The Argument: Types of Evidence


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

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.


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


Identify each of the following passages as Fact, Judgment, Eyewitness Testimony, or Expert Testimony.

1. "At the time I didn't know that Harvey was epileptic. His seizure came as a complete shock to me, as it did to the other guests at the house. When he fell on the ground, frothing at the mouth, we kind of panicked, I guess. We should have immediately called 911 and have gotten the medics over here right away, but instead we tried to handle the problem on our own. Larry got behind his head and tried to hold it steady, since it was violently thrashing from side to side. I, meanwhile, got close to Harvey's legs in order to stop them from kicking all around. Little did we know that our efforts would not only make matters worse, they would also lead to Harvey's untimely death."

David Stemple, personal interview, 12 March 1947.


2. "Harold McConnel, who has been working with and designing railroad tracks for the past three decades, after examining the scene of the accident at Geneva train station, came to the conclusion that someone had tampered with the track and had bent it out of shape. This, in turn, led to the collision of the two passenger trains on Wednesday."

Staton, Greg H. "Tragedy at the Train Station." Chicago Tribune, 22 April 1989: A5.


3. "Howard's Department Stores declared bankruptcy yesterday after assessing the loss they made last year. The company had just opened five new outlets in the San Diego area, when it learned that its customer turnout in the Los Angeles and San Francisco area dropped to a record low. In its vain attempt to support the new outlets in the south while increasing its advertisement in the north, the company floundered."

Hodges, Carol S. "Ho-boy, Howard!" Los Angeles Times, 4 July 1973: B7.


4. "I think that from the evidence presented to us—the results of the doctor's tests, the testimony of people who have used the drug, and the opinion of expert pharmacists—we can carefully conclude that the affects of marijuana smoking are much more negative than positive. This will come as a shock to thousands of groups who hold to the contrary."

James, Fred T. "The Myth About Marijuana." Time Magazine, 12 October 1976: 53. 


5. "The scene was entirely out of control. I was standing only ten feet away from the President, who was walking through the crowds on the sidewalk of Jefferson Ave., when the incident occurred. Before I knew what was happening, a tall man, wearing a ski mask and a dark leather jacket, ran up beside the President, took out what seemed to be an Uzi, and fired three rounds into his skull. Immediately all hell broke loose; people were scurrying everywhere, looking for shelter. The President's bodyguards took off after the assassin, and, since he would not stop at their orders, killed him as well."

Broberg, Greg. Interview with Tom Yarrow, head of the FBI. New York Times, 14 March 2005: A2.

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