Critical Thinking:A User’s Manual

Chapter 6Preparing to Evaluate Arguments

Preparing to Evaluate Arguments

Valid/invalidSound/unsound

Strong/weakCogent/uncogent

Types of Reasoning

Deductive Reasoning: an argument in which the arguer attempts to demonstrate that the truth of the conclusion necessarily follows from the premises.

Inductive Reasoning: an argument in which the arguer attempts to demonstrate that the truth of the conclusion probably follows from the premises.

Deductive or Inductive?

Every philosophy class I have taken has been fun. Therefore, this philosophy class will be fun.

If this is a philosophy class, then it will be fun. It is a philosophy class, therefore it will be fun.

Reasoning Indicators

Inductive Reasoning probable plausible likely reasonable to conclude

Deductive Reasoning certainly absolutely definitely

Deductive or Inductive?

Every philosophy class I have taken has been fun. Therefore, this philosophy class certainly will be fun.

Your Turn!

How can you tell whether or not an argument with a deductive argument indicator is really a deductive argument?

Deductive Arguments

A categorical argument is a deductive argument that contains categorical claims.

A truth-functional argument is a deductive argument that contains truth-functional claims.

Categorical Claims

Universal Affirmative: All S are PAll cats are mammals.

Universal Negative: No S are PNo cats are dogs.

Particular Affirmative: Some S are PSome mammals are cats.

Particular Negative: Some S are not PSome mammals are not cats.

Your Turn!

Provide your own example of each kind of categorical claim.

Truth-Functional Claims

Simple Claim: PIt is raining.

Negation: not PIt is not raining.

Conjunction: P and QIt is raining and clouds are in the sky.

Disjunction: P or QIt is raining or clouds are in the sky.

Conditional: If P, then QIf it is raining, then clouds are in the sky.

Your Turn!

Provide your own example of each kind of truth-functional claim.

Your Turn!

Identify the following as a categorical or a truth-functional claim, and explain your decision.

If all cats are mammals, then no cats are reptiles.

Distinguishing Kinds ofDeductive Arguments

Step 1: Is the passage an argument, explanation or neither?

Step 2: Is the argument deductive or inductive?Step 3: Does the argument have categorical

claims or truth-functional claims?

Categorical or Truth-Functional?

All sportscasters are athletes, and no athletes are college professors. Thus, no sportscasters are college professors.

Either Jim is a sportscaster or he is a college professor. Since he isn’t a sportscaster, he must be a college professor.

Inductive Arguments

An analogical argument is an inductive argument that uses an analogy to show that because one case has a particular feature, the other case should, too.

An inductive generalization is an inductive argument that concludes that some, most, or all of a particular group has some feature based on evidence that a portion of that group has the feature.

A causal argument is an inductive argument that provides evidence that a causal claim is true.

Analogies

A good education is like good health care.Accusing me of being lazy is like the pot calling

the kettle black.Life is like a bowl of cherries.

General Claims

All college freshmen must take general education courses.

Every performance-enhancing drug is banned in the Tour de France.

Herb tea does not contain caffeine.Most cats are domestic pets.

Causal Claims

H1N1 causes serious breathing problems in children with asthma.

You can get a sore back by lifting incorrectly.Increased regulation of banks will prevent

future economic disasters.

Your Turn!

How can you tell whether an argument containing the following conclusion is a categorical argument or an inductive generalization?

All swans are white.

Distinguishing Kinds ofInductive Arguments

Step 1: Is the passage an argument, explanation or neither?

Step 2: Is the argument deductive or inductive?Step 3: Does the argument contain an analogy, a

general claim, or a causal claim?

Analogical, Generalization, or Causal?

Cats are like dogs. Since I am allergic to cats, I am probably also allergic to dogs.

I have had an allergic reaction to every cat I have encountered. Thus, I am likely allergic to all cats.

When my mom visited me last weekend, she had classic symptoms of an allergic reaction. Given that I just adopted a cat, mom’s allergies must have been caused by the cat.

Evaluating Arguments

StructureDo the premises support the conclusion?

TruthAre the premises true?

Evaluating Deductive ArgumentsValidity

Refers to structureIf the premises are true, then the conclusion must

be trueSoundness

Refers to both structure and truthThe argument is valid and the premises are all

true

Your Turn!

Which of the five kinds of arguments that you learned to identify in this chapter are evaluated using the language of validity and soundness?

Evaluating Inductive ArgumentsStrength

Refers to structureIf the premises are true, then the conclusion is

probably trueCogency

Refers to both structure and truthThe argument is strong and the premises are all

true

Your Turn!

Which of the five kinds of arguments that you learned to identify in this chapter are evaluated using the language of strength and cogency?

Preparing to Evaluate Arguments

Valid/invalidSound/unsound

Strong/weakCogent/uncogent

Writing a Complete Analysis

Step 1: Write a Basic Analysis of the passage.Identify the passage.Analyze the passage.

Step 2: If it is an argument, determine whether it commits a fallacy.Identify the fallacy, and explain how it is committed.

Step 3: If it is a non-fallacious argument, diagram it.Verify that your diagram is consistent with your Basic

Analysis.

Writing a Complete Analysis

Step 4: Identify the kind of argument.If the argument is deductive, identify it as a

categorical argument or a truth-functional argument.

If the argument is inductive, identify it as an analogical argument, an inductive generalization, or a causal argument.

If the government of the United States is really built on the notion that all people are fundamentally equal, then every person would be equally treated under the law. It’s clear that not everyone is treated equally, because crimes committed by wealthier individuals result in much lighter sentences than those committed by poor people. So, we must conclude that the government of the United States is not really built on the idea of fundamental equality among persons.

This passage contains an argument. The issue is whether the government of the United States is built on the idea of fundamental equality among persons. The conclusion is that the government of the United States is not really built on the idea of fundamental equality among persons. The first premise is that if the government of the United States is really built on the notion that all people are fundamentally equal, then every person would be equally treated under the law. The second premise is that not everyone is treated equally under the law in the United States.

This passage contains a subargument. The intermediate conclusion is that not everyone is treated equally under the law in the United States. The premise is that crimes committed by wealthier individuals result in much lighter sentences than those committed by poor people.

If the government of the United States is really built on the notion that all people are fundamentally equal, then every person would be equally treated under the law. It’s clear that not everyone is treated equally, because crimes committed by wealthier individuals result in much lighter sentences than those committed by poor people. So, we must conclude that the government of the United States is not really built on the idea of fundamental equality among persons.

+

This passage contains an argument. The issue is whether the government of the United States is built on the idea of fundamental equality among persons. The conclusion is that the government of the United States is not really built on the idea of fundamental equality among persons. The first premise is that if the government of the United States is really built on the notion that all people are fundamentally equal, then every person would be equally treated under the law. The second premise is that not everyone is treated equally under the law in the United States.

This passage contains a subargument. The intermediate conclusion is that not everyone is treated equally under the law in the United States. The premise is that crimes committed by wealthier individuals result in much lighter sentences than those committed by poor people.

This passage is a deductive truth-functional argument.