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One of the reasons that theories are a persuasive category of evidence is that they offer apparently rational explanations for the relationships between and among facts. Contrary to popular opinion, facts do not speak for themselves. In the example presented above, someone might have noticed an increase in pedestrian deaths following the introduction of seatbelt laws, but might not be able to explain why the two phenomena were related. The theory provides just such an explanation. Furthermore, that explanation can then be generalized to other arenas that involve risk. So, a debater might use the theory to argue about related phenomena, such as sports helmets and speed limits.
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Theories are important as evidence because they go beyond “mere” facts and provide seemingly sensible interpretations of the importance and meaning of the facts. Even explanations that are not formal theories are frequently necessary complements to factual evidence.
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16.1.1.3 Presumptions Presumptions are a kind of evidence that does not necessarily describe reality, but describes how people expect reality to be. As such, presumptions are based on what people expect to happen in the ordinary course of events. Presumptions are based on facts, even though they are not facts themselves.
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Presumptions can include assumptions about the nature of people in general, or about specific persons. They also can be about events expected to occur or not occur. For instance, we presume that, next winter, the weather in Guangxi will be warmer than the weather in Harbin. That presumption is not an observable fact because we cannot observe next winter’s weather today. However, the weather in Guangxi has been warmer for so many winters that we presume it will, again, be warmer next winter. We can use that presumption as evidence for a number of arguments, such as, where the family might vacation next December.
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Sometimes, we make presumptions about a particular person based on our previous knowledge of that person or that person’s family characteristics. For instance, someone might argue that Wang Jingkai will become a public servant in China because many of his family members have done so. In this case, the presumption that a particular person will go into public service is based on a fact that other members of his family did just that.
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The laws of many nations contain a concept called a “rebuttable presumption.” Those presumptions are “rebuttable” because a legal system has declared that the presumption stands until other evidence overcomes it. In the area of adoption law, for example, a rebuttable presumption is used to presume that, if a woman is married when she gives birth to a child, her husband is the father. Thus, when one sees a child accompanied by a married woman and her husband, that person might presume that the wife is the mother and the husband is the father. Although one can think of numerous reasons why the presumption might be incorrect, it is a presumption, nevertheless.
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16.1.2 Evidence Based on Preference
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Because presumptions are frequently as much about how things “ought” to be as about how they really are, presumptions blur the distinction between evidence pertaining to reality and evidence pertaining to preference. The next three categories, however, provide examples of evidence that falls squarely in the category of evidence pertaining to preference.
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16.1.2.1 Value Values provide evaluations of objects, persons, ideas, institutions, etc. Any statement expressing something other than indifference about an object7 is a statement of value. By their nature, values are abstract, but can become more concrete when connected to an object to be evaluated. To argue that Ge is pretty or Jinkai is handsome is to attach a value of beauty to a human object. Although evidence is ordinarily thought of as factual, values also serve as evidence in argument.
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One clear example of how a debater can use value as evidence occurs in arguments about the American system of health care. America is currently involved in an argument over whether it should provide universal health care to all citizens. Those who favor universal health care believe that the right to health care is an important value. Therefore, the value of the right to health care might be used as evidence to support the claim American should adopt a system of universal medical care for all its citizens. Because we do not ordinarily think of values as evidence in argumentation, perhaps a diagram of such an argument may help explain that category:
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The example in the previous diagram shows how a value can be combined with a fact to provide evidence to support a claim. In that case, the value involves the right to health care, and the fact is a statistic involving the number of Americans who do not have access to health care. Both of the two pieces of evidence are then combined to support a claim that “America should adopt a system of universal health care.” This example demonstrates that values can be important sources of evidence, especially in claims of evaluation.
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One problem in using values as evidence is that sometimes audiences hold competing values related to a particular object. With regard to the previous illustration of universal health care, some might also maintain the value of the necessity of reducing the cost of government. While the right to health care might be used to argue for the claim that America should provide a system of universal health care, the value of reducing the cost of government might mitigate against that claim. In situations where values such as the right to health care and the cost of government collide, the more important type of evidence concerns value hierarchies.
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16.1.2.2 Value Hierarchies Value hierarchies order values and establish certain values as more important than others. Value hierarchies are important only when values collide. A person who could choose to act on both of two values would have no reason to order those two values hierarchically.
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So, for instance, if a debater were to use a value hierarchy to argue about the right to health care, he or she might start with a value hierarchy that places the right to health care higher than the cost of government. The reason that one of those values is placed hierarchically over the other is because the two values might interfere with one another—especially in the case of the right to health care and cost of government where people might not be able to achieve both values and thus would be forced to choose one over the other. Such an argument might be illustrated as follows:
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In the example above, the evidence consists of a value hierarchy that places the right to health care over the cost of government. The evidence is then linked to the claim that adopting a system of universal health care is worth the cost of increasing the cost of government. In a great number of debates, arguers find themselves faced with situations where their audiences favor two or more sets of values that seem to collide. In those situations, debaters must determine the proper hierarchy of values and use it as evidence for their positions.
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16.1.2.3 Value Categories Value hierarchies can be thought of as existing in different categories. Philosophers Perelman and Olbrechts-Tyteca sorted hierarchies into six categories: quantity, quality, order, existence, essence, and person (1969: 85-94). Some hierarchies simply are founded on the category of quantity. That category assumes that more is better than less, thus, more money is higher on the hierarchy than less money. On the other hand, a person whose value hierarchies are organized according to quality probably will argue for something based on its uniqueness or irreplaceability. Therefore, according to the category of quality, the unique or rare is valued more than the common and replaceable. The dispute about global climate change can be used to illustrate the category of quality. The category of quality could be used to assert the importance of the irreplaceable (the environment) over the replaceable (the economy). A debater might use evidence consisting of quality to support a claim that protecting the environment is more important than sustaining the economy. A damaged economy can be restored, but a damaged environment is much more difficult to repair. Thus, the values associated with the environment are unique and irreplaceable. An example of such an argument using evidence from this value category is illustrated below:
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Books about debating rarely treat the last three categories (values, value hierarchies, and value categories) as evidence. Nevertheless, they are important forms of evidence when debating propositions that require evaluation. In addition, because evaluation is central to argumentation and debate, those three categories are quite important.
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16.2 Citing and Documenting Evidence
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Before concluding this chapter about evidence, a few words about citing and documenting evidence are important. The claim, since the debater creates it, can be considered the creative work of the debater. On the other hand, evidence usually does not consist of material created by the debater, but rather of material that is found using some formal or informal method of research. Thus, evidence is usually supporting material that is external to the debater; it is discovered rather than created. For that reason, the debater has an obligation to inform opposing debaters, judges, and audiences where the evidence was discovered. If the evidence consists of personal observations, the debater is obliged to let others know about the nature of those personal observations. If, as is frequently the case, the evidence was discovered by reading and surveying relevant publications on the subject, the debater is obliged to inform others where the evidence was found. How much detail should the debater report when citing the evidence? A good rule of thumb is that the debater should be prepared to provide sufficient detail that would allow the listener (or reader) to find the evidence on their own. The debater should be prepared to offer the name(s) of the author, the title of the book, magazine, or document from which the evidence was extracted, the title of the article in the book or magazine, the date of the article, and the pages on which the information appeared.
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Most who listen to an oral argument do not expect to hear all of the citation for every piece of evidence, but they do expect that the debater would provide the complete citation if requested. So, a debater might say something like “According to a study conducted in 1975 by Professor Samuel Peltzman…” with the expectation that he or she would present the rest of the citation on request. In a written argument, the arguer needs to present the entire citation in the text. The difference between oral and written argument with regard to citing evidence is that a reader cannot always ask the arguer for a citation because the writer and reader may not be in the same physical location. On the other hand, speaker and listener are almost always physically together, so the need to present the entire citation orally is reduced. The important point about citing and documenting evidence is that the debater needs to present or at least be prepared to present enough information so that the listener can find the evidence using only the citation that the debater presents.