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

3. 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!

4. 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

5. 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?

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

7. 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

8. 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

9. 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...

10. 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….

11. 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’

12. Truth Vs Valid –
What is the difference?

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

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

15. 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?

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

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

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

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

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

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

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

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

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

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

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

27. 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.

29. 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

30. 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?

31. 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

32. 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?

33. 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

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

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

36. 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?

38. 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?

39. 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

40. 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?

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

42. 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?