In most research and class-assigned papers the aim of the writer is to take a topic and assert an opinion about it. This assertion is better known as the writer's argument. With it the writer tries to win the reader over to his or her point of view about the topic, or, at the very least, to force the reader to see the subject discussed from an innovative perspective. If the writer is going to make some headway with an argument, however, he or she must be able to give evidence to support the claims that the paper will make. There are three main categories of evidence that are essential to gain the audience's basic confidence in the writer's assertions. These categories are facts, judgments, and testimony.

Facts

Facts are probably the best tools to get the reader involved in the argument. Since facts are indisputable, the writer automatically wins the mutual agreement of the reader by utilizing them. A statement such as this, "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 mostly to get the reader to stand on the writer's plane of reasoning. For instance, were the writer to argue that smoking cigarettes is detrimental to your health, he or she would begin by citing factual information about the large numbers 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.

Judgments

Facts, however, cannot carry the entire argument. It is necessary for the writer to use judgments as well. These are assumptions that the writer makes about his or her subject after carefully considering the facts. For example, a writer presents certain facts about the knowledge that scientists had about the condition of the Space Shuttle Challenger before its takeoff. From these facts the writer concludes that the disaster could have been avoided had only a few scientists been willing to protest. 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. This is where human reasoning comes in. 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.

Testimony

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 who saw an event happen, 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 the opinion of a astrophysicist about the condition of the Shuttle before takeoff and whether or not it was obvious from the evidence that the Shuttle should not have been launched.

However, the writer must use some caution when employing these two types of testimony in his or her paper. Eyewitness accounts cannot always be reliable; sometimes people do not always have the facts straight since everyone has a subjective view when witnessing events. Expert opinions are not beyond dispute; another expert in the same field of study may find faulty reasoning in the judgment of the first expert. Also, the writer must be careful not to use an expert in one field to make a judgment about a subject in another. For example, imagine the computer genius Bill Gates making a statement on toothpaste.