The Art of Reasoning Well
Reasoning Well Involves ArgumentsArgument does not mean a verbal dispute
An Argument Is A Series Of Statements, Called Premises, Leading To A Conclusion
Logic: The study of the formal principles of reasoning
Deductive Argument: the truth of the premises guarantees the truth of the conclusion
Inductive Argument: the truth of the premises makes the truth of the conclusion more probable
Deductive ArgumentsExample (Valid):1. If it snows, then it is cold (premise) 2. It snows (premise) 3. Therefore, it is cold (conclusion)
VALID DEDUCTIVE ARGUMENT: The argument is in the proper form
Deductive ArgumentsExample (Invalid):1. If it snows, then it is cold (premise) 2. It is cold (premise) 3. Therefore, it snows (conclusion)
Deductive ArgumentsINVALID : The argument is not in the proper form.
Informal testing for deductive validity: Can You Think of a counter example?If yes, the argument is invalid.
Deductive ArgumentsIf Tom Cruise is a bulldog then he has four legs (Premise) Tom Cruise is a bulldog (Premise) Therefore, Tom Cruise has four legs (Conclusion)
Is the Argument Valid?
Have we proven that Tom Cruise has four legs?
Deductive ArgumentsIf it is determined that the argument is valid it must next be determined if the argument is sound.
A sound argument is valid argument with true premises.
Deductive ArgumentsIf Tom Cruise is a bulldog then he has four legsTom Cruise is a bulldogTherefore Tom Cruise has four legsIs the Argument Sound?
1.All observed emeralds have been found to be green 2.Therefore, the next observed emerald will be green.
1.In the past, sugar cubes have dissolved in water 2.Thus, this sugar cube will dissolve in water.
1. 70% of BCCC students in the sample are from Bristol 2. Hence, 70% of BCCC students are from Bristol
Unstated PremisesMany times arguments have one or more unstated premises that need to be added to support the conclusion. Sallys dog is a bloodhound therefore it has a keen sense of smell
Unstated PremisesIt is February, so I will dress warmlyDrugs should not be legalized
Analyzing ArgumentsReconstruct the Argument
1. Find the conclusion.
2. Find the premises
3. Find any unstated premises
The glove doesnt fit so you must acquitConclusion: Defendant should be acquittedPremise(s): The glove doesn't fit the defendant (premise - stated) Unstated premises: If evidence does not fit the defendant, then the defendant should be acquitted (premise - unstated) The glove is evidence (premise - unstated)
Analyzing ArgumentsEvaluate the argument
1. Is the argument valid? (Can I think of a counter example?)
2. Are the premises true?
Evaluating the Argument1. Is the argument valid? (Can I think of a counter example?)
2. Are the premises true?
If evidence does not fit the defendant, then the defendant should be acquittedThe glove is evidence The glove doesn't fit the defendant Therefore, defendant should be acquitted
Logical FallaciesMistakes in logic when presenting our arguments.
Formal Fallacy: An invalid argument
Informal Fallacy: Type of bad reasoning that can only be detected by examining the content of the argument.
Informal FallaciesBegging the Question Assuming what you are trying to prove
Capital punishment is wrong because it is immoral
Informal FallaciesAd Hominem Attack Attack on your opponent rather that his or her argument The only reason that you think Capital punishment is wrong is because you are a bleeding heart liberal
Informal FallaciesRed Herring: Sidetracking the argument with an irrelevant issue Honda makes the best cars --- No they dont their workers are treated poorly
Informal FallaciesHasty Generalization: Drawing general conclusions from a small sample A number of professional athletes have been convicted of crimes therefore all professional athletes are criminals
ArgumentsGeorge bush is a good presidentGeorge Bush is a bad president