Download ppt - BBI 3420 / 3436 ARGUMENTS: Deduction and Induction

BBI 3420 / 3436ARGUMENTS: Deduction and Induction

Overview

• Examining deductive and inductive arguments.

• Telling the difference between the two.

• Different kinds of each argument form.

• Types of fallacies

Types of arguments

• Deductive arguments

• An argument in which it is impossible for a conclusion to be false if its premises are true.

• Inductive arguments

• An argument in which it is improbable for the conclusion to be false if its premises are true.

Deductive Reasoning•Starts with a general rule (a premise) which we know to be true. Then, from that rule, we make a true conclusion about something specific.

Deductive Reasoning• The process of reasoning from known facts to conclusions.

When you reason deductively, you can say “therefore” with

certainty. If your facts were firm to begin with, then your

conclusions will also be firm.

• The conclusion claims to follow necessarily from the premises.

• Example:

• Socrates is a man.

All men are mortal.

Therefore, Socrates is mortal.

•

A deductive argument

• is one in which it is impossible for the premises to be true but the conclusion false.

• It is supposed to be a definitive proof of the truth of the claim (conclusion). • Premise All men are mortal. • Premise Socrates was a man.• Conclusion Socrates was mortal.

• If the premises are true (and they are), then it simply isn't possible for the conclusion to be false.

• If you have a deductive argument and you accept the truth of the premises, then you must also accept the truth of the conclusion.

Deductive Reasoning Is…• Deductive reasoning is when you start from things you

assume to be true, and draw conclusions that must be true if your assumptions are true.

For Example

All dogs have a tail.

Benji is a dog.

Therefore Benji has a tail.

A deductive argument

True Premise

True Premise

True Conclusion

Deductive Reasoning•Example:

•Smith owns only blue pants and brown pants. Smith is wearing a pair of pants today. So, Smith is wearing either blue or brown pants today.

Say this Not this

Gravity makes things fall. The apple that hit my head was due to gravity.

The apple hit my head. Gravity works!

They are all like that -- just look at him!

Look at him. They are all like that.

Toyota make wonderful cars. Let me show you this one.

These cars are all wonderful. They are made by Toyota, it seems.

There is a law against smoking. Stop it now.

Stop smoking, please.

•Who is known for using Deductive Reasoning?

Sherlock Holmes

• Sherlock Holmes would use deductive reasoning to help solve crimes.

Andrew Ault

Example:

Sherlock Holmes could help solve a mystery by making inferences. If Holmes saw a pack of cigarettes by a victim (the victim did not smoke), Holmes can make the assumption that the killer is a smoker.

However…• Deductive reasoning may not be the most accurate way of

solving a problem, cause we all know that assumptions can be wrong.

Other faults of deductive reasoning

All Graduates of M.I.T. are Engineers

George is not from M.I.T.

Therefore George is not an Engineer

Everybody from Texas is a cowboy

Scott is from Texas

Scott is a cowboy

What professions do you think commonly use Deductive

Reasoning?

Why?

• These professions tend to ask a lot of questions to try to solve problems or to prove a point.

• Often they would have to make assumptions to solve problems.

• They would use rules and widely accepted beliefs to prove their argument.

An attorney states that his client is innocent because the crime victim was hit by a car. Since his client does not have a license. He can deduce that his client is innocent.

Deductive Reasoning

Deductive ReasoningFrom vague

To specific

Inductive Argument• The process of going from observations to conclusions.

• This type of conclusion is sometimes called an inference.

• Conclusion claims to follow probably from the premises.

• Example:• Socrates was Greek.

Most Greeks ate fish.

Therefore, Socrates probably ate fish.

Inductive Reasoning•Observing that something is true many times, then concluding that it will be true in all instances

•Using the data to make a prediction

Inductive Reasoning

Inductive ReasoningFrom specific

To vague

An inductive argument• is one in which the premises are supposed to support the

conclusion.• If the premises are true, it is unlikely that the conclusion is

false. • The conclusion probably follows from the premises.

• Premise Socrates was Greek.• Premise Most Greeks eat fish.• Conclusion Socrates ate fish.

• Even if both premises are true, it is still possible for the conclusion to be false (maybe Socrates was allergic to fish).

• Words which tend to mark an argument as inductive include probably, likely, possibly and reasonably.

A inductive argument

True Premise

True Premise

ProbablyTrue

Conclusion

Inductive Reasoning•Example:

•January has been cold here in Siberia. Today is January 14, so it is going to be another cold day in Siberia.

Say this Not thisLook at how those people are behaving. They must be mad.

Those people are all mad.

All of your friends are good. You can be good, too.

Be good.

The base costs is XXX. The extras are XXX, plus tax at XXX. Overall, it is great deal at YYY.

It will cost YYY. This includes XXX for base costs, XXX for extras and XXX for tax.

Deductive Argument

• Premise: Everything made of copper conducts electricity.

• Premise:

This wire is made of copper.

•Conclusion: This wire will conduct electricity.

Weaknesses in Inductive Reasoning

There are two possible weaknesses in inductive generalizations.

1) the sample may not be representative of the population it is drawn from.

Is the sample representative?

2) The sample may be too small, and thus there is a second question we should ask:

Is the sample large enough?

If the sample is unrepresentative or too small then the premises will be inadequate to support the conclusion.

Weaknesses in Inductive Reasoning

Sampling: Examples• Just one observation of the effect of cold metal on a

human tongue is enough for most kids to form a good generalization.

• Similarly, we need not observe the case history of every smoker who has ever lived in order to conclude that smoking is a health hazard.

• On the other hand, someone who concludes that “all the good ones are taken” on the basis of two bad dates might sensibly be advised to keep looking.

Inductive argument

• The local branch of Wachovia Bank was robbed yesterday. Jenny needed money to pay off her gambling debts. She just bought a gun two days ago, and I saw her hanging around the local Wachovia Bank yesterday morning. Today the bookie’s goons stopped looking for Jenny. So Jenny robbed Wachovia Bank yesterday.

Deductive Argument

•Premise: All turtles have shells.

•Premise: The animal I have captured is a turtle.

•Conclusion: I conclude that the animal in my bag has a shell.

Deductive Argument

Sherlock Holmes and Watson were on a camping trip. They had gone to bed and were lying there looking up at the sky. Holmes said, “Watson, look up. What do you see?”

“I see thousand of stars.”

“And what does that mean to you?”

“I guess it means we will have another nice day tomorrow. What does it mean to you, Holmes?”

“To me, it means someone has stolen our tent.”

• Deductive reasoning drives you to a conclusion based on known facts.

Inductive argument• Premise: Tonya is seen

walking from her car to her home with a set of golf clubs.

• Premise: Tonya’s husband Jeff loves golf and tomorrow is his birthday.

• Conclusion: Tonya has bought the set of golf clubs for Jeff.

• Inductive reasoning depends on human observation.• Tonya, after all, may be borrowing the golf clubs. Or

she may have taken up golf herself! • You wouldn’t know unless you observed carefully,

and even then, you would have to describe your conclusion as “probable” but not firm.

Deductive argument

The cut-off date for swim camp registration is June 15. After that date, applicants go on a wait list - no exceptions allowed.

You have missed the cut-off to date to register by two days.

You won’t be registered and your name will go on the waiting list.

How do we tell inductive from deductive?

• The distinction between inductive and deductive arguments is based on the strength of an argument’s inferential claim.• An inferential claim is based on a certain reasoning process – it is the

relationship between the premises and conclusion of an argument.

• But the strength of a claim is hardly ever stated outright, so we have to evaluate it.• Three criteria for measuring an argument’s strength:

• 1) The occurrence of special indicator words.• 2) The actual strength of the inferential link between the premises and conclusion.• 3) The form of argumentation used by the person making the argument.

• Certain indicator words lean more towards inductive and some lean towards deductive. But they’re not always accurate. Pay attention to the context of the argument.• Example: The word “probably” tends to be used in inductive arguments, and

words like “therefore” and “necessarily” tend to lean towards deductive arguments.

Nadia is a B.A (English) student.Most B.A. (English) students own laptops.

So, probably Nadia owns a laptop.

The indicator word test asks whether there are any indicator words that provide clues whether a deductive or inductive argument is being offered.

Common deduction indicator words include words or phrases like necessarily, logically, it must be the case that, and this proves that.

Common induction indicator words include words or phrases like probably, likely, it is plausible to suppose that, it is reasonable to think that, and it's a good bet that.

In the example above, the word probably shows that the argument is inductive.

The Indicator Word Test

No Texans are architects.No architects are Democrats.So, no Texans are Democrats.

The strict necessity test asks whether the conclusion

follows from the premises with strict logical necessity. If

it does, then the argument is deductive.

In this example, the conclusion does follow from the

premises with strict logical necessity. Although the

premises are both false, the conclusion does follow

logically from the premises, because if the premises

were true, then the conclusion would be true as well.

The Strict Necessity Test

Forms of deductive arguments• Argument based on mathematics

• The conclusion depends on a mathematical or geometric measurement.• Has to be deductive since it follows necessarily --- meaning there’s no

room for it “probably” being right. • Example: 1+1 = 2

• There’s no room for a different answer by reevaluating the argument. 1 + 1 will always equal 2. If you have 1+1, then it’ll always equal 2.

• Argument from definition• The conclusion is claimed to depend on the definition of a word or phrase

used either in a premise or in the conclusion.• They follow necessarily because the argument depends completely on the

definition of the word being used.• Example: John is a kleptomaniac, so it follows forth that he steals things.

• The argument is deductive since the definition of the word leads the argument to one conclusion alone.

More deductive forms• Categorical syllogisms

• A 3-line argument. Made up of exactly two premises and one conclusion. Begin with the words “all”, “some”, and “no”.

• Example:• All oaks are trees*• All trees are plants• All oaks are plants .

• Hypothetical Syllogisms• Syllogisms (two premises and one conclusion) that have a conditional statement for one (or both)

of its premises.• Example:

• If it rains, we will not have a picnic.• If we don't have a picnic, we won't need a picnic basket.• Therefore, if it rains, we won't need a picnic basket.

• If you have A, then you have B.• If you have B, then you have C.• Therefore, if you have A, then you have C.

• .

Hypotheticals work like chains…one leads to the next and ties them all together

Inductive argument forms• Prediction

• An argument that works based off our knowledge of the past in order to make a claim about the future.• Example:

• There tends to be a lot of rain in the Midwest, so it will probably rain there tomorrow.

• Claims about the future can’t be known with any certainty, so they can’t be absolutely true, even though they can be justified. That makes them inductive.

• Argument from analogy• Depends on the existence of an analogy (or similarity) between two

separate things.• Example:

• My Honda gets good gas mileage.

• So it follows that John’s Honda also gets good gas mileage.

• The truth of an argument like this is based on chance, so and that chance makes it an inductive argument.

More inductive argument forms• Generalization

• An argument that is applied to a whole group based on knowledge gained from a small sample of people.• Example:

• Five out of ten people in Ellis Hall said they support abortion. So I can say that half of Athens supports abortion.

• Statistical data is not always accurate, so the truth of this form of argument can not be made certain. It remains only probable.

• Argument from authority• An argument that concludes something is true because an expert said it

is.• Example:

• Centrum vitamins work because Dr. Jones did a study that proved it.

• This type of argument is only true with probability since studies can be wrong or mistaken.

Even more inductive argument forms

• Argument based on signs• Conclusion based on knowledge gained from a sign about what the

sign claims to mean.• Example:

• A sign on the side of the road says “School Zone” so I can assume that a school is somewhere up ahead.

• The sign could have been moved from somewhere else, or it could simply be wrong, so it can’t be true with absolute certainty.

• Causal inference• Argument that proceeds from knowledge of a cause to a claim

about its effect, or vice versa, that knowledge of an effect can provide information about its cause.• Example:

• I left a soda in the freezer last night, so I can assume that it is frozen.

All bats are mammals.All mammals are warm-blooded.So, all bats are warm-blooded.

Deductive.

If the premises are true, the conclusion, logically, must also

be true.

Is the argument below deductive or inductive?

Tess: Are there any good Italian restaurants in town?

Don: Yeah, Luigi's is pretty good. I've had their Neapolitan rigatoni, their lasagne col pesto, and their mushroom ravioli. I don't think you can go wrong with any of their pasta dishes.

Is this argument deductive or inductive? How can you tell?

Inductive.

The argument is an inductive generalization, which is a common pattern of inductive reasoning. Also, the conclusion does not follow with strict necessity from the premises.

I wonder if I have enough cash to buy my psychology textbook as well as my biology and history textbooks. Let's see, I have $200. My biology textbook costs $65 and my history textbook costs $52. My psychology textbook costs $60. With taxes, that should come to about $190. Yep, I have enough.


Deductive.

This argument is an argument based on mathematics,which is a common pattern of deductive reasoning. Plus,the conclusion follows necessarily from the premises.

Mother: Don't give Billy that brownie. It contains walnuts, and I think Billy is allergic to walnuts. Last week he ate some oatmeal cookies with walnuts, and he broke out in a severe rash.

Father: Billy isn't allergic to walnuts. Don't you remember he ate some walnut fudge ice cream at Melissa's birthday party last spring? He didn't have any allergic reaction then.

Is the father's argument deductive or inductive? How can

you tell?

Mother: Don't give Billy that brownie. It contains walnuts, and I think Billy is allergic to walnuts. Last week he ate some oatmeal cookies with walnuts, and he broke out in a severe rash.

Father: Billy isn't allergic to walnuts. Don't you remember he ate some walnut fudge ice cream at Melissa's birthday party last spring? He didn't have any allergic reaction then.

Inductive.

The father's argument is a causal argument, which is acommon pattern of inductive reasoning. Also, theconclusion does not follow necessarily from thepremises. (Billy might have developed an allergic reaction to walnuts since last spring.)

John is an agnostic. It necessarily follows that he doesn't believe in God.


Deductive.

This argument is an argument by definition, which is acommon pattern of deductive inference. Also, the phrase"it necessarily follows that" is a deduction indicatorphrase. Also, the conclusion follows from the premises.

Larry: Do you think Representative Miller will be re-elected?

Norman: I doubt it. Miller's district has become more conservative in recent years. Miller is a liberal Democrat, and 63% of the registered voters in his district are now Republicans.


Inductive.

This argument is both a statistical argument and a predictive argument, which are two common patterns ofinductive reasoning. Also, the conclusion does not follownecessarily from the premises.

If Buster walked to the game, then he didn't drive to the game. Buster didn't drive to the game.

Therefore, Buster walked to the game.


If Buster walked to the game, then he didn't drive to the game.Buster didn't drive to the game.Therefore, Buster walked to the game.

X

Deductive.

This argument is a hypothetical syllogism, which is acommon pattern of deductive reasoning.

Note, however, that the conclusion does not follow logically from the premises. (Maybe Buster rode his bike to the game, for example.) The argument commits the fallacy of "affirming the consequent."

Evaluating Arguments

• Once you have an argument summarized/standardized, you need to evaluate it to see if you are forced to accept the conclusion.

• There are two main questions to ask when doing so:• Is the argument a “good argument”?• Are the premises acceptable?

When is an argument a good argument?

• What “good argument” does not mean:• “agrees with my views”

• The attitude that only arguments that agree with your viewpoints are good is extremely close-minded.

• “persuasive argument” • People aren’t always smart and can be persuaded by

“eloquent speech” (and be confused by solid reasoning). • Hitler was more persuasive than Churchill, but that doesn’t

mean that Hitler’s arguments were better. • “well-written/spoken”

• Although it’s easier to tell whether an argument is good if it is well written, being well written doesn’t make it good. Clarity, eloquence and organization can all occur in the presence of logical mistakes.

When is an argument a good argument?

• What “good argument” does mean. • It must, at the least, be either deductively sound (valid with true

premises) or inductively cogent (strong with true premises).• In a nut shell, a good argument embodies all the good

qualities of critical thinking.

When is an argument a good argument?• But it will also need to be clear…

• An argument isn’t good unless it is understandable.

• …precise…• One needs to avoid equivocation and use exact language.

• …the premises need to be relevant…• Arguments with a lot of irrelevant material can’t be said to be good

arguments.

• …consistent…• Arguments that contain logical contradictions commit the fallacy of

inconsistency.

• …complete…• If an arguer ignores facts relevant to the conclusion at hand, we can’t say

the argument is good (it doesn’t account for relevant objections).

• …and fair.• An argument can’t be good if it hastily dismissed objections.


What is a good argument?What is a good argument?

• A good argument (2 conditions) - All premises are true, and the premises provide good reasons to accept the conclusion.

• An argument is deductively valid if the conclusion must be true if the premises are true.

• An argument is inductively strong if the conclusion is probably true if the premises are true.

A good argument, fundamentally, is an argument that is either deductively sound or inductively cogent.

A good argument, fundamentally, is an argument that is either deductively sound or inductively cogent.

What is a good argument?

A A good argument from the standpoint of critical from the standpoint of critical

thinking is:thinking is:

The most important The most important critical thinking standards critical thinking standards areare::

Accuracy – Are all the premises true?– Are all the premises true? Logical Correctness – Is the reasoning correct? Is the – Is the reasoning correct? Is the

argument deductively valid or inductively strong?argument deductively valid or inductively strong? Also, other critical thinking standards must be taken into Also, other critical thinking standards must be taken into

account, including account, including clarity, precision, relevance, clarity, precision, relevance, consistency, completenessconsistency, completeness and and fairnessfairness..

An argument that satisfies the An argument that satisfies the relevant critical thinking standards relevant critical thinking standards that apply in a particular context.that apply in a particular context.

An argument that satisfies the An argument that satisfies the relevant critical thinking standards relevant critical thinking standards that apply in a particular context.that apply in a particular context.

Evaluating ArgumentsEvaluating Arguments

General Guidelines

Are the Are the premises truepremises true?? relevant relevant to the conclusion? to the conclusion?

Is the Is the reasoning correctreasoning correct? Is the argument ? Is the argument deductively validdeductively valid or or

inductively stronginductively strong??

Does the arguer commit any Does the arguer commit any logical fallacieslogical fallacies??

Does the arguer express his or her points Does the arguer express his or her points clearlyclearly and and preciselyprecisely??

Are the arguer’s claims Are the arguer’s claims logically consistentlogically consistent? Do any of the arguer’s ? Do any of the arguer’s

claims claims contradictcontradict other claims made in the argument? other claims made in the argument?

Is the argument Is the argument completecomplete? Is all relevant evidence taken into account ? Is all relevant evidence taken into account

(given understandable limitations of time, space, context and so on)?(given understandable limitations of time, space, context and so on)?

Is the argument Is the argument fairfair? Is the arguer fair in his or her presentation of the ? Is the arguer fair in his or her presentation of the

evidence and treatment of opposing arguments and views?evidence and treatment of opposing arguments and views?

An argument is deductively valid if the conclusion must be true if the premises are true.

An argument is inductively strong if the conclusion is probably true if the premises are true.

Dylan is a man.He is 99 and is in a coma.Therefore, Dylan will not run in the marathon tomorrow.


Example of deductively valid argumentExample of deductively valid argument

All monkeys are primatesAll monkeys are primates

All primates are mammalsAll primates are mammals

So, all monkeys are mammalsSo, all monkeys are mammals

the following argument is not valid:the following argument is not valid:

If Sue misses her plane she will be late for the conference.If Sue misses her plane she will be late for the conference.

Sue is late for the conference.Sue is late for the conference.

Therefore, she missed her plane.Therefore, she missed her plane.

When is it reasonable to accept a premise?

• Arguments always contain premises, and—while some premises

will have support from other premises—there will always be

some premises that are mere assumptions (claims made by the

arguer).

• If the argument is valid/ strong, its soundness/cogency will turn

on whether these assumptions are true. So how can we tell if we

should accept them?

• The Principle of Rational Acceptance


When is it reasonable to accept a premise?When is it reasonable to accept a premise?

In general, it is reasonable to accept andIn general, it is reasonable to accept and unsupported claim as true when:when:

1.1. The claim does not conflict with The claim does not conflict with personal experiencespersonal experiences that that we have no good reason to doubt,we have no good reason to doubt,

2.2. the claim does not conflict with the claim does not conflict with background beliefs / background beliefs / information information that we have no good reason to doubt, andthat we have no good reason to doubt, and

3.3. The claim comes from a The claim comes from a credible sourcecredible source..

The Principle of Rational Acceptance

The Principle of Rational Acceptance


1. Does the Claim Conflict with our Personal Experiences?1. Does the Claim Conflict with our Personal Experiences?

• People often place too much trust in their own observation and experiences.

• Personal experiences are often less reliable than we think. We need to be aware that “believing” is often “seeing” and that things are not always as they appear.

My dog is “as gentle as a kitten.” Got it!

Really?

Critical thinkersCritical thinkers recognize that their beliefs, hopes, fears, expectations, and biases can affect their observations.Critical thinkersCritical thinkers recognize that their beliefs, hopes, fears, expectations, and biases can affect their observations.

Evaluating Arguments1. Does the Claim Conflict with our Personal Experiences?1. Does the Claim Conflict with our Personal Experiences?

• But it should be noted that your senses are not indubitable (un-doubtable). They can be mistaken for any number of reasons.

• Bad physical conditions (e.g., poor lighting)• Sensory impairment (e.g., poor vision)• Observer impairment (e.g., drunk)• Unreliable measuring instruments• Bad memory

• People often place too much trust in their own observation and experiences.• Personal experiences are often less reliable than we think. We need to be aware that “believing” is often “seeing”

and that things are not always as they appear.

How reliable are your senses?

How reliable are your senses?

Evaluating Arguments2. Does the Claim Conflict with our Background Beliefs?2. Does the Claim Conflict with our Background Beliefs?• Background beliefs - Background beliefs - convictions held—usually assumed

without question—that inform most of the other beliefs that we have

This contradicts our background belief that people aren’t robots.

This contradicts our background belief that people aren’t robots.

Sarah Parker is a robot.

But it is important to note that even background beliefs should be subject to revision if sufficient evidence is presented against them (don’t be dogmatic about any beliefs you have) e.g. It snowed in London last July.

It snowed in Las Vegas last July 4th

This seems to contradict our background belief that it doesn’t snow in deserts during the summer

This seems to contradict our background belief that it doesn’t snow in deserts during the summer

ExerciseFor each of the following unsupported claimsunsupported claims, indicate whether or not it

would be reasonable to accept the claim. Also, state the criteria you use in reaching your decision.

Is the claim consistent with my personal experiences?

Is the claim consistent with my background beliefs / convictions?

• Black cats bring bad luck.

• 98% of statistics are just made up.

• I read the entire Encyclopedia Britannica last summer

(said by a stranger at a party).

• There is no hard scientific evidence that smoking is addictive (said by a

tobacco company executive).

• Ghosts really exist.

• Aliens have visited the earth in some form.

3. Does the claim come from a credible 3. Does the claim come from a credible source?source?

Questions to ask to determine source Questions to ask to determine source credibility: credibility: Genuine expert? Genuine expert? Are they outside their area? Are they outside their area? Are they biased? Are they biased? Do they have a reason to lie? Do they have a reason to lie? Questionable senses (were they drunk)? Questionable senses (were they drunk)? Are they generally reliable (is it The Enquirer? ) Are they generally reliable (is it The Enquirer? ) Right context? Right context? Can expert opinion settle the issue (Can expert opinion settle the issue (e.g.,e.g., is this a is this a

moral issue)? moral issue)? Is it improbable? Is it improbable?

3. Does the Claim Come from a Credible Source?

Is the source a Is the source a genuine expert genuine expert or authority?or authority? Does the source speak in his or her Does the source speak in his or her area of area of

expertiseexpertise?? Is the source biased or has some other Is the source biased or has some other motivemotive to to

lie or mislead?lie or mislead? Is the Is the accuracyaccuracy of the source’s personal of the source’s personal

observations or experiences questionable?observations or experiences questionable?


Does the Claim Come from a Credible Source?

Is the source contained in a source that is Is the source contained in a source that is generally generally unreliableunreliable (e.g. gossip magazine) ?(e.g. gossip magazine) ?

Has the source been Has the source been cited correctly cited correctly or has been or has been quoted quoted out of contextout of context??

Is the issue one that Is the issue one that can be settled can be settled by expert by expert opinion?opinion?

Is the claim made by the source highly Is the claim made by the source highly improbableimprobable on its face?on its face?

Critical thinkers must ask, “Are all premises true?” and “Do the premises provide good reasons to accept

the conclusion?”

Critical thinkers must ask, “Are all premises true?” and “Do the premises provide good reasons to accept

the conclusion?”


FallaciesFallacies A form of reasoning that is illogical or violates the A form of reasoning that is illogical or violates the

rules of valid argumentrules of valid argument *hasty generalization*hasty generalization "I have dated three women from FBMK, and they all had tempers. "I have dated three women from FBMK, and they all had tempers.

Therefore, all female students from FBMK have tempers." Therefore, all female students from FBMK have tempers."

This is a hasty generalization because three is not a large This is a hasty generalization because three is not a large enough sample size to accurately determine the temper of all enough sample size to accurately determine the temper of all redheads.redheads.

A generalization based on too little evidence or on exceptional or biased evidence.

Dicto Simpliciter (Sweeping Dicto Simpliciter (Sweeping Generalization)Generalization)

Making a sweeping statement and expecting it to be true in Making a sweeping statement and expecting it to be true in every specific instanceevery specific instance

The result is stereotyping. The result is stereotyping. The problem is that the sweeping statement may be true in The problem is that the sweeping statement may be true in

many cases, but it is not necessarily true in every case. Thus many cases, but it is not necessarily true in every case. Thus the conclusion would be invalid for those exceptions.the conclusion would be invalid for those exceptions.

"Scientists are closed-minded. If something doesn't "Scientists are closed-minded. If something doesn't fit into one of their formulas or laws, they won't even fit into one of their formulas or laws, they won't even consider it as being possible or even be willing to consider it as being possible or even be willing to study it to find out the truth."study it to find out the truth."

Non Sequitur Non Sequitur (It does not follow)(It does not follow)

A statement that does not follow logically from what has A statement that does not follow logically from what has just been said—a conclusion that does not follow from the just been said—a conclusion that does not follow from the premises. premises.

Faulty:Faulty:

Susan is smart; therefore she will receive good Susan is smart; therefore she will receive good grades.( Many smart people do not receive good grades.( Many smart people do not receive good grades.)grades.)

"If you do not buy this type of pet food, you are "If you do not buy this type of pet food, you are neglecting your dog."neglecting your dog."

Caused by invalid deductive reasoningCaused by invalid deductive reasoning

Either ….or Either ….or

The writer states that only two alternatives exist when in fact The writer states that only two alternatives exist when in fact there are more than two. there are more than two.

Faulty:Faulty:

A mother may tell her child: “Eat your broccoli or you A mother may tell her child: “Eat your broccoli or you won’t get desert.”won’t get desert.”

An ignorant friend might say: “I’m not a doctor, but An ignorant friend might say: “I’m not a doctor, but your runny nose and cough tell me that you either your runny nose and cough tell me that you either have a cold or the flu.”have a cold or the flu.”

Caused by invalid deductive reasoningCaused by invalid deductive reasoning

Circular ReasoningCircular Reasoning

Circular reasoning is an attempt to support a statement by Circular reasoning is an attempt to support a statement by simply repeating the statement in different or stronger terms. simply repeating the statement in different or stronger terms. The reason given is nothing more than a restatement of the The reason given is nothing more than a restatement of the conclusion that poses as the reason for the conclusion. conclusion that poses as the reason for the conclusion.

Faulty:Faulty:

A confused student argues: “You can’t give me a C. A confused student argues: “You can’t give me a C. I’m an A student!”I’m an A student!”

An obvious non-smoker blurts: “Can a person quit An obvious non-smoker blurts: “Can a person quit smoking? Of course — as long as he has sufficient smoking? Of course — as long as he has sufficient willpower and really wants to quit.”willpower and really wants to quit.”

BandwagonBandwagon

An argument saying, in effect, An argument saying, in effect, "Everyone's "Everyone's doing or saying or thinking this, so you doing or saying or thinking this, so you should, too.“should, too.“

Faulty:Faulty:Everyone else is drinking, so why Everyone else is drinking, so why shouldn't I?(The majority is not always shouldn't I?(The majority is not always right.)right.)

HominemHominem

Attacking the person who presents an issue Attacking the person who presents an issue rather than dealing logically with the issue itselfrather than dealing logically with the issue itself

Faulty:Faulty:

His arguments might impress us if we were not His arguments might impress us if we were not aware of how he treats his children.aware of how he treats his children. (The man's (The man's alleged unfatherly behavior need not invalidate alleged unfatherly behavior need not invalidate his arguments.)his arguments.)

Red HerringRed Herring

Dodging the real issue by drawing attention to Dodging the real issue by drawing attention to an irrelevant issue.an irrelevant issue.

Faulty:Faulty:

Why worry about a few terrorists when we ought Why worry about a few terrorists when we ought to be doing something about acid rain?to be doing something about acid rain?

Acid raid has nothing to do with the actions of Acid raid has nothing to do with the actions of terrorists.)terrorists.)

Any Questions? Any Questions?

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