Critical Thinking: A User

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Critical ThinkingA Users Manual

• Chapter 9
• Evaluating Analogical Arguments

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Analogical 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 analogy is a claim that compares two , or
  more, things.

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Analogies

• Learning is like rowing upstream.
• My love is like a red, red rose.
• Life is a rollercoaster.

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• Cats are like dogs. Since dogs make good pets,
  cats probably make good pets.
• P1
• P2
• Issue

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• ? Cats are like dogs. Since ? dogs make good
  pets, ? cats probably make good pets.

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Anatomy of Analogical Arguments

• P1 (analogy) T is like S
• P2 (feature) S has F
• ? T has F
• S sample
• T target
• F feature

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• Cats are like dogs. Since dogs make good pets,
  cats probably make good pets.
• P1
• P2
• S
• T
• F

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• Both Brenda and Susan live in Orange County,
  have three children in private schools, and drive
  BMWs. Since Brenda is wealthy, Susan probably
  is, too.
• P1
• P2
• P3
• ?
• P1
• P2
• Issue

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• Both Brenda and Susan live in Orange County,
  have three children in private schools, and drive
  BMWs. Since Brenda is wealthy, Susan probably
  is, too.
• S
• T
• F

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• ? Both Brenda and Susan live in Orange County, ?
  have three children in private schools, and ?
  drive BMWs. Since ? Brenda is wealthy, ? Susan
  probably is, too.
• ?

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Evaluating Analogical Arguments

• Analogical arguments may be strong or weak.
• Consider evidence for the analogy
• Consider relevance of the analogy

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Evaluating Evidence for the Analogy

• Sample size
• The more instances in the sample, the stronger
  the argument.
• Quantity of similarities
• The more relevant characteristics shared by the
  sample and target, the stronger the argument.

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Which argument is stronger?

• Brenda and Susan live in Orange County. Since
  Brenda is wealthy, Susan probably is, too.
• Carla, Mary, Brenda, and Susan all live in
  Orange County. Since Carla, Mary, and Brenda are
  wealthy, Susan probably is, too.

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Which argument is stronger?

• Both Brenda and Susan live in Orange County,
  have three children in private schools, and drive
  BMWs. Since Brenda is wealthy, Susan probably
  is, too.
• Both Brenda and Susan live in Orange County.
  Since Brenda is wealthy, Susan probably is, too.

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Evaluating Relevance of the Analogy

• An analogical argument uses a faulty analogy
  whenever the similarities between the sample and
  target are irrelevant to the feature.

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Is the analogy relevant?

• Brenda and Susan have three children. Since
  Brenda is wealthy, Susan probably is, too.

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Complete Analysis plus Evaluation

• 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 nonfallacious argument,
  diagram it.
• Verify that your diagram is consistent with your
  Basic Analysis.

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Complete Analysis plus Evaluation

• 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.

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Complete Analysis plus Evaluation

• Step 5 Evaluate the argument.
• If the argument is categorical, state the
  syllogism in standard form, and demonstrate
  whether the argument is valid or invalid using
  either a Venn diagram or the rules for valid
  syllogisms.
• If the argument is truth-functional, translate
  the argument, and demonstrate whether the
  argument is valid or invalid by identifying the
  argument form, using the truth table method, or
  using the shortcut method.
• If the argument is analogical, evaluate its
  strength by considering the evidence provided for
  the analogy and the relevance of the analogy to
  the feature.

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• An "online affair" is just like an affair in
  person because they both devalue their primary
  partners. Since divorce is the appropriate
  response to an affair in person, it is also an
  appropriate response to an online affair.

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• This passage contains an argument. The issue is
  whether divorce is an appropriate response to an
  online affair. The conclusion is that divorce is
  an appropriate response to an online affair. The
  first premise is that an online affair is like an
  affair in person. The second premise is that
  divorce is an appropriate response to an affair
  in person.
• This passage contains a subargument. The
  intermediate conclusion is that an online affair
  is like an affair in person. The premise is that
  both online affairs and affairs in person devalue
  their partners.

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• ? An "online affair" is just like an affair in
  person because ? they both devalue their primary
  partners. Since ? divorce is the appropriate
  response to an affair in person, ? it is also an
  appropriate response to an online affair.
• ?
• ?
• ? ?
• ?
• ?

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• This passage contains an argument. The issue is
  whether divorce is an appropriate response to an
  online affair. The conclusion is that divorce is
  an appropriate response to an online affair. The
  first premise is that an online affair is like an
  affair in person. The second premise is that
  divorce is an appropriate response to an affair
  in person.
• This passage contains a subargument. The
  intermediate conclusion is that an online affair
  is like an affair in person. The premise is that
  both online affairs and affairs in person devalue
  their partners.
• This passage is an inductive analogical
  argument. The argument is somewhat strong because
  the analogy is relevant to the feature, but there
  is only one similarity to support the analogy and
  only one instance in the sample.