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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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### Transcript

• 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
• 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
• 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
• 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
• 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”
• “ 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