REQUIRED DELIVERABLES Topic & IB Advisor: May 3rd Research question: May 10 Bibliography: May 17 First draft of outline: EXAM

ONCE YOU HAVE YOUR SUPERVISOR AND TOPIC YOU DO NOT REST ON YOUR LAURELS, PAT YOURSELF ON THE BACK, OR TAKE A BREAK UNTIL THE NEXT DEADLINE LOOMS. THERE ARE NO MORE BREAKS. START RESEARCHING READ, READ, READ DO NOT JUST SIT AND PONDER, WONDER, AND/OR SPECULATE. SPECULATION IS NOT NECESSARY, YOU ARE ABLE TO FIND THE ANSWERS YOU MUST READ!

What is it? How does it work? Why does it matter? You do not reason a man out of something that he was not reasoned into All generalizations are false, including this one Deductive logic What is it? How does it work? Why does it matter? Critical reason is the only alternative to violence so far discovered. Logic is the beginning of wisdom, not the end

An example.. Sherlock Holmes (the master of deductive logic) speaking to a police officer about the theft of an expensive racehorse… Police Officer: “Holmes, does any one aspect of the crime strike you as significant?” Holmes: “Yes, the curious incident of the dog in the night time” Police Officer: “But the dog did nothing in the night time!” Holmes: “That was the curious incident!” What was Holmes’ reasoning?

The deductive reasoning.. Watchdogs bark at strangers The Watchdog did not bark at the thief Therefore the thief was not a stranger

More examples.. It must be on your desk You know that you left your phone either in your pocket or on your desk Your phone isn’t in your pocket Therefore... It must be on your desk

More examples.. You know that Lake Michigan is a fresh water lake You know that sharks cannot live in fresh water Therefore... There cannot be any sharks in Lake Michigan

The benefits? You don’t have to check Lake Michigan to know that there aren’t any sharks in it: deductive logic tells you that there are no sharks in the West Lake. If...

So what is deductive reasoning? Any form of reasoning that moves from the general to the particular e.g. “All dogs are happy (general) Fido is a dog (particular) Therefore Fido….

Syllogisms The kind of deductive argument that we just looked at is known as a syllogism A syllogism consists of: Two premises and a conclusion. One premise is Major (a generalization: “All...” or “No...”); the other Minor (a particular example) Three terms, each of which occurs twice (dogs, happy, Fido) Quantifiers such as ‘all, some or no’

Truth Vs Valid – What is the difference?

Truth Vs Valid – which is this? All rocket scientists are stupid Bill Gates is a rocket scientist Therefore Bill Gates is stupid

Truth Vs Valid – which is this? All panthers are pink. George Washington is a panther. George Washington is pink.

It is Valid! Both the PREMISES are false The CONCLUSION is false Yet the ARGUMENT ITSELF IS VALID! The validity of an argument has nothing to do with the truth or falsity of its premise. So just because an argument is valid, it does not follow that the conclusion is true. To be sure that the conclusion of an argument is true, you must be able to answer “yes” to both of the following questions: Are the premises true? Is the argument valid?

WHAT ABOUT THIS ONE? All tacos are teachers Mrs. Craig-Salmon is a taco Therefore Mrs. Craig-Salmon is a teacher

Valid Both the premises are false But the conclusion is true However the argument is still VALID

This one?... All toasters require electricity This classroom has no toaster Therefore this this classroom has no electricity

INVALID The premises are both true The conclusion is false This is the one combination where the argument MUST be invalid

LOGIC - COMPLETE THE SYLLOGISM 1. MAJOR PREMISE: All carrots are orange MINOR PREMISE: Some vegetables are carrots CONCLUSION:

LOGIC - COMPLETE THE SYLLOGISM 2. MAJOR PREMISE: No students do their homework MINOR PREMISE: I am a student CONCLUSION:

LOGIC - COMPLETE THE SYLLOGISM 3. MAJOR PREMISE: All books are boring MINOR PREMISE: This is a book CONCLUSION:

LOGIC - COMPLETE THE SYLLOGISM 4. MAJOR PREMISE: Tall people eat vegetables MINOR PREMISE: I eat vegetables CONCLUSION:

LOGIC - COMPLETE THE SYLLOGISM 5. MAJOR PREMISE: Swimmers like cold water MINOR PREMISE: You are a swimmer CONCLUSION:

LOGIC - COMPLETE THE SYLLOGISM 6. MAJOR PREMISE: A bachelor is a man who is not married MINOR PREMISE: John is not a bachelor CONCLUSION:

LOGIC - COMPLETE THE SYLLOGISM 7. MAJOR PREMISE: Every country has a capital city MINOR PREMISE: Peru is a country CONCLUSION:

DIY – With your table make your own valid syllogisms Two true premises and a true conclusion One true premise, one false premise and a false conclusion Two false premises and a true conclusion Two false premises and a false conclusion One of each.

Pure logic Concerned merely with the structure of arguments, it doesn’t matter if the premises are false, or even meaningless! All that matters is does the conclusion follow logically from the premises. E.g. : All blims are blams Some blims are bloms Therefore some blams are bloms

Aghhhh – my head hurts! Algebra in TOK! All A’s are B’s Some A’s are C’s Therefore some B’s are C’s IS THIS VALID OR INVALID? UNDER WHAT CIRCUMSTANCES IS THIS TRUE?

What’s the point? Removes ‘belief bias’ Sometimes we tend to believe an argument is valid because we already agree with the conclusion E.g. Democrats are in favor of free speech Dictators are not Democrats Therefore all dictators are opposed to free speech This is NOT a valid argument

Using Venn diagrams Venn diagrams can be a useful way of picturing a Syllogism and determining whether an argument is valid All A’s are B’s Some A’s are C’s Therefore some B’s are C’s IS THIS VALID OR INVALID? UNDER WHAT CIRCUMSTANCES IS THIS TRUE?

Using Venn diagrams All A’s are B’s Venn diagrams can be a useful way of picturing a Syllogism and determining whether an argument is valid All A’s are B’s B A

Using Venn diagrams Some A’s are C’s C B A

Using Venn diagrams Therefore some B’s are C’s C B A

Using Venn diagrams C How would you change it to make it true? Venn diagrams can be a useful way of picturing a Syllogism and determining whether an argument is invalid All A’s are B’s All B’s are C’s All C’s are A’s C B A How would you change it to make it true? How would you change it to make it true?

Enthymeme’s Incomplete arguments that exclude a premise because it is considered obvious /assumed. The validity of an argument has nothing to do with the truth or falsity of its premise. So just because an argument is valid, it does not follow that the conclusion is true. To be sure that the conclusion of an argument is true, you must be able to answer “yes” to both of the following questions: Are the premises true? Is the argument valid?

Supply the missing premise for these enthymemes Jenny goes to Oxford University, so she must be very intelligent Drugs should be legalized because they only harm the addict Graham is a politician, so he is probably lying. Cheerleading should be an Olympic event because cheerleaders compete, train and have a high level of physical fitness Since it is natural to eat meat, there is nothing morally wrong with it

But where do our premises come from? INDUCTIVE REASONING…! To be continued…. (Duh, Duh, Duuuuhhhhhhh!) But one thought before you go. How can you be sure that someday you will die? What evidence do you have for your belief?

Bibliography Much of this presentation is shamelessly based upon material from the excellent TOK book by Richard van de Lagemaat – thanks go to him!

But where do our premises come from? INDUCTIVE REASONING…! To be continued…. (Duh, Duh, Duuuuhhhhhhh!) But one thought before you go. How can you be sure that someday you will die? What evidence do you have for your belief?