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6.4: Using Evidence

  • Page ID
    67180
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    In his book, ARGUMENTATION AND DEBATE, Austin J. Freeley discusses the uses of evidence. He says that the various types of evidence can be used in two ways:

    To establish Conclusive Proof for your position. Conclusive proof is using evidence that is strong and convincing enough to override any objections to it. This evidence is so strong that the law will not permit it to be contradicted.

    Often the argumentative environment will define what type of evidence is needed to establish your arguments to the defined threshold of that environment. For example, fingerprints at the crime scene may be the conclusive proof needed to find a person guilty of that crime. For a scientist to prove a hypothesis they need an experiment to reach a 95% certainty threshold. That is, they need to be 95% certain of the results. If the experiment by the scientist reaches this level, this would be conclusive proof.

    To establish Circumstantial Proof for your position. This is where the various types of evidence are used to form a link strong enough to prove your point. Using the different types of evidence as support gives the argument the strength needed to establish the accuracy of your argument. The evidence is put together in such a manner so as to create an evidence chain. One bit of evidence is connected to another, and so on. Each piece of evidence, in and of itself, is not enough to reach the threshold of your audience for accepting your argument, but taken altogether, the accuracy of the claim can be established. 1

    Many Americans hold the incorrect view that circumstantial evidence cannot be used to convict someone in a court of law. In fact, more convictions are based on circumstantial proof than on conclusive proof.

    How Much Evidence is Necessary?

    All good arguments must be supported by a strong foundation of evidence. An argument filled with no supporting evidence is merely an assertion. It is instead a collection of interpretations or beliefs, and the audience will have no reason to believe the interpretations or beliefs if they are not well supported with evidence.

    How much evidence do you need to support each contention that you make in support of your stand on a claim? Good question. To some extent, the amount of evidence needed depends on the degree of controversy of the claim you are trying to support and your credibility as an advocate. Thus, how much evidence an advocate needs to present is ultimately determined by the demands of his or her target audience. Since evidence must ultimately be persuasive to an audience, arguers must adjust their usage of evidence for maximum appeal. An advocate must deal with one of the following audience types:

    A friendly audience is one that already supports an advocate’s position on a claim. Audience members are already predisposed to granting adherence to the position, so very little additional evidence is needed as support.

    A neutral audience is one that has made no commitment to granting adherence to the advocated point of view. Audience members are “fence sitting,” waiting to see what type of support can be provided in order to move them over to one side or the other. The quality of the evidence used is important to this type of audience.

    A hostile audience is one that is opposed to the advocate’s point of view. Audience members are already predisposed to reject the advocated point of view. In this case, a great deal of high-quality evidence is needed in order to move audience members off their existing position.

    Tests of Evidence

    You have evidence that you plan to use in your arguments. The key question for you, because it will be a key question for your audience, is whether the evidence is accurate, whether you can trust it. Unless you are reporting your own personal experience directly to us, your evidence comes from somebody else.

    If you use the word of some other person or group to answer the question “How do you know?” it just moves the question back a step: How do they know? Even if you understand them, and they were correct as they saw it, they may have been just plain wrong. If you really care about the accuracy or correctness of what you are reporting, then you have to have some way of checking the reliability of your sources. In reviewing evidence, you can use a few tests that are widely used to evaluate evidence.

    Recency: Is the evidence too old to be of current relevance to the issue? Would the source have had knowledge of recent developments or discoveries that might have bearing on the issue?

    Sufficiency: Is there enough evidence to justify all of the claims being made from it?

    Logical Relevance: Does the claim made in the evidence provide a premise which logically justifies the conclusion offered? Can you reasonably draw the conclusion being urged based on what the evidence says?

    Internal Consistency: Does this source make claims that are contradicted by other claims from the same source?

    External Consistency: Are the claims made by this source consistent with general knowledge and other evidence? If not, does the writer account for this discrepancy? If printed, can it be found? If not in print format, can you provide citation as to time, place and date?

    Reference

    1. Freeley, Austin J. Argumentation and Debate. Wadsworth Publishing Co., 1993

    This page titled 6.4: Using Evidence is shared under a CC BY-NC 4.0 license and was authored, remixed, and/or curated by Jim Marteney (ASCCC Open Educational Resources Initiative (OERI)) .

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