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 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? Mmmmmm m…Vodka!

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

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

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

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 A B C These Cs are not As 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 B C

14. Another example! Therefore some Bs are Cs A B C 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