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That study gathered statistics about two variables: hukou reform, and the urban and rural income gap. The statistics were gathered systematically about each of the two variables and then were interpreted in a way that allows the researcher (and consumers of the research) to make a further statement about the relationship of the two variables. Well-conducted empirical studies are persuasive because of the systematic way evidence is gathered and interpreted. In the previous example, the authors began with an underlying theoretical position that hukou reforms would decrease the income gap. The authors then systematically gathered evidence related to both variables and finally interpreted the statistical evidence as inconsistent with the theoretical position with which the study began. In this particular case, the statistician began with theoretical position, and the data gathered actually cast doubt on the original position. Like statistics, different people can interpret empirical studies in different ways. Debaters need to take care to cautiously and accurately interpret empirical studies.
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Thus, observed data, examples and illustrations, historical descriptions, statistics, and descriptions of empirical studies are included in the category called “facts.” Factual evidence of this kind, used well, can be quite persuasive in debate. Sometimes, a collection of facts is gathered together into a complex but coherent interpretation—a theory. The next category of evidence examines that idea of theory.
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16.1.1.2 Theories Theories are used to explain or predict and, thus, can be used as evidence in various cases. In scientific circles, theories are more important than “mere” facts. These theories are formalized statements seeking to predict physical and social phenomena with greater or lesser precision depending on the theory. For instance, formal theories like Albert Einstein’s general and specific theories of relativity or Charles Darwin’s theory of evolution make predictions and explain phenomena.
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But theories need not be that formal to be useful as evidence in argumentation and debate. For instance, debaters might use Samuel Peltzman’s theory of risk compensation to argue against the introduction of kinds of safety devices on automobiles. Peltzman’s theory, which grew out of a study in the mid-1970s about automobile regulation, has since become a much more general theory about risk compensation (Peltzman 1975: 677-726). In simple form, his theory asserts that, when governments issue safety regulations on things from automobiles to motorcycles to birth control devices, people who use those items engage in more risky behavior due to their perception that the safety concerns have been resolved.
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Thus, the Peltzman theory could be used as evidence to argue against instituting more stringent seatbelt laws in China. The argument might go like this: Seatbelt laws will make drivers feel safer; that feeling of safety will cause drivers to drive more recklessly, thus endangering pedestrians and cyclists. The following diagram provides a visual illustration of such an argument:
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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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思辨精英：英语辩论-构筑全球视角 [:1705132481]
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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.