2Outline 1 – Arguments: valid vs sound 2. Conditionals 3. Common Forms of Bad Arguments
3Outline 1 – Arguments: valid vs sound 2. Conditionals 3. Common Forms of Bad Arguments
4Arguments Argument: a sequence of sentences where one (the conclusion) is meant to follow from or be supported by the others (the premises). P1 All men are mortal. P2 Socrates is a man. C. Socrates is mortal. Premise 1 Premise 2 Conclusion Arguments can be: 1.Valid / Invalid 2.Sound / Unsound
5 Valid Arguments Valid Arg.: -The conclusion logically follows from the premises - An argument where it is impossible for the premises to be true and the conclusion false. P1 Jackie’s baby is a girl or a frog. P2 Jackie’s baby is not a frog. CC Jackie’s baby is a girl. P1 All men are mortal. P2 Socrates is a man. CC Socrates is mortal. VALIDITY = LOGICAL FORM
6 Valid Arguments Attention! -Just because an argument is valid, it does not mean that its conclusion is true - Just because an argument is invalid, it does not mean that its conclusion is false. P1 Jackie’s baby is a girl or a frog. P2 Jackie’s baby is not a frog. CC Jackie’s baby is a girl. P1 No reptiles has big ears P2 Bugs Bunny is not a reptile. CC Bugs Bunny has big ears. But if the premises are true and the argument is valid, then the conclusion is always true
8 Valid vs Sound Valid Arg which is not sound: P1 Jackie’s baby is a cabbage or a frog. P2 Jackie’s baby is not a frog. C. Jackie’s baby is a cabbage. Sound Arg: P1 Jackie’s baby is a girl or a boy. P2 Jackie’s baby is not a boy. C. Jackie’s baby is a girl.
9 Conclusion: Good and Bad Arguments Good arguments are SOUND, ie are valid and possess true premises – They support the conclusion Bad arguments are either: -Invalid : the logical form is incorrect, or -Unsound: the premises are false These are the two ways in which you can criticize an argument from a philosopher ! To Remember: distinction valid / sound arguments
10Outline 1 – Arguments: valid vs sound 2. Conditionals 3. Common Forms of Bad Arguments
11Conditionals Conditional : IF P THEN Q / P Q Necessary and Sufficient conditions: IF P THEN Q P Sufficient Q Necessary If you are pregnant then you put on weight
12Conditionals Attention: IF P THEN Q is NOT equivalent to IF Q then P Attention: IF P THEN Q is NOT equivalent to IF Q then P If you are pregnant, you put on weight Is NOT equivalent to: If you put on weight then you are pregnant
13Contrapositions Contraposition: IF P THEN Q is equivalent to IF not Q then not P Contraposition: IF P THEN Q is equivalent to IF not Q then not P If you are pregnant, you put on weight IS equivalent to: If you DON’T put on weight then you are NOT pregnant
14 Conclusion on Conditionals To Remember: 1.What a conditional is 2.The distinction between necessary and sufficient conditions 3.The notion of contraposition To Remember: 1.What a conditional is 2.The distinction between necessary and sufficient conditions 3.The notion of contraposition
15Outline 1 – Arguments: valid vs sound 2. Conditionals 3. Common Forms of Bad Arguments
16 Using a conditional the wrong way Two ways to use a conditional the wrong way: Affirming the antecedent / Denying the consequence Two ways to use a conditional the wrong way: Affirming the antecedent / Denying the consequence Affirming the antecedent P If you are pregnant, Hence Q then you gain weight Affirming the consequent Q If you gain weight, Hence P then you are pregnant Denying the antecedent Non Q If you are not pregnant, Non P then you don’t gain weight Denying the consequent Non P If you don’t gain weight, Non Q then you are not pregnant IF P THEN Q If you are pregnant, then you gain weight IF P THEN Q If you are pregnant, then you gain weight
17 Circular Arguments Circular arguments assume what they want to prove. The police did not beat the suspect because beating suspects in not something that police ever do. Darwin's account of evolution is just a theory. A theory is an unproven hypothesis. So, there is no compelling reason to believe Darwin's theory.
18 Consequential Fallacy Consequential fallacy: confuse the consequences of holding a belief with evidence for that belief. Darwin’s theory is false because if it were true, there would be no morality.
19Equivocation Equivocation: to use an ambiguous term in different ways in an argument. Mad men should not be allowed to make decisions about the lives of others. My father is mad. He should not make an important decisions about my life.
20 Appeal to Consensus Appeal to Consensus: one appeals to consensus to establish a claim. Most people believe that McDonals is the best restaurant in the world. McDonalds is the best restaurant in the world.
21 Slippery Slope Slippery slope: incorrectly reasons that the arbitrariness of marking a distinction along some continuum shows that no distinction is possible. There is no agreed upon number of hair that qualifies someone as bald. Therefore, there is no difference between being bald or hairy.
22 Misleading Vividness Misleading vividness: particularly vivid information is weighted more than other information in coming to a conclusion. “Is there a post-abortion syndrome?” New York Times, January 21, 2007 Note that the argument can be criticized without criticizing the people who make the claims, nor even disagreeing with them about the moral status of abortion.
23 Genetic Fallacy Genetic fallacy: taking the source of a claim as evidence for or against the claim. Tom Cruise said that there is no such thing as a chemical imbalance of the body. Tom Cruise is crazy. Therefore, there is such thing as a chemical imbalance of the body. Note that the argument can be criticized even if the conclusion is true.
24 Straw Man Straw man: misrepesenting someone’s position, arguing against it, and supposing that the actual position is defeated.
25 Straw Man Nigel: I believe that some kinds of sexual lifestyles are morally wrong. Basil: So, you’re saying it’s OK for rednecks to beat up gay people? Nigel: No, I’m not saying that at all. All people in our society should be protected from having unwanted violence inflicted upon them. I’m just saying I think their chosen lifestyles are immoral.
26 Straw Man Basil: What makes you think it’s OK for you to force your morality on everyone else? Nigel: I haven’t said anything about forcing my morality on anybody. All I did was give my opinion about a certain moral issue. I didn’t use any force or even the threat of force to coerce others to agree with me.
27 Straw Man Basil: But you are saying that you don’t think gay people should have the same rights as straight people, right? Nigel: No. I think all people in a democratic society should have the same rights. That means that people should have the right to pursue lifestyles that others think are immoral. I haven’t said anything about depriving people of their rights or inflicting violence upon them. I’m only giving my opinion about the morality of their behavior. Bebee (2003) ``Good and Bad Arguments.’’
28Feelings Feelings: a person argues for a position by indicating that they feel a certain way. Problem: No one cares how you feel. Solution: Use good arguments! More important problem: There is no warrant the think that your feelings about something are correlated to the truth or falsity of a proposition.
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