Thinking Critically

Reasoning

Karen S. Wright

Induction is the process of reasoning from facts or instances and arriving at a general claim. Situation: You go to an Arizona Vehicle Center to renew your driver’s license.

You stand in line two hours to get your document.

Later you return for new license plates; clerk gives you wrong advice; you stand in line three hours.

A third time you go there in response to a letter asking for information, and you discover that you need your car registration form, but the letter failed to tell you.

You conclude that the AZ Motor Vehicle Center is inefficient.

You have arrived at this conclusion by induction.

Deductive reasoning moves from the general to the specific.

Several visits to the AZ Motor Vehicle Center were unproductive.

They convince you that the AZ Motor Vehicle Center cares little about the convenience of its patrons.

You will not be happy the next time you must return.

Using Deductive Reasoning

Deductive reasoning might go something like this:

• The AZ Motor Vehicle Center wastes people’s time.

• I have to go to the AZ Motor Vehicle Center tomorrow.

• Therefore, tomorrow my time will be wasted.

You reached this conclusion by means of deduction.

Syllogism

• Deductive arguments have threeparts: two premises and a conclusion.

• This three-partstructure is known as a syllogism.

• The argument is valid whenthe conclusion LOGICALLY follows the premises.

Valid and Invalid ReasoningThe following argument is valid:Premise 1 When it snows, the streets

get wet. (fact)Premise 2 It is snowing (fact)Conclusion Therefore, the streets are wet.The following argument is invalid:Premise 1 When is snows, the streets

get wet. (fact)Premise 2 The streets are wet.Conclusion Therefore, it is snowing. The invalid argument has acceptable premises because

the premises are facts. The argument’s conclusion is wrong. It ignores other reasons why the streets may be wet.

Valid and Invalid ArgumentsWhy is the following invalid?Premise 1 When the battery is

dead, a car will not start.

Premise 2 My car will not start.ConclusionMy battery is dead.

Why is the Following Valid?

Premise 1: When unemployment rates rise, an economic recession occurs.

Premise 2: The unemployment has risen.

Conclusion: An economic recession will occur.

The argument is valid. The writer of the argument must support the claim that the first premise is true.

Inductive Reasoning

Deductive Reasoning

Argument begins With specific evidence

With a general claim

Argument concludes

With a general claim

With a specific statement

Conclusion is Reliable or unreliable

True or false

Reasoning is used To discover something new

To apply what is known

Comparison of Inductive and Deductive Reasoning

Recognizing and Avoiding Logical Fallacies

Logical fallacies are flaws In reasoningthat lead to illogical statementsThat SEEM logical. They masquerade as reasonablestatements. They manipulate readers byappealing to their emotions. Most logical fallacies are known by

labels to indicate where reasoning has gone wrong in the thinking process.

Hasty Generalization• Hasty generalization—when someone

generalizes from inadequate evidence.• “My hometown is the best place to live

in the state” - - generalization is hasty with only two examples of why it is pleasant.

• Stereotyping—a type of generalization that occurs if when someone makes prejudiced, sweeping claims about all members of a particular group.

• Sexism—a type of generalization that occurs when someone discriminates based on sex.

Self-contradiction

• Self-contradiction occurs when two premises are used that cannot simultaneously be true.

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

Guilt by association

• Guilt by association implies that an individual’s argument, ideas, or opinions lack merit because of that person’s activities, interest, or associates.

• “Matilda, who is running for mayor, belongs to the International Hill Climbers Association, which declared bankruptcy last month.”

Card-Stacking

• Ignores evidence on the other side of a question.• Television commercials use this strategy.When three slim, happy customers rave about a newdiet plan, they do not mention that

a) the plan does not work for everyone andb) other plans work better for some people.

The makers of the commercial select evidence topromote their cause.

Taking Something Out of Context

• Taking something out of context separates an idea or fact from the material surrounding it, thus distorting it for special purposes.

• A movie critic writes: “The plot was predictable and boring but the music was sparkling.”

• The advertisement for the movie says, “Critic calls this movie sparkling.”

Appeal to Ignorance• Appeal to ignorance assumes

that the argument is valid simply because it has not been shown to be false.

• Appeals to ignorance can be very persuasive because they prey on people’s lack of knowledge.

• “Since no one has proven that depression does not cause cancer, we can assume it does.”

• The absence of opposing evidence proves nothing.

Ambiguity describes expressions that are not clear because they have more than one meaning.

An ambiguous expression may be taken either way by the reader.

A statement such as “They were entertaining guests” is ambiguous.

Were the guests humorous or were people giving hospitality to guests?

A Complex or Loaded Question

• A complex question contains one or more unproven assumptions.

• “Are you still spending time with known drug addicts?”

Appeal to the People

• Appeal to the people draws on whatever the people hold dear—for example, country, religion, family.

• This approach tries to sway people by using a favorable label instead of sound reasons.

• “A vote for Richard Williams is a vote for the flag.”

Name-calling

• Name calling attaches an unpleasant label to something or someone.

• Name-calling can stop readers from thinking.

• “Gertrude Jones was once an alcoholic, so she cannot possibly say anything of value about politics.”

OH NO!!!!

Think and Write Logically

• Explain how your evidence is clearly.

• Discuss the connection between facts and the inferences they support.

• You must guide your readers and not let them be fooled by confusing or false data.