art courtesy of
Janet Preslar, FrActivity

Toulmin Logic

Toulmin Logic is a proof format that consists of three aspects:

  1. the claim, or conclusion
  2. the evidence for the claim, and
  3. the warrant, or unstated assumption
The basic idea is that every conclusion drawn should have both evidence, as well as shared, though unstated, assumptions that all of us share that help close the argument. Usually the claim or conclusion is stated first, followed by the evidence. The unstated warrant, then, should be easily identified by both writer and reader. For example, examine the following argument:

Claim: Parents should buy their kids Mattel toys.
a. Mattel makes high quality toys.
b. Mattel has competitive prices.
c. Millions of Mattel toys are bought by other parents every year.
Warrant: Parents should buy their kids toys of some kind.

The major aspects to consider with this particular logic mode is whether the evidence is valid on its face, whether it's valid for this particular instance, and whether it can support the claim without support other than what is offered in the proof. For instance, in whose opinion is this brand of toys "quality"? Was it an unbiased report (Consumer Reports) or the opinion of the company itself? Likewise, what does "competitive" pricing mean? Furthermore, do the purchases by other parents make this purchase a sound one? Could they be blindly buying an inferior product merely because of its popularity? Also, is the warrant truly a shared assumption or is this subject to individual opinion? Should parents be buying any toys at all, or is this an assumption that not all of us share? Much of this may be subjective, and thus the argument that ensues is not based on the validity of the claim as much as the validity of the warrant or the evidence. Often the claim is supported largely by preconceived assumptions that are really unproven assertions that the writer wants you to take for granted. Much of today's political discussion is based largely on preconceived beliefs by both Republicans and Democrats that make meaningful discussion near impossible. In other words, how do you change someone's belief system? When evaluating the validity of such claims, all these factors are important things to consider.

Several examples are given here. Evaluate the validity of all the factors to determine whether the argument is persuasive.

Republican Jones is a shoe-in to win the election.
Democrat Smith was convicted of fraud last week.
The other candidates are all Independents.
Only a Republican or Democrat can win an election.
A criminal conviction will sway votes.
The warrants of this argument have not proven absolutely consistent, even though logic does support this claim: first, a few candidates from other than the two major parties have won both state and national congressional posts. Likewise, Marion Barry, mayor of Washington DC, was reelected after being convicted and jailed for cocaine use.

You shouldn't break morality laws.
Some actions hurt other people.
All such actions are against God's will.
You will be punished by God when you die.
Hurting others is bad.
God exists.
Obviously, this argument hinges largely one's belief system. If the reader were to be an atheist or didn't care about other people, the argument is not convincing.

Stephen King writes quality fiction.
He sells millions of books a year.
His stories are made into movies.
There are books written about him and his work.
Popularity is indicative of quality.
In this example we have three bits of evidence all based on the warrant... and it is clear that popularity is NOT necessarily indicative of quality.

"PBS is free because it sucks" (Comedy Central radio ad, 7-27-98).
EVIDENCE (offered in ad):
PBS is information-based.
Comedy Central offers sexily clad women.
Comedy Central offers "adult" language and content.
WARRANT (not stated in ad but implied):
Culture is boring, or prurient content is exciting.
Culture is not worth paying for, or prurient interest is worth paying for.
Obviously, many would agree with this argument, since cable costs money and PBS is free. However, PBS is paid for by individual and corporate sponsorship (not advertisers nor cable subscription), so the warrant may not be supportable to a certain segment of the population.

It rained last night.
Car is wet
Street is wet.
Lawn is wet.
That much water in those places could only be due to rain.
Like the first example, the claim and warrant in this last example are based on likely outcome but overlook the possibility of the exceptions to these situations. Are there other possibilities to explain this situation? Errant sprinkler? Water truck? What is the likelihood of each? Based on probabilities, the claim in this last example is probably correct, but are there other possibilities?

Toulmin Logic is supposed to draw the user into a stricter logic process...and it can be used to evaluate claims by others. Be aware that it is difficult to get absolute "proof" of an argument, even when logic and past experience tell us the likely outcome (like examples 1 and 4). However, used correctly, this approach to argumentation can be effective.

© T. T. Eiland, January 1998
Last modified: March 30, 2000