La interculturalidad y el profesorado

CONCLUSION: It is implausible that I would attack him.

This argument matches the plausible argument of the weaker man, above. Thus the one plausible argument functions as a rebuttal of the other. This argument works pretty much the same way. The jury would find it plau- sible because they can mentally put themselves individually into the sit- uation of the arguer. A person on the jury would be aware that the larger man would be putting himself in a bad position by assaulting the smaller man, and so they can easily see why the larger man would be reluctant to do so. By using this plausible counter-argument, the stronger man was able to cancel out the shift in the burden of proof that made him appear to be guilty.

7. Plausible Argumentation 71

Plausibility is different from probability. Probability is determined by collecting data on the statistical chances of what happened, and then using that data to judge how likely a statement is to be true. Plausibility is a matter of whether a statement appears to be true in a normal type of situation that is familiar both to the participants and the onlookers. In the example of the smaller man’s argument above, the onlookers can be expected to see that if he were to start such a fight, he would realize that the consequence would be a humiliating defeat. Judging by appearances and by what would normally happen in a situation the onlookers are familiar with, they conclude it is implausible that the smaller man would start the fight. Of course, this conclusion is based on other things being equal. Suppose it was shown by evidence in the trail that the smaller man was a skilled boxer and was generally aggressive. And suppose that further evidence was introduced showing that the larger man was clumsy and was not an aggressive person. These additional facts would mean that the conclusion drawn in the case might be quite different.

Another classic example of reasoning based on plausibility is the case of the snake and the rope.6_{A man sees a coil of rope in a dimly lit room. It}

looks like a snake, and not wanting to get bitten, he acts on the plausible assumption that it is a snake by jumping over it. When he turns back, however, he sees it did not move. He now reasons that it is not very plausible that it is a snake and that it is plausible that it is a rope. But, then again, he thinks, snakes are sometime motionless. So he carries out a test. He prods the object with a stick. It still fails to move, and he concludes that the object is a rope. In this case, initial appearances suggested that the object might be a snake or a rope. The man could not be sure. But since there was a danger of snakebite, he acted on the plausible assumption that it was a snake. He took care to jump over it. But then new information entered the case. He saw that the object failed to move when he jumped over it. This evidence indicated that it was probably not a snake. To get even more evidence, he carried out a test by prodding the object. The test confirmed the hypothesis that the object was a rope and not a snake.

Still another example shows how a statement that is implausible might turn out to be true. John Locke, an eighteenth-century philosopher, presented the example of the Dutch ambassador who was entertaining the king of Siam to illustrate plausibility.7_{The ambassador told the king}

6_{This example, attributed to the Greek philosopher Carneades, can be found in a book by}

the skeptical philosopher Sextus Empiricus, Against the Logicians, 188.

7_{John Locke, An Essay on Human Understanding, 9th ed. (London: A. Churchill, 1726),}

that water in the Netherlands would sometimes, in cold weather, be so hard that men could walk on it. He said that this water would even be so firm that an elephant could walk on the surface. The king found this story so strange that he concluded the ambassador had to be lying. The story makes the point that plausibility refers to an inference drawn on the basis of normal, commonplace expectations based on conditions that a person is familiar with. In the tropics, people were not familiar with freezing conditions, and hence the story of the freezing canal did not fit in with the normal expectations they had in their environment. They just found the ambassador’s statements implausible and unconvincing.

Still another example of plausibility is a statement accepted on the basis of an appeal to expert opinion. If an expert asserts a statement as true, that is a plausible reason for thinking that the statement is true. It could turn out that this statement is not true. The expert could be lying or could just be wrong. But still, other things being equal, if a person is not an expert himself and lacks much knowledge about the subject in question, it could be wise to accept the opinion of an expert as plausible. It could be a plausible assumption to act on, as long as one is open to new evidence that might come in.

Inductive arguments are based on probability, in the statistical mean- ing of this term. Plausible arguments are based on presumption. A pre- sumption is a qualified, tentative assumption of a proposition as true that can be justified on a practical basis, provided there is no sufficient evi- dence to show that the proposition is false. In computer science, this way of drawing an inference is called ‘defeasibility’. Plausible inference is based on a generalization or a conditional premise that is of the defeasi- ble type, where there are qualifications that need to be made and where it is not known whether these qualifications apply to the given case or not. Until such knowledge comes in, a tentative conclusion can be inferred by defeat. The classic case used in computer science to illustrate default is the Tweety example.

THE TWEETY EXAMPLE