The Toulmin Method

The Evidence

We would all probably like to believe that the people we argue with will accept our claims and reasons as perfect and complete by themselves, but most readers are unlikely to do that. They want evidence of some sort--facts, examples, statistics, expert testimony, among others--to back up our reasons. If this level of the house of cards is either unstable or absent, neither of the two levels it supports (the reasons and claim) can be effective.

To be believable and convincing, evidence should satisfy three conditions. It should be sufficient, credible , and accurate.

Determining the Sufficiency of Evidence

As you look at the evidence supporting a reason, ask yourself if the author makes use of enough evidence to convince a reasonable reader.

If one reason given in an argument is

If you look at writing assignments given in various disciplines of the university, you will find that many of them include elements that are related in some way to argument.

An example from one Engineering assignment would most likely be insufficient, where several such examples would provide a more varied range of situations in which the stated reason holds true.

Determining the Credibility of Evidence

It is important to decide how credible (believable and authoritative) a piece of evidence is within an argument. As you look at the evidence supporting a reason, ask yourself whether or not this evidence matches with readers' experience of the world. If it doesn't, does the evidence come from a source that readers would accept as more knowledgeable or authoritative than they are?

If one reason given in an argument is

On the university level, argument is valued by professors of various disciplines who say that they would like for their students to be able to take a strong position and support it with ample reasons and evidence, statistics taken from The National Inquirer and given in support of this reason will typically be much less credible than ones taken from The Journal of Higher Education.

Determining the Accuracy of Evidence

As you look at the evidence supporting a reason, ask yourself if this evidence "tells the truth." Are statistics gathered in verifiable ways from good sources? Are the quotations complete and fair (not out of context)? Are the facts verifiable from other sources?

Sometimes it is difficult to determine accuracy without having the writer's sources in front of you, but there are oftentimes cases in which you will be suspicious of a piece of evidence for one reason or another.

If, in support of a reason like

College students are very enthusiastic about learning argumentation skills

a writer uses this piece of evidence:

In a survey conducted in my residence hall, 92% of the respondents asserted that they enjoyed writing arguments more than any other activity listed on the questionnaire,

you might be led to ask questions like "Who conducted this survey?" "Who were these respondents?" or "What were the other activities listed on the questionnaire?"

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