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! • 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?

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

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

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

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

Another example • All As are Bs A B

Another example • All Bs are Cs A B C

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

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

Another example! • All As are Bs A B

Another example! • Some As are Cs A C B

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

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

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

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

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

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

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

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

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

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