The Argument: Types of Evidence

Argumentation and Evidence

In most papers, the writer’s aim is to find a topic and make a claim about it. This claim is better known as the writer's argument. 

With it, the writer attempts to win the reader over to his/her view of the topic, or, at the very least, to show the reader a new perspective about the subject discussed. If the writer is going to make some headway with an argument, however, he/she must be able to give evidence to support the claims the paper will make. There are three main categories of evidence that are essential to gain the audience's confidence in the writer's assertions. These categories are Fact, Judgment, and Testimony.

This page explores the types of evidence used in argumentation. See also the page on logic and argumentation.


Facts are among the best tools to involve the reader in the argument. Since facts are indisputable, the writer automatically wins the reader’s mutual agreement by utilizing them. A statement declaring, "On January 28, 1986, the shuttle Challenger exploded upon lift-off," must be accepted by the reader, since it is a historical certainty. Facts are used primarily to get the reader to stand on the writer's plane of reasoning. For instance, if a writer wanted to argue that smoking is a detriment to your health, he/she would begin by citing factual information about the large number of people who die every year from smoke-related diseases. This would then force the reader to agree with the writer on at least one point.


Facts, however, cannot carry the entire argument. It is necessary for the writer to utilize Judgments as well. These are assumptions that the writer makes about his/her subject after carefully considering the facts. For example, a writer could start by presenting certain facts about the knowledge that scientists had regarding the condition of the Challenger prior to takeoff. From these facts, the writer concludes that the disaster could have been avoided if a few scientists been willing to speak up about some unsettling findings. This would be a judgment on the writer's part. There is nothing in the history books or newspapers that can prove this assumption to be true. The success or failure of the entire argument rests on whether or not the writer can utilize adequate reasoning in coming to the right judgments.


The final type of evidence used in writing a convincing argument is Testimony. There are two types of testimony: 1) the account of an eyewitness, and 2) the judgment of an expert who has had the chance to examine and interpret the facts. Both of these lend validity to an argument. The eyewitness can supply important facts for the writer to use, and the expert can provide valuable judgments in order to give strength to the argument. For instance, in the case of the Space Shuttle Challenger, the writer might use the testimony of one of the personnel who was present at NASA meetings before the launch. The writer might also use an astrophysicist’s opinion about whether or not evidence existed before takeoff that the Shuttle was not safe to launch. 

However, the writer must exercise caution when employing these two types of testimony in his or her paper. Eyewitness accounts cannot always be reliable; no one person has an objective view of an event. Also, an expert’s opinion is not beyond dispute; another expert in the same field of study may find faulty reasoning in the first expert’s judgment. Also, the writer must be careful not to use an expert in one field to make a judgment about a subject in another. Imagine the absurdity of computer genius Bill Gates making an official statement on archeology.


Internet Resources 

>> Dartmouth Logic and Argumentation Guide


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