Critical Thinking Skills and Logical Arguments

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Critical Thinking Skills and Logical Arguments
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Critical thinking

• Distinguish fact from opinion
• Argument process whereby a conclusion is drawn
  from a premise(s)
• Structure of logical argument
• Premise 1
• Premise 2 (optional)
• .
• .
• Premise n (optional)
• _________________
• Conclusion

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Chip X Example

• Premise 1 Observation of Chip X testing in Japan
• Premise 2 Possession of design specs
• Premise 3 Corroboration of eyewitness
• Conclusion Chip X is being developed

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Web site example

• Premise Writing a book on bomb-building is
  protected by the First Amendment
• Premise Building a web site is similar to
  writing a book
• Conclusion constructing a web site on
  bomb-building should be protected by the First
  Amendment

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Internet example

• Premise The internet is in public space
• Conclusion Personal privacy should not be
  expected on the internet

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Logical fallacies

• Ad hominem Attacks the person making argument
  rather than the argument itself
• Slippery slope A hypothetical possible negative
  outcome is assumed to come about
• Appeal to authority An expert endorses the
  argument
• False cause Assumes an outcome subsequent to an
  event was caused by the event
• Begging the question Assuming the conclusion

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Logical fallacies (continued)

• Fallacy of composition/division Assuming the
  whole/part has characteristics of the part/whole
• Fallacy of ambiguity Ambiguity in premises
• Appeal to the people If most people think its
  right then it is
• Many/any fallacy If property P exists in many
  instances of type T, then it exists in any
  instance of type T
• Virtuality fallacy (Moor) Cyberspace is virtual
  so no real harm can come from there

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Valid and invalid arguments

• Claims (premises) are true or false while
  arguments are valid or invalid
• Validity means that the conclusion necessarily
  follows from the premise(s) assuming the truth of
  the premise(s)
• The actual truth or falsity of the premises
  determines whether an argument is sound or
  unsound
• Strength of reasoning valid or invalid
• Actual truth of premises sound or unsound

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Figure 3-1
Arguments
Valid
Invalid

The assumed truth of the premises is sufficient
to guarantee the conclusion.
Premises (even when true) do not guarantee the
conclusion.
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Seven-step Strategy for Evaluating Arguments I
(Part 1 Steps 1-4)
Step 1. Convert the argument into standard form.
(List the premises first, followed by the
conclusion.)
Step 2. Test the argument for its reasoning
strength to see whether it is valid or invalid.
(Assume the premises to be true, and ask
yourself whether the conclusion must also be true
when those premises are assumed true. Is a
counterexample to the argument possible?)
Step 3. Is the argument valid? If yes, go to
Step 4. If no, go to Step 5.
Step 4. Is the (valid) argument also sound? That
is, are the premises true in the actual
world? 4a. If the argument is valid and if all
of the premises are true in the actual world,
then the argument is also sound. (To determine
truth-values for statements, see Appendix
E.) 4b. If the argument is valid, but one or
more premises can be shown to be either false or
not capable of being verified in the actual
world, then argument is unsound.
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Figure 3-2
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Inductive arguments

• Deductive argument premises provide certainty of
  conclusion
• Inductive argument premises provide likelihood
  of conclusion
• Even though invalid arguments cant be sound, if
  theyre inductive they can still be strong
• If the premises of an invalid argument dont make
  the conclusion sufficiently likely, the argument
  is fallacious

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Figure 3-3
Invalid Arguments
Inductive
Fallacious
Conclusion likely follows from assuming the truth
of the premises.
Conclusion does not likely follow from
assuming the truth of the premises.
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Figure 3-4 Comprehensive View of Arguments
Arguments
Valid
Invalid
Unsound
Sound
Inductive
Fallacious
Strong Arguments
Weak Arguments
Weak Arguments
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Seven-step Strategy for Evaluating Arguments I
(Part 1 Steps 1-4)
Step 1. Convert the argument into standard form.
(List the premises first, followed by the
conclusion.)
Step 2. Test the argument for its reasoning
strength to see whether it is valid or invalid.
(Assume the premises to be true, and ask
yourself whether the conclusion must also be true
when those premises are assumed true. Is a
counterexample to the argument possible?)
Step 3. Is the argument valid? If yes, go to
Step 4. If no, go to Step 5.
Step 4. Is the (valid) argument also sound? That
is, are the premises true in the actual
world? 4a. If the argument is valid and if all
of the premises are true in the actual world,
then the argument is also sound. (To determine
truth-values for statements, see Appendix
E.) 4b. If the argument is valid, but one or
more premises can be shown to be either false or
not capable of being verified in the actual
world, then argument is unsound.
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Seven-Step Strategy For Evaluating Arguments II
(Part II See Steps 1-4 on previous slide)
Step 5. Is the (invalid) argument inductive or
fallacious? (How likely will the conclusion be
true when the premises are assumed true?) 5a.
If the conclusion would likely be true because
the premises are assumed true, the argument is
inductive. 5b. If the conclusion would not
likely be true even when the premises are assumed
true, the argument is fallacious. (Keep in mind
that a fallacious argument can be made up of
Individual claims that are themselves true in
the actual world.)
Step 6. Determine whether the premises in your
argument are either true or false.
Step 7 Make an overall assessment of the
argument. That is, describe the argument's
strength of reasoning in conjunction with the
truth conditions of the argument's premises. For
example, is the argument inductive with all true
premises? Is it inductive with some false
premises? Is it fallacious with a mixture of true
and false premises, and so forth? Remember that
an inductive argument with premises that are all
true is stronger than a valid argument with one
or more false premises.)