Evidence is the information that supports a claim and persuades others to believe you. Just as a prosecuting attorney needs evidence to convince juries to convict a person accused of a crime—against the counterclaims of defense attorneys—you need evidence to convince audiences to believe you. Consider these four classes of evidence, each of which persuades in a different way:

1. Facts are things upon which everyone, regardless of personal experience or values, agrees. It is a fact that water boils at 212 degrees Fahrenheit at sea level, that Herman Melville published Moby-Dick in 1852, and that the college budget for new programs last year was $50,000. Facts are often, though not necessarily, numerical or statistical—things that can be measured and verified by standards we all accept.

2. Inferences are the generalizations or meaning we make from an accumulation of facts. Take, for example, the following three facts:

1. Phosphorous is a fertilizer.

2. Farmers use phosphorous to fertilize fields on the shores of Lake Champlain.

3. Studies of Lake Champlain indicate high phosphorous levels. Each fact taken alone means little; taken together, because each fact is related to the next, they support the inference that farms near Lake Champlain contribute to excessive algae growth in the lake.

3. Informed opinion is the viewpoint of experts in a particular field. Their testimony is good evidence because the rest of us trust their knowledge: We trust a lawyer to know more about the law, a doctor about medicine, a football coach about football, and a marine biologist about lake pollution. A good example of an informed opinion would be that of Professor Don Meals, of the College of Natural Resources, who recommends that the best way to reduce phosphorous contamination in Lake Champlain is to create a one-hundred-foot phosphorous-free buffer zone around the lake (1992).

4. Personal testimony is good evidence because it comes from a person with direct experience of an event or situation. The knowledge of the astronaut differs from the physicist's, the tenant's from the architect's, the fisherman's from the marine biologist's,the female's from the male's.Their testimony is experiential rather than expert, but has its own authority nevertheless.

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