There is a tendency for debaters and judges to view a single quote or opinion as conclusive evidence proving a point. But evidence can only point toward a conclusion; it cannot prove a conclusion conclusively. Experts may offer their opinions (sometimes as fact) but these opinions are only educated guesses. This is not to say that evidence from authorities has no use in debate, but that the degree of certainty attributed to an argument which is supported solely by an individual quotation is quite low. Because reasons are what give an argument validity, debate trainers should require that debaters understand the reasons for the expert's conclusions rather than just accept the expert's conclusions uncritically. Judges often contribute to another faulty view of evidence, by placing high standards on the content of an evidence card and by allowing the debaters no option to draw inferences not clearly indicated in the evidence. This view is misguided, in that, again, evidence can only suggest the probability of an action--not guarantee it. In debate, teams supporting a conclusion should state their conclusion, and then indicate the data that support that conclusion. They need not prove that the theory is 100% certain. The judge should then evaluate on the probability that the conclusion is true. The usefulness of evidence in debate depends on the type of conclusions that a debater attempts to support: fact and prediction, where "qualifications" of expertise best enhance probability; claims of value, where expert opinion has little weight; and argument over debate theory, in which quotations from experts are also of little use. (HTH)