Types of Reasoning

Patterns of inductive reasoning

Argument by Analogy

	The word analogy is derived from the Greek word "analogia" meaning a resemblance or similarity between two things.
	Analogies are based on a similarity, comparison, or precedent.
	"Polar bears at the L.A. zoo live in a cement enclosure that is painted white to resemble snow. That makes about as much sense as painting a picture of an air conditioner on the wall of a person’s apartment."
	The inference being made is that two things which resemble each other in certain known respects will resemble each other in unknown respects.

sample analogy from the movie "Clueless"

So, OK, like right now, for example, the Haitians need to come to America. But some people are all "What about the strain on our resources?" But it's like, when I had this garden party for my father's birthday right? I said R.S.V.P. because it was a sit-down dinner. But people came that like, did not R.S.V.P. so I was like, totally buggin'. I had to haul ass to the kitchen, redistribute the food, squish in extra place settings, but by the end of the day it was like, the more the merrier! And so, if the government could just get to the kitchen, rearrange some things, we could certainly party with the Haitians. And in conclusion, may I please remind you that it does not say R.S.V.P. on the Statue of Liberty?

sample analogies

	Paula Jones’ allegation that she was a victim of sexual harassment by Bill Clinton is comparable to Anita Hill’s allegation of sexual harassment by Clarence Thomas.
	"Life is a sport. Drink it up" (Gatorade slogan)
	If human cloning is allowed to proceed, then Mary Shelley’s fictional work, "Frankenstein" will have become scientific fact.
	Clinton’s use of executive privilege is reminiscent of Richard Nixon and the Watergate scandal.

applications of analogies

	in politics: "domino theory" and Viet Nam
	in advertising: life savings as a "nest egg," computer as a race car,
	in science: "big bang" theory, the brain as a "computer"
	in religion: parables
	analogies in law: case precedent or "stare decisis"
	In economics: natural selection, economic competition leads to the "survival of the fittest."

literal versus figurative analogies

	literal: prohibition didn’t work with alcohol and it won’t work with marijuana
	literal: Mark McGwire is the Roger Maris of the 1990’s.
	figurative: the Viet Nam war and the "domino" effect.
	figurative: the stain on Monica Lewinsky’s dress was the "smoking gun" in the White House sex scandal.

tests of analogies

Are the two things being compared similar in their essential, relevant respects?

Are important dissimilarities being ignored or overlooked?

Have enough points of similarity been drawn?

Are there more dissimilarities than similarities?

Are any points of difference non-critical to the analogy?

Sign Reasoning

Assumes one thing or event is a reliable indicator of another thing or event

signs can be status symbols, economic indicators, political actions, physiological symptoms, or other indices.

effect-to-cause reasoning can also be a form of sign reasoning

example: an MD might rely on symptoms (fever, sore throat) to infer what kind of illness a person has

image: Does the shape of your face offer clues about your personality?

samples of sign reasoning

"The last two times I ate at Coco’s, the same waitress took my order. I think she digs me."

"Babbs may be pregnant. She felt nauseous the past two mornings."

"That guy’s pants are "saggin" and he’s wearing a Raiders jacket, so I’ll bet he’s a gang member."

"It has been 50,000 miles since your car was last serviced. You need a major tune-up."

applications of sign reasoning

in business: economic indicators, inflation rate, consumer confidence, housing starts, unemployment rate

in advertising: associating products with status, prestige, elitism

in medicine: symptoms, fever, dizziness, blood pressure

in religion: 666, signs of the apocalypse

in law: circumstantial evidence; motive, opportunity

image: Can doodles provide insights into your personality?

fallible versus infallible signs

fallible: The Denver Broncos, an AFC team, won the Superbowl, so the stock market will decline this year.

fallible: An Olympic athlete tested positive on a drug test, so he or she must be a drug user.

fallible: Where there is smoke, there is fire.

infallible: fingerprints or genetic markers as proof of one’s identity.

tests of sign reasoning

How reliable or consistent is the sign?

Is the sign fallible or infallible?

Is the sign ambiguous (could it signify something else?)

Is the sign relevant (could it signify nothing?)

Are there a sufficient number of signs?

Are there negative or contradictory signs?

Generalization

Generalizations are one of the most common forms of reasoning.

Generalizing involves attempts to identify general patterns, gauge what is typical or average, or formulate general rules

Generalizing is necessary, indispensable

Imagine what life would be like if you couldn’t form generalizations--if all knowledge was particularized and fragmented.

Generalizing is also fraught with risks

Think how many false stereotypes people hold about race, gender, age, etc.

Identify the generalization embodied in each of the following "light bulb" jokes

How many yuppies does it take to change a light bulb?

One to go buy a designer bulb, and another to make the café lattes.

How many Jewish mothers does it take to change a light bulb?

Don’t worry about me, I’ll just sit here in the dark.

How many liberals does it take to change a light bulb?

None. It is society that needs to change.

How many feminists does it take to change a light bulb?

One! And that’s not funny!

How many politicians does it take to change a light bulb.

A dozen staffers, after which the politician will declare it "a beacon of hope for the future."

How many Americans does it take to change a light bulb?

One to hire a minimum wage worker, and one to file a product liability suit against the light bulb manufacturer.

How many frat guys does it take to change a light bulb?

Ten. One to hold the light bulb, while the other nine drink until the room spins.

How many psychiatrists does it take to change a light bulb?

One, but the light bulb has to want to change.

How many real men does it take to change a light bulb?

None. Real men aren’t afraid of the dark.

universal and statistical generalizations

Universal generalization: claims that all members of a group have certain attributes or characteristics

all men ever think about is sex.

honesty is always the best policy.

Republicans are pro-life, Democrats are pro-choice.

Statistical generalization: claims that a percentage or a portion of a group has a certain attribute or property.

76% of felons are recidivists

the majority of Americans favor legalizing assisted suicide

one out of three children in the United States is born out of wedlock

inductive and deductive generalizations (not synonymous with "deduction" as the term is used in formal logic)

Two types of generalizations: inductive and deductive

Inductive Generalization: bases a larger inference on an example, sample, or particular instance (reasoning from the part to the whole)

example: Babbs bought a Saturn and it runs well. Biff bought a Saturn and it runs well. I guess Saturns are reliable cars.

example: First there was Jennifer Flowers, then Paula Jones, then Kathleen Willie, then Monica Lewinsky. Let’s face it, Clinton is a philanderer.

inductive and deductive generalizations

Deductive Generalization: proceeds from a general rule or general principle to a specific case (reasoning from the whole to the part)

example: Brazilians love soccer. Hector is from Brazil, so he probably loves soccer too.

example: Don’t give money to that vagrant. They are all winos and drug addicts.

example: Biff is a Republican, so of course he’ll vote for the Republican nominee in the next election.

tests of generalizations

How valid or reliable is the "general rule"?

Is the sample from which the generalization is drawn random, and representative?

Is the sample from which the generalization is drawn sufficient? (sample size)

Are there any exceptions to the rule?

Does the general rule is true apply in this particular case?

Reasoning by Example

A sub-set of inductive generalizations (a sample of one)

Offers a generalization based on one or more cases to other cases which are presumed to share the same features as the example.

Examples may be based on personal experience, hearsay, anecdotes, or case studies

example: deciding whether to take a class, see a movie, or eat at a particular restaurant based on a friend’s say so.

sample examples

Our society cherishes the elderly. Look at all the attention surrounding John Glenn’s trip aboard the space shuttle.

Folks who live in Wyoming are homophobic. Matthew Shepard, an avowed gay college student, was beaten to death in Laramie on October 7, 1998.

Athletes’ salaries are out of control. Mike Piazza signed with the N.Y. Mets for $91 million over 7 seasons, Shaq O’Neal signed with the Lakers for $120 million.

tests of examples

Is the example relevant or germane?

How typical or representative is the example?

Watch out for hand-picked examples

Do the examples cover a critical period of time?

Are there enough examples to prove the case?

Are there any negative or contradictory examples?

	Are the two things being compared similar in their essential, relevant respects?
	Are important dissimilarities being ignored or overlooked?
	Have enough points of similarity been drawn?
	Are there more dissimilarities than similarities?
	Are any points of difference non-critical to the analogy?

	Assumes one thing or event is a reliable indicator of another thing or event
	signs can be status symbols, economic indicators, political actions, physiological symptoms, or other indices.
	effect-to-cause reasoning can also be a form of sign reasoning
	example: an MD might rely on symptoms (fever, sore throat) to infer what kind of illness a person has

	"The last two times I ate at Coco’s, the same waitress took my order. I think she digs me."
	"Babbs may be pregnant. She felt nauseous the past two mornings."
	"That guy’s pants are "saggin" and he’s wearing a Raiders jacket, so I’ll bet he’s a gang member."
	"It has been 50,000 miles since your car was last serviced. You need a major tune-up."

	in business: economic indicators, inflation rate, consumer confidence, housing starts, unemployment rate
	in advertising: associating products with status, prestige, elitism
	in medicine: symptoms, fever, dizziness, blood pressure
	in religion: 666, signs of the apocalypse
	in law: circumstantial evidence; motive, opportunity

	fallible: The Denver Broncos, an AFC team, won the Superbowl, so the stock market will decline this year.
	fallible: An Olympic athlete tested positive on a drug test, so he or she must be a drug user.
	fallible: Where there is smoke, there is fire.
	infallible: fingerprints or genetic markers as proof of one’s identity.

	How reliable or consistent is the sign?
	Is the sign fallible or infallible?
	Is the sign ambiguous (could it signify something else?)
	Is the sign relevant (could it signify nothing?)
	Are there a sufficient number of signs?
	Are there negative or contradictory signs?

	Generalizations are one of the most common forms of reasoning.
	Generalizing involves attempts to identify general patterns, gauge what is typical or average, or formulate general rules
	Generalizing is necessary, indispensable
	Imagine what life would be like if you couldn’t form generalizations--if all knowledge was particularized and fragmented.
	Generalizing is also fraught with risks
	Think how many false stereotypes people hold about race, gender, age, etc.

	How many yuppies does it take to change a light bulb?
	One to go buy a designer bulb, and another to make the café lattes.
	How many Jewish mothers does it take to change a light bulb?
	Don’t worry about me, I’ll just sit here in the dark.
	How many liberals does it take to change a light bulb?
	None. It is society that needs to change.
	How many feminists does it take to change a light bulb?
	One! And that’s not funny!
	How many politicians does it take to change a light bulb.
	A dozen staffers, after which the politician will declare it "a beacon of hope for the future."
	How many Americans does it take to change a light bulb?
	One to hire a minimum wage worker, and one to file a product liability suit against the light bulb manufacturer.
	How many frat guys does it take to change a light bulb?
	Ten. One to hold the light bulb, while the other nine drink until the room spins.
	How many psychiatrists does it take to change a light bulb?
	One, but the light bulb has to want to change.
	How many real men does it take to change a light bulb?
	None. Real men aren’t afraid of the dark.

	*Universal generalization*: claims that all members of a group have certain attributes or characteristics
	all men ever think about is sex.
	honesty is always the best policy.
	Republicans are pro-life, Democrats are pro-choice.
	*Statistical generalization*: claims that a percentage or a portion of a group has a certain attribute or property.
	76% of felons are recidivists
	the majority of Americans favor legalizing assisted suicide
	one out of three children in the United States is born out of wedlock

	Two types of generalizations: inductive and deductive
	Inductive Generalization: bases a larger inference on an example, sample, or particular instance (reasoning from the part to the whole)
	example: Babbs bought a Saturn and it runs well. Biff bought a Saturn and it runs well. I guess Saturns are reliable cars.
	example: First there was Jennifer Flowers, then Paula Jones, then Kathleen Willie, then Monica Lewinsky. Let’s face it, Clinton is a philanderer.

	Deductive Generalization: proceeds from a general rule or general principle to a specific case (reasoning from the whole to the part)
	example: Brazilians love soccer. Hector is from Brazil, so he probably loves soccer too.
	example: Don’t give money to that vagrant. They are all winos and drug addicts.
	example: Biff is a Republican, so of course he’ll vote for the Republican nominee in the next election.

	How valid or reliable is the "general rule"?
	Is the sample from which the generalization is drawn random, and representative?
	Is the sample from which the generalization is drawn sufficient? (sample size)
	Are there any exceptions to the rule?
	Does the general rule is true apply in this particular case?

	A sub-set of inductive generalizations (a sample of one)
	Offers a generalization based on one or more cases to other cases which are presumed to share the same features as the example.
	Examples may be based on personal experience, hearsay, anecdotes, or case studies
	example: deciding whether to take a class, see a movie, or eat at a particular restaurant based on a friend’s say so.

	Our society cherishes the elderly. Look at all the attention surrounding John Glenn’s trip aboard the space shuttle.
	Folks who live in Wyoming are homophobic. Matthew Shepard, an avowed gay college student, was beaten to death in Laramie on October 7, 1998.
	Athletes’ salaries are out of control. Mike Piazza signed with the N.Y. Mets for $91 million over 7 seasons, Shaq O’Neal signed with the Lakers for $120 million.

	Is the example relevant or germane?
	How typical or representative is the example?
	Watch out for hand-picked examples
	Do the examples cover a critical period of time?
	Are there enough examples to prove the case?
	Are there any negative or contradictory examples?