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Can you think of five famous people who you feel are rational/logical?

Can you think of five famous people who you feel are rational/logical?. Deciding whether a syllogism is valid. Trying to decide if a syllogism is valid is not easy. Venn diagrams can help (at last a good use for Venn diagrams!). Deciding whether a syllogism is valid. Mmmmmmm…Vodka!.

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Can you think of five famous people who you feel are rational/logical?

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  1. Can you think of five famous people who you feel are rational/logical?

  2. Deciding whether a syllogism is valid Trying to decide if a syllogism is valid is not easy. Venn diagrams can help (at last a good use for Venn diagrams!)

  3. Deciding whether a syllogism is valid Mmmmmmm…Vodka! • Some IB students are from Russia • All Russians are good at drinking vodka • Therefore some IB students are good at drinking vodka Is this a valid argument?

  4. Using Venn diagrams • Some IB students are from Russia IB Students who are Russian IB Students Russians

  5. Using Venn diagrams • All Russians are good at drinking vodka Good vodka drinkers IB Students Russians

  6. Using Venn diagrams • Therefore some IB students are good at drinking vodka Good vodka drinkers IB Students Russians

  7. Another example • All As are Bs • All Bs are Cs • Therefore all Cs are As

  8. Another example • All As are Bs A B

  9. Another example • All Bs are Cs A B C

  10. Another example • Therefore all Cs are As These Cs are not As A B C The syllogism is not valid

  11. Another example! • All As are Bs • Some As are Cs • Therefore some Bs are Cs

  12. Another example! • All As are Bs A B

  13. Another example! • Some As are Cs A C B

  14. Another example! • Therefore some Bs are Cs A C B The syllogism is valid

  15. Now your turn Using Venn diagrams in your notebooks, decide whether each of the following arguments is valid or invalid.

  16. Valid or invalid • All Norwegians eat hotdogs • Edward eats hotdogs • Therefore Edward is Norwegian

  17. Valid or invalid • No Swedes have red noses • Mr Luitjens has a red nose • Therefore Mr Luitjens is not a Swede

  18. Valid or invalid • All IB1 boys are brave • Some brave people are compassionate • Some IB1 boys are compassionate

  19. Valid or invalid • Some physicists are frauds • Some frauds are not wealthy • Therefore some physicists are not wealthy

  20. Valid or invalid • All Norwegians have dogs • No good football players have dogs • Therefore no Norwegians are good football players

  21. Valid or invalid • All clever girls are red-headed • All red heads are rich • Therefore all clever girls are rich

  22. Valid or invalid • No teachers are clever • No IB1 students are clever • Therefore no IB1 students are teachers

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