Thinkin

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Thinkin about Logic

• Using the Toulmin system to evaluate arguments

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What car should we buy?
We should buy this Geo Metro because it is
extremely economical.
We should buy this used Volvo because it is very
safe.
We should buy this Ford Falcon because it is red.
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What are we assuming?
We should buy the car that is most
economical. Economy is the major factor we should
consider.
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We should buy the car that is safest. Safety is
the major factor we should use in choosing a car.
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We should buy this Ford Falcon because it is
red. Being red is the most important factor in
selecting a car.
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How can we support or refute the assumptions?

• I agree that we should buy the most economical
  car, but the Geo Metro isnt it. The Mazda 3 is
  a better buy.
• I agree that we should buy the safest car. But a
  Humvee is safer than a Volvo.
• I dont agree with either criterion. These days,
  we should pick the car that gets the best gas
  mileage.
• I have 7 kids and a dog. I need the car with the
  most passenger and cargo space.

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Are we attacking the stated reason itself (We
should buy the Metro because it is most
economical) or the assumption behind it (We
should choose the most economical car)?
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Sowanna buy the red Falcon?
Why not? Dont you believe its red?
100 of people surveyed say its red. Chemical
spectroscopy test verifies the color red.
Ohwhat does color have to do with buying a car?
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Ohso you cant see how we got from the fact (the
car is red) to the claim (we should buy it).
What we need is some kind of argument to back up
this unstated assumption that redness is the
major criterion we should choose.
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Toulmins Analysis

• Stephen Toulmin, a modern rhetorician, believed
  that few arguments actually follow the classical
  models of logic like the syllogism.
• Review Example of syllogism
• All men are mortal (premise)
• Aristotle is a man (premise)
• Therefore, Aristotle is mortal (conclusion)

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Toulmins system

• Model for analyzing the type of argument you
  encounter in everyday life
• Identifies the basic parts of an argument
• You can use it two ways
• To identify and analyze the sources you use for
  information
• To test your own argument

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Toulmin identifies the three essential parts of
any argument as the claim, the data (evidence
which supports the claim) and the warrant.
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For example
Claim We should buy this used Volvo. Data
(stated reason) It is very safe. Warrant
(unstated assumption) We should buy the car
that is the safest.
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For example
Claim We should buy this used Volvo. Data
(stated reason) It is very safe. Grounds
facts, examples, evidence to support data Warrant
(unstated assumption) We should buy the car
that is the safest. Backing facts, examples,
evidence to support warrant
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Back to the Geo Metro that we should choose
because it is the most economical
Q When might you need grounds (support for the
data) but not backing (support for the warrant)?
A Writer and audience agree that economy is the
most important factor they disagree on which car
is most economical.
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Remember the ultra-safe Volvo?
Q When might we need backing (support for the
warrant) and not grounds (support for the data)?
A When the writer and audience agree that the
Volvo is the safest car, but disagree on whether
safety is the most important factor.
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Ah, but what about the Falcon, the car we should
choose because its red?
Claim We should buy the Ford Falcon. Data It
is red. Grounds Everyone agrees its red
scientific analysis confirms it. Warrant We
need a red car. Backing ???? (Can you think of
a reason?)
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How will this kind of analysis help me understand
other peoples arguments? How will this kind of
analysis help me formulate my own effective
arguments?