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Argument, Logic, & Logical Fallacies. What is an Argument? Based on 2 statements with a 3 rd that follows the first two. One major premise One minor premise.

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Presentation on theme: "Argument, Logic, & Logical Fallacies. What is an Argument? Based on 2 statements with a 3 rd that follows the first two. One major premise One minor premise."— Presentation transcript:

1 Argument, Logic, & Logical Fallacies

2 What is an Argument? Based on 2 statements with a 3 rd that follows the first two. One major premise One minor premise Conclusion Premise: statement used as evidence for a conclusion Conclusion: statement that is supported by at least one premise Arguments can be good or bad.

3 Bad Argument 1)Fido is my dog.major premise 2)Fido is a mother.minor premise 3)Therefore, Fido is my mother. conclusion HUH?????? Both premise 1 & 2 are true, so why is the conclusion ridiculous?

4 Good Argument 1)If Gandhi was a sadist, then he would have hurt people. 2)It is not the case that Gandhi hurt people. 3)Therefore, it is not the case that Gandhi was a sadist. THAT’S BETTER! Premises 1 & 2 are true, so the conclusion is true. Why does this one work?

5 Informal Fallacies (Logical Fallacies) The difference between the two earlier arguments is that one includes an informal fallacy. Aristotle cataloged many illogical patterns of reasoning, informal fallacies, in his book Fallacies of the Sophists. These help us detect bad argumentation. Sometimes there are exceptions, so these are only rough guidelines rather than absolute rules.

6 Argument against the Person (ad hominem) An attack on a person’s character instead of the content of the person’s argument. “Heidegger was a poor philosopher since he was a member of the Nazi party.” “Bob is an alcoholic, so don’t take his advice too seriously. “Jones would argue for gun control; he’s a democrat!”

7 Argument from Ignorance This is concluding that something is true just because you can’t prove it is false. “God must exist, since no one can show that he does not.” “How do you know you’re not a witch if you do not know what a witch is?” McCarthy: “I do not have much information on this except the general statement of the agency that there is nothing in the files to disprove his Communist connection.”

8 Appeal to Pity This is appealing to a person’s unfortunate circumstances in order to get someone to accept a conclusion. “You need to give me an ‘A’ in this course, or I will lose my scholarship if you don’t.” “I beg you to find Mrs. Bobbit not guilty of mutilating her husband because her home life was so traumatic!” “Yes, I murdered my parents, but take pity on me because now I’m an orphan.”

9 Appeal to the Masses (bandwagon effect) This means going along with the crowd in support of a conclusion. “All the other guys carry guns to school.” “Aw mom, everybody else’s mom is letting them go.”

10 Appeal to Authority This is when a person appeals to a popular figure who is not an authority in that area. “Einstein believed in God, so God must exist.” “Bill Gates dropped out of college and became a billionaire, so I can too.” “Bart Simpson likes Butterfingers, so they must be good.”

11 Irrelevant Conclusion (non sequitur) This is when a person draws a conclusion that does not follow from the evidence. “My business failed last year, so Obama is bad president.” “My shoe string broke; I guess that means I have to buy a new car.”

12 Slippery Slope A slippery slope argument is not always a fallacy. This is an argument that says adopting one policy or taking one action will lead to a series of other policies or actions also being taken without showing a causal connection. This is a form of non sequitur. “If we legalize marijuana, the next thing you know we'll legalize heroin, LSD, and crack cocaine.”

13 False Cause This is when a person infers a casual connection based on mere correlation. Or more simply, the argument assumes one event caused another just because one happened before the other. “The number of stroke victims in hospitals is directly proportional to the number of tar bubbles on the road; thus, tar bubbles cause strokes.” “Successful people wear expensive clothing; therefore, the best way to become a success is to have expensive clothes.”

14 Circular Reasoning (begging the question) This is implicitly using your conclusion as a premise. “God must exist since the Bible says that God exists, and the Bible is true because God wrote it.” “It is impossible to talk without using words, since words are necessary for talking.”

15 Equivocation This is an argument based on two definitions of one word. “Good steaks are rare these days, so you shouldn’t order yours well done.” Jones is a poor man, and he loses whenever he plays poker; therefore, Jones is a poor loser.” “You don’t find cars like yours in these parts, so don’t let your car out of your sight.”

16 Composition This is when a person assumes that the whole must have the properties of its parts. “Each part of this machine is light; therefore, the whole machine is light.” “A bus uses more gas than a car; therefore, all busses combined use more gas than all cars combined.”

17 Division This is the opposite of Composition—assuming that the parts of a whole must have the properties of the whole. “This corporation is important, hence each worker in this corporation is important.” “Students study Math & English; therefore, each student studies Math & English.”

18 Red Herring This argument introduces an irrelevant or secondary subject, thereby diverting attention from the main subject. Basically, its something that takes attention away from the real issue or point. “Side impact airbags in cars do not really increase safety, and, besides, most cars with side impact airbags are Japanese imports.” “The curfew law is the city council’s attempt to usurp parental authority.”

19 Straw Man This is an argument that distorts an opposing view so that it is easy to refute. Imagine a fight in which one of the combatants sets up a man of straw, attacks it, then proclaims victory. All the while, the real opponent stands by untouched. “Vote against gun control, since gun control advocates believe that no one should own any type of fire arm.” “If we liberalize the laws on beer, then any society with unrestricted access to intoxicants loses its work ethic and goes only for immediate gratification.” “Our society should be taxed less because it’s unjust for a society to neglect the poor.”

20 Sweeping Generalization (stereotyping) This is the fallacy of making a sweeping statement and expecting it to be true of every specific case. "Women are on average not as strong as men and less able to carry a gun. Therefore women can't pull their weight in a military unit."

21 PROPOSITIONAL LOGIC Sentential Logic

22 Assists in constructing arguments which fit valid argument forms. 1)If Gandhi was a sadist, then he would have hurt people. 2)It is not the case that Gandhi hurt people. 3)Therefore, it is not the case that Gandhi was a sadist. The logical structure of this argument is this: 1)if P then Q 2)not Q 3)therefore, not P Logic is founded on the concept of a proposition.

23 Propositions You must distinguish between three related concepts: Utterance: The most general form of verbal expression. Utterances include nonsense expressions, such as “ob la di ob la da,” as well as statements. Statement: an utterance which conveys meaning. Statements include questions, commands, expressions of feelings, and propositions. Proposition: An either true or false statement about the world. Every statement in an argument must be a proposition.

24 Complex Propositions  Simple propositions are only one type of proposition used in logic.  Complex propositions are a combination of two or more simple ones.  In constructing complex propositions, logicians use:  Four basic logical connectives: P and Q conjunction P or Q disjunction not P negation if P then Q conditional

25 FOUR LOGICAL CONNECTIVES Conjunction, Disjunction, Negation, Conditional

26 Conjunction  “P and Q”  “Bob is rich and Sam is poor.”  Simple proposition: P—Bob is rich  Simple proposition: Q—Sam is poor  Conjunction constructs can be disguised P, but Q P, although Q P; Q P, besides Q P, however Q P, whereas Q  “Sherman and Xavier are computer software pirates”  Translates to: “Sherman is a computer software pirate, and Xavier is a computer software pirate.”

27 Disjunction “P or Q” “Mom pawned her wedding ring or Mom sold her blood.” Simple proposition: P—Mom pawned her wedding ring. Simple proposition: Q—Mom sold her blood. The “P” and “Q” elements are referred to as disjuncts. Disjuncts can be switched around like conjunctions. Or can be used two ways: Inclusively: Mom could have pawned her ring, or she could have sold her blood, or both. Exclusively: “Mary is dead, or Mary is alive.” Mary can’t be both dead and alive at the same time. In logic, “or” is used only inclusively.

28 Negation “Not P” “It is not the case that Fido just left his territorial mark.” Simple proposition: P—Fido just left his territorial mark. A sentence with a negative word in it, not, never, or none, may often (not always) be translated into a negative proposition. Consider—“I knew that Jurgan was not really a Nazi.” This is an assertion about my knowledge; it does not translate into a negation.

29 Conditional “If P then Q” “If you eat of the forbidden fruit, then you will surely die.” Simple proposition: P—you eat of the forbidden fruit. antecedent Simple proposition: Q—you will surely die. consequent In conditionals, if the P’s and Q’s are switched around, it changes the meaning of the sentence. Consider—“If you die, then you will have eaten of the forbidden fruit.” These sentences clearly do not mean the same thing. Assume that everyone who eats the forbidden fruit subsequently dies; but not all who die will have eaten of the forbidden fruit.

30 Disguised Conditionals If P, it follows that Q P implies Q P entails Q P only if Q Whenever P, Q P, therefore Q P is a sufficient condition for Q Q follows from P Q is a necessary condition for P Q, since P

31 Nested Logical Connectives Complex propositions often contain several logical connectives “nested” within each other. “I will not hurt you and your old lady if you simply hand over your wallet.” Negation Conjunction Conditional If P then not (Q and R) P = you will simply hand over your wallet Q = I will hurt you R = I will hurt your old lady The benefit is that it is possible to put even very complicated propositions into standard form.

32 Valid Argument Forms Modus Ponens premise 1: if P then Q premise 2: P concl. 3: therefore, Q 1.If the president pushes the button, then a nuclear bomb will go off. 2.He pushed the button. 3.Therefore, a nuclear bomb will go off. Fallacious Modus Ponens: fallacy of affirming the consequent premise 1: if P then Q premise 2: Q concl. 3: therefore, P 1.If the president pushes the button, then a nuclear bomb will go off. 2.A nuclear bomb went off. 3.Therefore, the president pushed the button.

33 Valid Argument Forms Modus Tollens premise 1: if P then Q premise 2: not Q concl. 3: therefore, not P 1.If Bob desecrated the Bible, then he would have been struck by lightening. 2.It is not the case that he was struck by lightning. 3.Therefore, it is not the case that Bob desecrated the Bible. Fallacious Modus Tollens: fallacy of denying the antecedent premise 1: if P then Q premise 2: not P concl. 3: therefore, not Q 1.If Bob desecrated the Bible, then he would have been struck by lightening. 2.It is not the case that Bob desecrated the Bible. 3.Therefore, it is not the case that he was struck by lightning.

34 Valid Argument Forms Disjunctive Syllogism: (two versions) premise 1: P or Qpremise 1: P or Q premise 2: not Ppremise 2: not Q concl. 3: therefore, Qconcl. 3: therefore, P 1.Either Smith bites the dust, or Smith bites Jones. 2.It is not the case that Smith bites the dust. 3.Therefore, Smith bites Jones. Fallacious Disjunctive Syllogism: fallacy of asserting an alternative premise 1: P or Qpremise 1: P or Q premise 2: Ppremise 2: Q concl. 3: therefore, not Qconcl. 3. therefore, not P 1.Either Smith bites the dust, or Smith bites Jones. 2.Smith bites the dust. 3.Therefore, it is not the case that Smith bites Jones.

35 Valid Argument Forms Hypothetical Syllogism premise 1: if P then Q premise 2: if Q then R concl. 3: therefore, if P then R 1.If you bribe the officer, then he will tear up the ticket. 2.If he tears up the ticket, then you won’t pay a fine. 3.Therefore, if you bribe the officer, then you won’t pay a fine.

36 Sound & Unsound Argument The first step in forming a good argument is that it must be valid. However, a good argument must be valid and have all true premises. This is called soundness. Valid form but not true premises— 1.Either Uncle Bob is a tennis shoe, or Uncle Bob is a golfing shoe. 2.It is not the case that Uncle Bob is a golfing shoe. 3.Therefore, Uncle Bob is a tennis shoe. True premises but no valid form— 1.If the President was the pilot of Air Force One, then he could fly in the presidential plane. 2.The President can fly in the presidential plane. 3.Therefore, the President is the pilot of Air Force One. Two ways that an argument can be unsound: It will be invalid It will have at least one false premise.

37 Works Cited & Consulted Fieser, James. "ELEMENTARY LOGIC." The University of Tennessee at Martin - 9 Sept Web. 17 Oct "Logical Fallacies and the Art of Debate." California State University, Northridge. 29 Jan Web. 17 Oct


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