 Reason A Way of Knowing

 Logic is the beginning of wisdom, Valeris, not the end. - Spock

Introduction  Process of Sherlock Holmes  Watchdog barking  Assumptions are called premises  Rationalism declares reason is the most important source of knowledge  Rationalists love logic and math, suspicious of perception  Fallacies are invalid patterns of reasoning  Which is more reliable – reason or perception?

Deductive Reasoning  General to the particular  All dogs are mammals  Fido is a dog  Fido is a mammal  Syllogism – consists of two premises, a conclusion, three terms and quantifiers  First two were truths, third was validity  Argument can be valid while premises and conclusions are not

Exercise in Reasoning  Two true premises and a true conclusion  One true premise, one false premise 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

Deductive Reasoning Preserves Truth  Must be able to say  Premises are true  Argument is valid  If you begin with truth you will end with it  Enthymeme  Argument that is incomplete because premises are obvious

Exercise in Enthymemes  Fill in the missing premise.  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 fitness.  Since it is natural to eat meat, there is nothing morally wrong with it.

Discussion Questions  How sure are you that some day you will die? What evidence do you have?  What does it mean to die? What happens? What evidence do you have?

Inductive Reasoning  From the particular to the general  Every human I know has died  I have never heard of a human that did not die  All human beings die  Allows us to make generalizations about the world  Inherited wisdom  Example?  “You should never generalize” already a contradiction  How can seemingly obvious generalizations turn out to be wrong?  Examples  Confirmation bias

 Confirmation Bias Activity

Fallacies in Informal Reasoning  Post hoc ergo propter hoc  Assuming B is a result of A because it always follows A  In America, as churches increase, so do prostitutes  Ad hominem  Attacking the person not the argument  You are too young to understand  Circular reasoning  Assuming truth of something you are supposed to be proving  You can’t me a C because I don’t get Cs

Fallacies in Informal Reasoning  Special pleading  Use of double standards  Watering flowers because they are prize-quality if there is a drought  Equivocation  When a word is used in two different sense in an argument  Ad ignorantiam  Something is true on the grounds that there is no evidence to disprove it  False analogy  Assuming two things are similar in some respects, must be similar in all respects  False dilemma  Stating only two options exist when there are actually more  Loaded questions

 Exercise in Informal Reasoning

 Thinking Outside the Box Explain the following

What happened here?  A man walks into a bar and asks the barman for a glass of water. The barman pulls out a gun and points it at the man. The man says “Thank you” and walks out.  A man is lying dead in a field. Next to him there is an unopened package. There is no other creature in the field. How did he die?  Anthony and Cleopatra are lying dead on the floor in a villa in Egypt. Nearby is a broken bowl. There is no mark on either of their bodies and they were not poisoned. How did they die?  A man rode into town on Friday. He stayed three nights and then left on Friday. How come?

What happened here?  Two boxers are in a match. The fight is scheduled for 12 rounds but ends after 6 rounds, after one boxer knocks out the other boxer. Yet, no man throws a punch. How is this possible?  In your cellar there are three light switches in the OFF position. Each switch controls one of three light bulbs on the floor above. You may move any of the switches but you may only go upstairs to inspect the bulbs one time. How can you determine the switch for each bulb with one inspection?

What happened here?  A landscaper is given instructions to plant four special trees to that each one is exactly the same distance from the others. How would you arrange the trees?  Connect the nine marks using only four straight lines and without taking your pen off the paper.