • 2) All politicians are probably lying.
    • Therefore: Graham is probably lying
  • 11. Fill in the missing premise:
    • 1) Cheerleaders compete, train, and have a high level of physical fitness.
    • 2) All Olympic events involve competing, training and having a high level of physical fitness.
    • Therefore: Cheerleading should be an Olympic event
    • 1)it is natural to eat meat
    • 2) There is never anything morally wrong with anything natural
    • Therefore: There is nothing morally wrong with eating meat.
  • 12. Using Venn diagrams
  • 13. Venn diagrams help you work out if a syllogism or argument is valid
    • It is sometimes difficult to work out if a syllogism is true or false.
    • One way of working out what is going on is to draw a Venn diagram. Consider the following syllogism:
      • 1) all As are Bs.
      • 2) some As are Cs.
      • Therefore: some Bs are Cs.
    • 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 ...
  • 14. Using Venn diagrams
    • ...and to represent ‘ some As are Cs’ have the circle of Cs intersect the circle of As.
    • So it follows that ‘ somes Bs are Cs’
    • the argument is valid.
    B A C
  • 15. Task:
    • Can you use the following venn diagram to make a syllogism?
  • 16.  
  • 17.  
  • 18. Fallacies Types of invalid reasoning
  • 19. Types of Fallacy
    • The types of Fallacy we’ll focus on:
    • Post hoc ergo propter hoc
    • Ad Hominem Fallacy
    • Circular reasoning
    • Equivocation
    • False Dilemma
  • 20. Fallacies
    • Post hoc ergo propter hoc
    • Meaning: ‘ after this, therefore on account of this’
    • consists of assuming that because one thing, B , follows from another thing, A , then A must be the cause of B . eg:
      • 1) at 6pm the girls ate tomato soup
      • 2) at 7pm the girls committed murders
      • Therefore: tomato soup causes girls to murder
  • 21. Fallacies
    • Ad Hominem
    • Meaning: ‘ against the man’
    • consists of attacking or supporting a person rather than the argument itself . eg:
      • Raffles told me to vote conservative at the next election
      • Raffles would say that because he is a conservative counsellor
    • Although the ad hominem fallacy is committed mostly by criticising someone, it can also be committed by supporting them.
    • If I said ‘Martin Luther King jr was a Christian, so Christianity must be true ’
    • Then I am again focusing on the speaker rather than the argument.
  • 22. fallacies
    • Circular reasoning
    • Aka ‘ begging the question ’
    • Consists in assuming the truth of the thing you are supposed to be proving . Eg:
      • “ I know that Jesus was the Son of God because he said he was, and the Son of God would not lie.”
    • this is not an argument, but a reassertion of original position, with no appeal to reasons.
    • Anthony Flew’s example:
    • ‘ Three thieves are arguing about how to divide up 7 pearls they have stolen.
    • One picks up the pearls and gives two to each of the other two, keeping three for himself.
    • “ I get more because I’m the leader”
    • “ how come your the leader?”
    • “ because I’ve got more pearls.”
  • 23.  
  • 24. fallacies
    • Equivocation
    • This occurs when a word is used in two different senses in an argument.
      • 1) a hamburger is better than nothing
      • 2) Nothing is better than good heath
      • Therefore: a hamburger is better than good health.
    • This appears formally valid, because the premises follow from the conclusion.
    • But there is something wrong with it.
    • The problem lies with the word ‘nothing’ because it has a different meaning in each of the premises .
    • In the 1 st premise it means ‘not having anything ’
    • In the 2 nd it means ‘there is not anything’
    • Maybe this is why many argument s end up being about the meanings of words.
  • 25.  
  • 26. Fallacies
    • False Dilemma
    • This is the fallacy of assuming that there are only two alternatives , when there are in fact a wider range of options. Eg:
    • ‘ Do those who advocate an increase in military expenditure want to see schools and hospitals close?’
    • They imply that we only have two choices:
    • Either we increase military expenditure
    • Or we keep our schools and hospitals open.
    • But in fact there may be more than two choices. Eg
    • If taxes are raised we can have both options.
    Keep schools and hospitals open Increase military expenditure