LOGIC AND

CRITICAL THINKINGby

Karey Perkins

RHETORICAL APPEALS: USING LOGOS, ETHOS, PATHOS

• LOGOS = LOGIC and REASON= Soundness of facts, evidence, statistics, and reasoning; soundness of authority’s 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

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 ACME’s generators, we can all relax and enjoy a much easier life.

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.

PATHOS: Emotional AppealsCESIUM-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/ ))

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)

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 x x x x x x x x x x x xEquals

General Statement about X’s in future

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.

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.)

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)

Syllogism ExamplesCorrect 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.

Syllogisms can be

• Valid or Invalid (reasoning in incorrect order)

AND• True or False (reasoning from a

faulty major premise)

Examples of Faulty SyllogismsFALSE 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.

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.

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.

Corrections: Valid and TrueExample 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.

Some types of syllogisms

• Modus Ponens• Modus Tollens• Hypothetical Syllogism• Disjunctive Syllogism

Modus Ponens1. If A then B2. A3. Therefore, B

Examples:• If it’s spring, then the birds are chirping• It’s spring.• The birds are chirping.

• If a world government doesn’t evolve soon, then wars will continue to occur• A world government isn’t going to evolve soon.• Wars will continue to occur

Modus Tollens

1. If A then B2. Not B3. Not A

Example:1. If it’s spring then the birds are chirping2. The birds aren’t chirping3. Therefore, it isn’t spring.

Hypothetical Syllogism

1. If A then B2. If B then C3. 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.

Disjunctive Syllogism

1. A or B2. Not A3. B

Example:1. Either Romney won in 2012 or Obama did.2. Romney didn’t win.3. Obama did win.

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 distract readers from the relevant issues – going off on a tangent.

• Self Contradiction: using two premises that can’t be simultaneously true

• Ad Hominem: (attacking the man) attacking the qualities of the people holding an opposing view rather than the substance of the view itself.

• Guilt by Association: kind of “ad hominem” attack implying that an individual’s arguments, ideas, or opinions lack merit because of that person’s activities, interests or associates

• False Cause or “Post Hoc” Fallacy: (from Latin: post hoc, ergo propter hoc, meaning “after this, therefore because of this”): assuming that because A preceded B, then A must have caused B.

• False Analogy: Assuming that because two things are alike in similar ways, they must be alike in other ways

• Either/Or Fallacy (False Dilemma): assuming that a complicated question has only two answers—one good, and one bad, both good, or both bad.

• Hasty Generalization: making a claim on the basis of inadequate evidence. Generalizing about something on the basis of too little evidence.

• Stereotyping is a type of Hasty Generalization applied to a group of people.

• Sweeping Generalization: making an insupportable statement, often using absolute statements such as all, always, never, and no one.

• Non Sequitur: (Latin: It does not follow): linking two or more ideas that in fact have no logical connection; the statement does not follow logically from what has just been said

• Card Stacking/Special Pleading: Ignores evidence on the other side of the question; only selecting those items that will build the best (or worst) possible case.

• Oversimplification/Reductive Fallacy: Oversimplifying (reducing) the relation between causes and effects

• Quibbling: Nitpicking at insignificant or possible errors in someone else’s basically valid and sensible argument

• Language Fallacies:• Emotional, biased, or slanted language• Equivocation• Ambiguity or obfuscation• Euphemism or PC• Doublespeak• Pretentious language• Bureaucratic language• Jargon

What is logically wrong with the following statements?

• The Bible is true because it says so.

• Boxing is dangerous because it is an unsafe sport.

Circular Reasoning/Begging the Question

• A. Therefore, A.• promising support/evidence/reasoning for your claim but

providing none

• Promising: Claim Support

• Delivering:

Claim (Support)

??

• Billy Joe is honest; therefore, he will get a good job

Non Sequitur

• (Latin for “It does not follow”): linking two or more ideas that in fact have no logical connection

• Missing is the unstated assumption that “honest people get good jobs” which is not always true.

??

• That candidate smoked pot when he was in college; therefore, he should not be president of the United States.

• That candidate had an affair; therefore, he should not be president of the United States.

Ad Hominem“Attacking the Man”

• attacking the personal qualities of the people holding an opposing view rather than the substance of the view itself

• In this case, the candidate may well be an excellent president and policy maker even though we may prefer not to have him as our husband.

??

• Jane is friends with Bob who was caught embezzling from the company; therefore, she should be fired.

Guilt by Association

• A kind of “ad hominem” attack implying that an individual’s arguments, ideas, or opinions lack merit because of that person’s activities, interests or associates

??

• Professor Perkins, if I don’t make an “A” in your class I won’t get my HOPE scholarship next semester.

• A plaintiff’s attorney brings his injured client, who is seeking compensatory damages, into the courtroom and plays up the injury in front of the jury (“A Civil Action”)

Appeal to Pity

• substituting emotions for reasoning; an appeal to emotion, in which the altruism and mercy of the audience are appealed to

??

• When Lyndon Johnson was running for president, his team ran a commercial of a little girl in a field holding a daisy, then an atomic bomb went off in the background. http://www.youtube.com/watch?v=ExjDzDsgbww

• The Bush campaign ran a 2004 commercial showing images from 9/11. (It was immediately withdrawn due to the families of victims complaining).

Appeal to Fear

• Tries to scare the reader to your point of view

??• Mom, I should be able to go to Underground Atlanta

to see the free Weezer concert that lasts til 1 AM – all my friends’ moms are letting them go.

• Despite the cost, impending gas crisis, and the harm to the environment, it is desirable to own an SUV because successful people do.

• More people in America drink Budweiser than any other beer; therefore, it must be the best beer and you should buy it.

Bandwagon

• Inviting readers to accept a claim because everyone else does or because a prestigious group does

??

• Television commercials that advertise their product using famous stars, for example, Ray Charles advertising Coke.

• Matt Damon should write an expose about the CIA since knows all about it; he was in the Bourne trilogy.

False Authority

• Citing the opinion of an expert who has no real claim to expertise on the topic

??

• You should go on the “Lose Weight Overnight” diet plan because Mary Smith and Tom Jones lost 100 pounds total in three months on it.

Card StackingSpecial Pleading

• Ignores evidence on the other side of the question

• Only selecting those items that will build the best (or worst) possible case.

??

• The new mayor took office last January and crime in the streets has already increased 25 percent.

• A new weather satellite was launched last week and it has been raining ever since.

• After that black cat crossed my path this morning, I got into a car accident. That cat was bad luck.

Post Hoc FallacyFalse Cause

• (from Latin: post hoc, ergo propter hoc, meaning “after this, therefore because of this”): assuming that because A preceded B, then A must have caused B.

??

• Banning pesticides to improve the environment is as impractical and unfeasible as banning the automobile.

• Education cannot prepare men and women for marriage. Trying to educate them for marriage is like trying to teach them to swim without allowing them to go into the water. It can’t be done.

False Analogy

• using a comparison in which two things are alike in one way to justify that they will be alike in another way. However, the similarities are irrelevant to the claim the analogy is intended to support. 1. A is like B.

2. B has property P. 3. Therefore, A has property P.

??• America: love it or leave it.

• We have only two choices: ban nuclear weapons or destroy the earth.

• Either we go to war against Iran, or the United States will suffer another terrorist attack.

Either/Or Fallacy and False Dilemma

• Stating that only two alternatives exist when in fact there are more than two

??• Teenagers are reckless drivers

• America is the best place to live (stated by one who has rarely visited other countries)

• “All Latins are volatile people” Jesse Helms to the Mexican Foreign Affairs

Subcommittee (to prevent immigration from Mexico)

Hasty Generalization

• Generalizing or making a claim on the basis of inadequate evidence.

??

• Why spend money on solving the problem of global warming when we ought to be doing something about the terrorists?

Red Herring

• introducing an irrelevant issue intended to distract readers from the relevant issues – going off on a tangent: 1. Topic A is under discussion. 2. Topic B is introduced under the guise of being

relevant to topic A (when topic B is actually not relevant to topic A).

3. Topic A is abandoned.

??

• If we make handguns illegal, the state will gain too much power and eventually put us all in concentration camps for the slightest infraction.

• If we legalize marijuana, eventually everyone will start smoking it regularly (at 4:20) and then they’ll want to go on to more kinds of drugs – soon heroin will become legal and most of America will become heroin addicts.

Slippery Slope

• forecasting a series of events (usually disastrous) that will befall one if the first stated step is taken

??

• Only when nuclear weapons have finally destroyed us will we be convinced of the need to control them.

Self Contradiction

• using two premises that can’t be simultaneously true

??

• After Will said that we should put more money into health and education, Warren responded by saying that he was surprised that Will hates our country so much that he wants to leave it defenseless by cutting military spending.

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:

1. Person A has position X.2. Person B presents position Y (which is a distorted or

completed unrelated version of X).3. Person B attacks position Y.4. Therefore X is false/incorrect/flawed.

??

• “I am firm, you are stubborn, he is pigheaded.” – Bertrand Russell

• “Friendly fire” – military term for killing your own team by mistake

• “Collateral damage” – military term for people who are inadvertently killed or property inadvertently destroyed in warfare

Language Fallacies

• Emotional or biased language• Equivocation• Ambiguity or obfuscation• Euphemism or PC language• Doublespeak• Pretentious language• Bureaucratic language• Jargon

Impediments to Logic, Good Reasoning, and Critical Thinking

• LOYALTY – loyalty to our own community or group; see its beliefs as more favorable than others

• PROVINCIALISM – narrowing our view to identify with ideas and interests ofonly our own group

• THE HERD INSTINCT – keeping our beliefs and actions within society’s (or our community’s) boundaries

• BACKGROUND BELIEFS• PREJUDICE AND STEREOTYPING• SCAPEGOATING – problems blamed on a person/group• PARTISAN MINDSET – “us” vs. “them”• SUPERSTITIOUS BELIEFS• WISHFUL THINKING AND SELF-DECEPTION• RATIONALIZATION – ignore evidence to justify actions • SUPPRESSION – avoiding the anxiety of stressful thoughts• DENIAL – change our view of the facts of the situation to be more positive

in spite of evidence• LACK OF A SENSE OF BALANCE OR PRUDENCE

SUCCESSFUL ARGUMENTSpersuade the reader by means of:

• Clear premises and conclusions• Evidence, not unsupported claims and appeals to

emotions• Consideration of the other side• Consideration of audience to whom argument is

given• Use appropriate tone and diction• Avoidance of logical fallacies

EVALUATING EVIDENCEIN AN ARGUMENT

• Is the evidence:• SUFFICIENT• REPRESENTATIVE• RELEVANT• ACCURATE• FAIR AND BALANCED

Argument: The Toulmin Model• Claim: Main point or central message; thesis statement

• Support: Data, evidence, reasons, details

• Warrant: Underlying assumptions implied but not stated. Reader infers assumptions.

Warrants are based on:– Authority: respect for credibility and trustworthiness of source– Substance: reliability of facts and evidence– Motivation: values and beliefs of audience and writer

• “The object of reasoning is to find out, from the consideration of what we already know, something else which we do not know.” -- Charles Sanders Peirce

• “A simple person believes every word he hears; a clever one understands the need for truth.” – Proverbs 14:15

• “Those who do not remember the past are condemned to relive it.” --- George Santayana• (One government official to another): “Congratulations Dave! I don’t think I’ve read a more

beautifully evasive and subtlely misleading statement in all my years in government.” – cartoon in the New Yorker by Stevenson

• “Read not to contradict and confute, nor to believe and take for granted … but to weigh and consider.” – Francis Bacon

• “Ignorance of reality provides no protection from it.” – Harold Gordon• “Every man is encompassed by a cloud of comforting convictions, which move with him like flies on

a summer day.” – Bertrand Russell• “Arguments, like men, are often pretenders.” – Plato • “There are lies, damn lies, and statistics.” – Benjamin Disraeli• “Every dogma has it’s day.” – Abraham Rotstein• “Nothing is so firmly believed as what we least know.” – Montaigne • “Populus vult decipi.” (The people want to be deceived.) – Ancient Roman saying• “Logic is only the beginning of wisdom.” -- Spock, Star Trek V, The Undiscovered Country• "If I release a hammer on a positive gravity planet, I do not have to watch it to know that it will

fall." – Spock, Star Trek TV seriies, episode “The Court Martial”• “When an idea is wanting a word can always be found to take its place.” – Goethe• “He who defines the terms wins the argument.” – Chinese proverb• “There is no expedient to which a man will not resort to avoid the real labor of thinking.” – Sir

Joshua Reynolds• “There are no dull subjects. There only dull writers.” -- H. L. Mencken• “Advertising is legalized lying.” – H.G. Wells

Works Cited and Works Consulted• Copi, Irving M. and Carl Cohen. Introduction to Logic, 10th ed.

Upper Saddle River, NJ: Prentice Hall, 1998.

• DeVry/Alpharetta Coll 147/149 Resource Notebook. General Education Department. Alpharetta, GA: DeVry University, 2004.

• Hodges, John C. & Mary Whitten. Harbrace College Handbook, 10th ed. New York: HBJ, 1986.

• Kahane, Howard and Nancy Cavender. Logic and Contemporary Rhetoric: The Use of Reason inEveryday Life. Belmont, CA: Wadsworth/ThomsonLearning, 2002.

• Troyka, Lynn Quitman. Simon & Schuster Handbook forWriters, 5th ed. Upper Saddle River, NJ: PrenticeHall, 1999.