Thinkin’ about Logic

Using the Toulmin system to evaluate arguments

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.

What are we assuming?

We should buy the car that is most economical.

Economy is the major factor we should consider.

We should buy the car that is safest.

Safety is the major factor we should use in choosing a car.

We should buy this Ford Falcon because it is red.

Being red is the most important factor in selecting a car.

How can we support or refute the assumptions?

•I agree that we should buy the most economical car, but the Geo Metro isn’t 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 don’t 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.

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)?

So…wanna buy the red Falcon?

Why not? Don’t you believe it’s red?

100% of people surveyed say it’s red.

Chemical spectroscopy test verifies the color red.

Oh…what does color have to do with buying a car?

Oh…so you can’t 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.

Toulmin’s 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)

Toulmin’s 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

Toulmin identifies the three essential parts of any argument as the claim, the data (evidence which supports the claim) and the warrant.

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.

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

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.

Q: When might we need backing (support for the warrant) and not grounds (support for the data)?

Remember the ultra-safe Volvo?

A: When the writer and audience agree that the Volvo is the safest car, but disagree on whether safety is the most important factor.

Ah, but what about the Falcon, the car we should choose because it’s red?

Claim: We should buy the Ford Falcon.

Data: It is red.

Grounds: Everyone agrees it’s red; scientific analysis confirms it.

Warrant: We need a red car.

Backing: ???? (Can you think of a reason?)

How will this kind of analysis help me understand other people’s arguments?

How will this kind of analysis help me formulate my own effective arguments?