Stephen Toulmin, originally a British logician, is now a professor at USC. He became frustrated with the inability of formal logic to explain everyday arguments, which prompted him to develop his own model of practical reasoning.

The first triad of his model consists of three basic elements:

A claim is the point an arguer is trying to make. The claim is the proposition or assertion an arguer wants another to accept.

The claim answers the question, "So what is your point?"

example: "You should send a birthday card to Mimi, because she sent you one on your birthday."

example: "I drove last time, so this time it is your turn to drive."

There are three basic types of claims:

fact: claims which focus on empirically verifiable phenomena

judgment/value: claims involving opinions, attitudes, and subjective evaluations of things

policy: claims advocating courses of action that should be undertaken

Grounds refers to the proof or evidence an arguer offers.   Grounds answers the questions, "What is your proof?" or "How come?" or "Why?"

Grounds can consist of statistics, quotations, reports, findings, physical evidence, or various forms of reasoning.

example: "It looks like rain. The barometer is falling."

example: "The other Howard Johnson's restaurants I've been in had clean restrooms, so I'll bet this one has clean restrooms too."

grounds can be based on:

evidence: facts, statistics, reports, or physical proof,

source credibility: authorities, experts, celebrity endorsers, a close friend, or someone's say-so

analysis and reasoning: reasons may be offered as proof

The warrant is the inferential leap that connects the claim with the grounds.

The warrant is typically implicit (unstated) and requires the listener to recognize the underlying reasoning that makes sense of the claim in light of the grounds.

The warrant performs a "linking" function by establishing a mental connection between the grounds and the claim

example: "Muffin is running a temperature. I'll bet she has an infection." warrant: sign reasoning; a fever is a reliable sign of an infection

example: "That dog is probably friendly. It is a Golden Retriever." warrant: generalization; most or all Golden Retrievers are friendly

warrants can be based on:

ethos: source credibility, authority

logos: reason-giving, induction, deduction

pathos: emotional or motivational appeals

shared values: free speech, right to know, fairness, etc.

note: these categories aren't mutually exclusive, there is considerable overlap among the three

The second triad of the Toulmin model involves three addditional elements:

Backing provides additional justification for the warrant.

Backing usually consists of evidence to support the type of reasoning employed by the warrant.

The qualifier states the degree of force or probability to be attached to the claim.

The qualifier states how sure the arguer is about his/her claim

The rebuttal acknowledges exceptions or limitations to the argument.

The rebuttal admits to those circumstances or situations where the argument would not hold.