Reason

1. Reason Theory of Knowledge

2. Think… • Sherlock Holmes • Spock

3. What does logic seem able to do? • Allow us to go beyond the evidence of our senses • Provide certainty

4. Deductive Reasoning • Moves from the general to the particular • Can be expressed in the form of a syllogism (2 premises + 1 conclusion containing 3 terms + various quantifiers) • Be careful not to confuse validity with truth: an argument may be valid, but its conclusion is only as true as the premises it contains • The ability to analyze arguments is useful as it can help us to avoid belief bias, the tendency to believe that an argument is valid simply because we happen to agree with its conclusion • Frequently used in math

5. Deductive Logic in Practice • Most useful when it is based on true premises • Gives us more certainty, but less information • Because the premises of an argument are always based on inductive reasoning (generalizations), there is always the possibility that they could be wrong • In everyday life, people often leave out one of the premises (called an enthymeme)

6. Inductive Reasoning • Moves from the particular to the general • In other words, it goes beyond first hand experience to make inferences about things that have not been directly experienced • Inherent in language as well as science • Gives us more information, but less certainty

7. Inductive Reasoning in Practice • Often make hasty generalizations (made worse by our tendency toward confirmation bias – tendency to remember only evidence that supports our beliefs) • Even well-established generalizations can be wrong

8. Good Generalizations • Large number of specific instances • Wide variety of specific instances • Look for counter-examples • Demand even more evidence for surprising claims • Keep the subject area in mind (e.g. a larger number of specific instances may be required in the human sciences) • No precise rules, though: the more evidence we have the more confident we can be in our generalizations

9. The 10 Deadly Fallacies • Hasty generalizations • Post hoc ergo propter hoc • Ad hominem • Circular reasoning • Special pleading • Equivocation • Argument ad ignorantiam • False analogy • False dilemma • Loaded question

10. What is bad reasoning caused by? • Ignorance • Laziness • Pride • Prejudice

11. Three Laws of Thought • The law of identity • The law of non-contradiction • The law of the excluded middle • Logic is the basis for all meaningful communication

12. But… • How can we be sure that these laws in fact describe reality as it truly is? • Categories are never clear-cut, they are only approximations • Reality is constantly in flux • Problem of induction

13. Lateral Thinking • Thinking outside of the box • Escaping “the prison of consistency”

14. Reference • van de Lagemaat, R. (2011). Theory of Knowledge for the IB Diploma. Cambridge University Press: Cambridge, UK.