Why does a writer believe the claim s/he makes? The reasons a writer gives are the first line of development of any argument. To use our "house of cards" image again, reasons comprise the second level of an argument, without which the uppermost level (the claim) cannot remain balanced (or, in the language of argument, "effective").
How can we tell if reasons are strong? In other words, how can we determine whether or not they are sturdy enough to support the claim? Using the Toulmin method, we ask two main questions: Is the reason relevant to the claim it supports? and Is the reason effective?
Determining the Relevance of the Reasons
In order to evaluate the effectiveness of reasons used in an argument, we must first determine whether or not they are relevant to the claim they mean to support.
Determining the Effectiveness of the Reasons
If a reason is effective (or "good"), it invokes a value we can believe in and agree with. Value judgments, because they are by necessity somewhat subjective, are often the most difficult to make in arguments. It is, therefore, always a good idea to restate the value being invoked as clearly as possible in your own terms. Then you'll be able to evaluate whether or not the value is good in itself or worth pursuing.
If an argument's claim is
Argumentation is an important skill to learn,
No other type of writing requires a great deal of thought.
is arguably not very effective, since many people would not agree with or value this idea. (Notice, too, how qualification might help this reason.) On the other hand, a reason like
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
would be likely to give the impression of being effective (and supportable).