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Critical Thinking By Example

 Chapter 2: Basic Argument Evaluation
  Quiz 2.1 Quiz 2.2 Quiz 2.3 Quiz 2.4 Quiz 2.5

 

Material covered in this chapter

  •     2.1 The definition of a good argument

  •     2.2 Three Fallacies

 

2.1 The Definition of a Good Argument

 A good argument is one that meets these three conditions: (1) The premise set is relevant to the conclusion, (2) the premise set is sufficient for the conclusion, and (3) the premises are acceptable.

 

Example 2.1: A good argument.

[1] All humans are mortal. [2] Socrates is a human. [3] So, Socrates is mortal.

 

The premises [1] and [2] are acceptable, since they are true. The premises are relevant to the conclusion [3] and sufficient, so this is a good argument.

 

2.2 Three Fallacies

 

It may help to understand the definition of a good argument by considering bad arguments, that is, arguments that fail to meet one of the three conditions for a good argument. We will define three fallacies, characteristic ways people make bad arguments, to illustrate failure of each conditions.

 

Fallacy of Irrelevant Reason

 

Definition: An argument contains this fallacy if the premise set is irrelevant to the question of whether we should accept the conclusion.

Note: example 2.2 is purposely ridiculous to exemplify the underlying pattern. Even though the premise is true, it provides us no reason to believe that the conclusion is true. The premise is irrelevant to the conclusion. Most arguments that commit the fallacy of irrelevant reason are more subtle than this, but the underlying pattern is the same.

 

Example 2.2: An argument that commits the fallacy of Irrelevant Reason

P1: Some people are worried about the fate of polar bears with the melting of the arctic ice.
C: Therefore, all polar bears are white.

Fallacy of Hasty Conclusion: An argument contains this fallacy if the premise set is insufficient to warrant the acceptance of the conclusion.

 

The conclusion is hasty because even if the premise is acceptable it does not provide sufficient support for the conclusion. The premise does not address the question of the color of polar bears that are not in the zoo. In other words, a good argument for the conclusion would include evidence about the color of polar bears wherever polar bears are found.

Example 2.3: An argument that commits the fallacy of Hasty Conclusion
 
P1: All the polar bears we saw at the zoo today are white.
C: So, all polar bears are white.

Fallacy of Problematic Premise: An argument contains this fallacy if the premise set contains a premise that cannot be granted (accepted by the audience) without further support.

 

Notice that with example 2.4 the premise is relevant; it gives us some reason to believe the conclusion. Indeed, if the premise is true, it provides all the reason we need to believe the conclusion. To see the problem with this argument, imagine a friend of yours made this argument to you. Would you believe the premise? You probably wouldn’t without further evidence. You might ask your friend to convince you that she had not mistaken brown bears for polar bears. Perhaps your friend might convince you that this did not happen, but still this means that P1 requires more evidence for it to be acceptable. As it stands, it is an unacceptable premise.

Example 2.4: An argument that commits the fallacy of Problematic Premise
 
P1: All the polar bears we saw at the zoo today were brown and small.
C: Not all polar bears are white.




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