Good afternoon!

Tomorrow: Background Quiz (PICK UP YOUR QUESTIONS ON

YOUR WAY OUT TODAY!)

Directions O As you go through the slides, fill in the

definitions on the lines in your packet. O You have a test over logical fallacies

Wednesday, April 24th. These notes will be the basis of what you will need to study in order to be successful on the test.

O There is no need to talk, be disruptive, etc. while taking notes unless you have a question. The faster you complete the notes, the sooner we can all move on with our lives!

A fallacy is an error in reasoning.

Some fallacies are so common that they have

names of their own.

Fallacies

SECTION IAppeals to Motives in the Place of Support

The fallacies in this section have in common the practice of appealingto emotions or other psychological factors. In this way, they do not provide reasons for belief.

Ad Misericordiam(Appeal to Pity)

The reader is told to agree to the proposition because of the pitiful state of the author.

OExamples: O How can you say that is out? It was so

close, and besides, I'm down ten games to two.

O We hope you will accept our recommendations. We spent the last three months working extra time on it.

BUY THIS SAD, NEGLECTED KITTY.

Ad Populum(Bandwagon)

O The arguer appeal to the popularity of an idea or of an attitude as a justification.

O Note that voting and majority rule are not so much methods to establish a truth, as a decision procedure that it accepted because it is fair. Truth is not decided by a vote.

Ad Populum ExamplesIf you were beautiful, you could live

like this, so buy Buty-EZ and become beautiful. (Here, the appeal is to the “beautiful people".)

Polls suggest that the Liberals will form a majority government, so you may as well vote for them.

Everyone knows that the Earth is flat, so why do you persist in your outlandish claims?

SECTION IIChanging the

SubjectThe fallacy in this section changes the subject by discussing the person making the argument instead of discussing reasons to believe or disbelieve the conclusion. While on some occasions it is useful to cite authorities, it is almost never appropriate to discuss the person instead of the argument.

Ad HominemAd hominem means, literally, “to the

man”.Ad hominem occurs when, instead of

attacking a person’s position or argument, the arguer attacks the person on irrelevant grounds.

It is the attempt to discredit an idea or proposition by pointing to some flaw or fault in the behavior or character of the person who is the source of the idea or proposition.

Ad Hominem Examples You may argue that God doesn't exist, but you

are just following a fad. We should discount what Premier Klein says

about taxation because he won't be hurt by the increase.

We should disregard Share B.C.'s argument because they are being funded by the logging industry.

After Sally presents an eloquent and compelling case for a more equitable taxation system, Sam asks the audience whether we should believe anything from a woman who isn't married, was once arrested, and smells a bit weird.

Ad Verecundiam(Appeal to Authority)

O Definition: While sometimes it may be appropriate to cite an authority to support a point, often it is not. In particular, an appeal to authority is inappropriate if: O the person is not qualified to have an expert

opinion on the subject,O experts in the field disagree on this issue.O the authority was making a joke, drunk, or

otherwise not being serious O A variation of the fallacious appeal to authority is

hearsay. An argument from hearsay is an argument, which depends on second or third hand sources.

Ad Verecundiam Examples

O Noted psychologist Dr. Frasier Crane recommends that you buy the EZ-Rest Hot Tub.

O "UFOs are not real, because the great Carl Sagan said so."O Economist John Kenneth Galbraith argues that a tight money

policy is the best cure for a recession. (Although Galbraith is an expert, not all economists agree on this point.)

O We are headed for another war. Last week a noted politician remarked that we begin bombing Korea in five minutes.

O My friend heard on the news the other day that Canada will declare war on Serbia. (This is a case of hearsay; in fact, the reporter said that Canada would not declare war.)

SECTION IIIInductive Logic

Inductive reasoning consists of inferring from the properties of a sample to the properties of a population as a whole.

No inductive inference is perfect. That means that any inductive inference can sometimes fail. Even though the premises are true, the conclusion might be false. Nonetheless, a good inductive inference gives us a reason to believe that the conclusion is probably true.

Hasty GeneralizationThe size of the sample is too small to support the conclusion.

O Examples: O Fred, the Australian, stole my wallet. Thus, all

Australians are thieves. (Of course, we should not judge all Australians based on one example.)

O I asked six of my friends what they thought of the new spending restraints and they agreed it is a good idea. The new restraints are therefore generally popular.

SECTION IVFallacy of Ambiguity

This is a case where a word or phrase is used unclearly. This can occur in two ways.•The word or phrase may be ambiguous, in which case it has more than one distinct meaning.•The word or phrase may be vague, in which case it has no distinct meaning.

AccentO Definition: Emphasis is used to suggest

a meaning different from the actual content of the proposition. Accent is a kind of fallacy of ambiguity.

O  Example:  

It would be illegal to give away

FREE BEER!

SECTION VOther Causal Fallacies…

It is common for arguments to conclude that one thing causes another. However, the relation between cause and effect is a complex one. It is easy to make a mistake. In general, we say that a cause C is the cause of an effect E if and only if:

•Generally, if C occurs, then E will occur, and•Generally, if C does not occur, then E will not occur either. We say "generally" because there

are always exceptions, hence the fallacy in logic.

Slippery Slope

In order to show that a proposition P is unacceptable, a sequence of increasingly unacceptable events is shown to follow from P. A slippery slope is an illegitimate use of the "if-then" operator.

Slippery Slope Examples

O If we pass laws against fully automatic weapons, then it will not be long before we pass laws on all weapons, then we will begin to restrict other rights, and finally we will end up living in a communist state. Thus, we should not ban fully automatic weapons.

O You should never gamble. Once you start gambling you find it hard to stop. Soon you are spending all your money on gambling, and eventually you will turn to crime to support your earnings.

Post hoc, ergo propter hoc

O Literally, “after this, therefore because of this”.

O Committing this fallacy occurs when one confuses correlation with causation.

Post hoc, ergo propter hoc Examples

O Immigration to Alberta from Ontario increased. Soon after, the welfare rolls increased. Therefore, the increased immigration caused the increased welfare rolls.

O I took EZ-No-Cold, and two days later, my cold disappeared.

False DilemmaO Giving a limited number of options

when there are in fact more options available.

Examples:O “Either you're for me or against me”.O “America: love it or leave it”.O “Every person is either wholly good or

wholly evil”.

SECTION VIMissing the Point

These fallacies have a general failure to prove that the conclusion is true.

Begging the QuestionO This fallacy occurs when, instead of

giving a reason that establishes the conclusion, the conclusion is simply assumed. The premise is just another way of stating what is supposed to be proved.

O Also known as circular reasoning

Begging the Question Examples

O “Since I'm not lying, it follows that I'm telling the truth.”

O “We know that God exists, since the Bible says God exists. What the Bible says must be true, since God wrote it and God never lies.” (Here, we must agree that God exists in order to believe that God wrote the Bible.)

Sweeping Generalization(Accident)

The fallacy of accident is sometimes also called a sweeping generalization and this latter name for it gives an indication of what is going on. It occurs when a general rule is misapplied to a particular situation.OFor example: The Bible says, "thou shalt not kill", but every time you eat you're killing something.

The End…

Now that that’s over…

You have time to read Animal Farm and work on your study guide.

Remember: Background quiz TOMORROW!