logic and critical thinking by karey perkins. rhetorical appeals: using logos, ethos, pathos logos =...

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  • Slide 1
  • LOGIC AND CRITICAL THINKING by Karey Perkins
  • Slide 2
  • RHETORICAL APPEALS: USING LOGOS, ETHOS, PATHOS LOGOS = LOGIC and REASON= Soundness of facts, evidence, statistics, and reasoning; soundness of authoritys statements outside self; well-documented evidence ETHOS = Credibility and reliability of writer him/herself; character and reputation of the author PATHOS = EMOTION = Appeal to needs, values, and attitudes; uses the emotional power of language
  • Slide 3
  • LOGOS: Reason, Facts ACME's new dihydro-cesium detonation process By combining cesium and dihydro-oxide in laboratory conditions, and capturing the released energy, ACME has promised to lead the way into the future. Our energy source is clean, safe, and powerful, according to laboratory tests. In 20 tests conducted over a period of 5 years, no pollutants were released into the atmosphere. The world will soon have an excellent source of clean energy. ACME is currently working toward a patent on our process. Our scientists are exploring ways to use the process in cars, houses, airplanes, and almost anything else that needs power. ACME batteries will be refitted with small dihydro-cesium reactors. Once the entire world is powered by ACMEs generators, we can all relax and enjoy a much easier life.
  • Slide 4
  • ETHOS: Credibility of Source Acme Gizmotronics, the company that you've trusted for over 100 years, has recently entered the World Wide Web! Now you can purchase our fine products through the Internet. Our quality gizmos, widgets, and thingamabobs can be shipped to you within minutes. All come with the famous lifetime guarantee that makes Acme the company that the world depends on for its gizmo needs.
  • Slide 5
  • PATHOS: Emotional Appeals CESIUM-BASED REACTOR KILLS! A baby turtle breaks free from the leathery shell of its egg, catching its first glimpse of its first sunrise. It pauses a moment to rest, unaware of the danger that lies so close to it. As the tide comes in, approaching the nest, it also approaches a small pile of metal: cesium. The water draws closer and closer, the turtle unsuspecting of the danger. Finally, the water touches the cesium. The nest is torn to bits in the resulting explosion, destroying even more of an endangered species. Why does this happen? One name: Acme. (Examples from: The Art of Rhetoric: Learning How to Use the Three Main Rhetorical Styles. Available at: (http://www.rpi.edu/dept/llc/webclass/web/project1/group4/ ))http://www.rpi.edu/dept/llc/webclass/web/project1/group4/
  • Slide 6
  • Inductive and Deductive Reasoning Inductive Reasoning: Reasons from specific to general Notices many facts and comes to a general conclusion No certainty possible Deductive Reasoning: Reasons from general to specific Starts with a hypothesis and inserts a fact and comes to a conclusion based on hypothesis Certainty can be possible if valid and true syllogism (say some people)
  • Slide 7
  • INDUCTIVE REASONING Reasoning from sensory observation of specific facts/evidence to general conclusion With inductive reasoning, there can NEVER be certainty, because only ONE example can modify or refute the conclusion. (This example can come from any future event, or events in remote places and times we are not able to observe.) Based on an accumulation of many facts (one fact = x): Observation of: x x x x x x x x x x x x Equals General Statement about Xs in future
  • Slide 8
  • Examples of inductive reasoning If I jump off the building, I will fall to the ground. (More specifically: Every time something with weight and mass is released from any height, it falls to the ground. Therefore, all things fall to the ground (law of gravity). Based on an evaluation and observation of multiple studies of adolescents who value peers more than parents, Judith Rich Harris concludes that peers matter more than parents in this age group. Whenever it snows or rains, it will eventually stop snowing or raining. So far all U.S. presidents have been male. Therefore, the next U.S. president will be male.
  • Slide 9
  • Faulty Inductive Reasoning Today I saw an 80 year old lady driving 40 miles an hour on 285, a 95 year old man going 50 mph on 400, and a 70 year old guy going 20 mph on Haynes Bridge Road. Conclusion: Old people drive slow. (This is a stereotype, or logical fallacy of inductive origin.) Jesse Helms said in the Mexican Foreign Affairs Subcommittee (to prevent immigration from Mexico): All Latins are volatile. (This is a stereotype, or logical fallacy of inductive origin.)
  • Slide 10
  • Deductive Reasoning Reasoning from general tenets and premises to specific conclusions. With deductive reasoning, there CAN be certainty. Syllogisms follow this format: Major Premise (general truth about life/humans) Minor Premise (specific fact that falls under the truth) Conclusion (a conclusion that can be drawn about the specific fact based on the first generalization)
  • Slide 11
  • Syllogism Examples Correct Syllogism: Major Premise: All mammals are warm-blooded animals. Minor Premise: No lizards are warm-blooded animals. Conclusion: Therefore, no lizards are mammals. Correct Syllogism: Major Premise: All humans are mortal. Minor Premise: All Greeks are human. Conclusion: Therefore, all Greeks are mortal. Descartes Syllogism (correct) Major Premise: Existence has be true if one is thinking. Minor Premise: I am thinking. Conclusion: I think, therefore, I am.
  • Slide 12
  • Syllogisms can be Valid or Invalid (reasoning in incorrect order) AND True or False (reasoning from a faulty major premise)
  • Slide 13
  • Examples of Faulty Syllogisms FALSE Syllogism (not TRUE -- false major premise) Major Premise: Blondes have more fun Minor Premise: Mary is blonde; Jane is brunette Conclusion: Mary has more fun than Jane. INVALID Syllogism (not VALID order of reasoning is incorrect): Major Premise: All dogs eat meat Minor Premise: Bob (a human) eats meat Conclusion: Bob is a dog.
  • Slide 14
  • Corrections Syllogism One: The first faulty syllogism proceeds from a FALSE major premise and therefore can be thrown out entirely. Syllogism Two: Major Premise: All dogs eat meat Minor Premise: Rover is a dog. Conclusion: Therefore, Rover eats meat.
  • Slide 15
  • Valid or invalid? True or False? Example One: Major Premise: When it snows the streets get wet. Minor Premise: The streets are getting wet. Conclusion: Therefore, it is snowing. Example Two: Major Premise: If you buy a Ferrari, you will instantly be popular. Minor Premise: Ed just bought a Ferrari. Conclusion: Ed will achieve instant popularity. Example Three: Major Premise: When the battery is dead, the car will not start. Minor Premise: The car will not start. Conclusion: Therefore, the battery is dead.
  • Slide 16
  • Corrections: Valid and True Example One: Major Premise: When it snows, the streets get wet. Minor Premise: It is snowing. Conclusion: Therefore, the streets are getting one. Example Two: Example Two proceeds from the beginning from a FALSE major premise (Ferraris give instant popularity) and therefore can be thrown out entirely. Example Three: Major Premise: When the battery is dead, the car will not start. Minor Premise: The battery is dead. Conclusion: Therefore, the car will not start.
  • Slide 17
  • Some types of syllogisms Modus Ponens Modus Tollens Hypothetical Syllogism Disjunctive Syllogism
  • Slide 18
  • Modus Ponens 1.If A then B 2.A 3.Therefore, B Examples: If its spring, then the birds are chirping Its spring. The birds are chirping. If a world government doesnt evolve soon, then wars will continue to occur A world government isnt going to evolve soon. Wars will continue to occur
  • Slide 19
  • Modus Tollens 1.If A then B 2.Not B 3.Not A Example: 1.If its spring then the birds are chirping 2.The birds arent chirping 3.Therefore, it isnt spring.
  • Slide 20
  • Hypothetical Syllogism 1.If A then B 2.If B then C 3. If A then C Example: 1.If we successfully develop nuclear fusion power, then power will become plentiful and cheap. 2.If power becomes cheap and plentiful, then the economy will flourish. 3.If we successfully develop nuclear fusion power, then the economy will flourish.
  • Slide 21
  • Disjunctive Syllogism 1.A or B 2.Not A 3.B Example: 1.Either Romney won in 2012 or Obama did. 2.Romney didnt win. 3.Obama did win.
  • Slide 22
  • LOGICAL FALLACIES TO AVOID Circular Reasoning/Begging the Question: Promising support for your claim but providing none Bandwagon/: Inviting readers to accept a claim because everyone else does or because the prestigious group does Argument from authority: Inviting readers to accept a claim because because the claim is put forth by someone in a position of authority though the authority is invalid. Slippery Slope: forecasting a series of events (usually disastrous) that will befall one if the first stated step is taken. Straw Man: Inserting a false or unrelated premise into an argument, and then proving the false or unrelated premise wrong as a claim that the initial argument is wrong. Appeal to Fear: scaring the reader to your point of view Appeal to Pity: substituting emotions for reasoning. Appeal to Force: abandoning reason and using or threatening strong arm methods by means of the political or physical power of the enforcer; might makes right Red Herring: introducing an irrelevant issue intended to distra

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