1.                    You have four patients who are quite seriously ill. You suspect that it is because last night they ate spaghetti contaminated with bacterium X and that that caused an infection with bac. X. Time is pressing: you want to know as quickly as possible whether the spaghetti was the source of bac. X.

This is what you already know:

                                      | Bob        Carol        Ted        Alice

-----------------------------|--------------------------------------------

Ate spaghetti              | Yes        No                ?            ?

Has bac. X infection   |   ?            ?                 Yes       No

You can test for a bac. H infection, and you can test for having eaten spaghetti. What tests do you run for the quickest possible test of your hypothesis?

2.                    (Cederblom/Paulsen Critical Reasoning, ex. 9.4)

The passage that follows contains a theory.

a.                   List the most important aspects of the theory as well as any significant regularities or patterns explained or predicted by the theory.

b.                   Sketch criticisms of the theory using the techniques for the Criticism of Theories in the last lecture.

c.                   Assess some of the arguments in the passage.

                  Benefit of Handguns

What evidence is there that handguns in private hands protect the lives and property of innocent persons? First of all, there is the burglary data. The chart below sets forth crime and suicide rates for several nations, per 100,000 population.

While the U.S. has much more violent crime than the other nations (including crimes such as rape, which rarely involve guns,) the U.S. anomalously has less burglary. In terms of burglaries perpetrated against occupied residences, the American advantage is even greater. In Canada, for example, a Toronto study found that 48% of burglarie were against occupied homes. Similarly, most Canadian residential burglaries occur in the nighttime, while American burglars are known to prefer daytime entry to reduce the risk of an armed confrontation. After Canada’s stricter 1977 controls (which generally prohibited handgun possession for protection) took effect, the Canadian overall breaking and entering rate rose 25%, and surpassed the American rate, which had been declining. A 1982 British survey found 59% of attempted burglaries involved an occupied home (again compared to just 13% in the U.S.)

Why should American criminals, who have proven that they engage in murder, rape, and robbery at such a higher rate than their counterparts in other nations, display such a curious reluctance to perpetrate burglaries, particularly against occupied residences? Could the answer be that they are afraid of getting shot? When an American burglar strikes at an occupied residence, his chance of being shot is equal to his chance of being sent to jail. Accordingly, a significant reduction in the number of Americans keeping loaded handguns in the home could lead to a sharp increase in the burglary rate, and to many more burglaries perpetrated while victim families are present in the home.[1]

3.                    (Copi Introduction to Logic, p. 500)

The passage that follows contains an explanation.

a.                   What data are to be explained?

b.                   What hypotheses are proposed to explain them?

c.                   Evaluate the hypothesis in terms of the criteria for Evaluation of Explanations in the last lecture.

            Void

Again, however solid things are thought to be, you may yet learn  from this that they are of rare body; in rocks and caverns the moisture of water oozes through and all things weep with abundant drops; food distributes itself through the whole body of living things; trees grow and yield fruit in season, because food is diffused through the whole from the very roots over the stem and all the boughs. Voices pass through walls and fly through houses shut, stiffening frost pierces to the bones. Now if there are no void parts, by what way can the bodies severally pass? You would see it to be quite impossible. Once more, why do we see one thing surpass another in weight though not larger in size? For if there is just as much body in a ball of wool as in a lump of lead, it is natural it should weigh the same, since the property of body is to weigh all things downwards, while on the contrary the nature of void is ever without weight. Therefore when a thing is just as large, yet is found to be lighter, it proves sure enough that it has more of void in it; while on the other hand that which is heavier shows that there is more of body and that it contains within it much less of void. Therefore that which we are seeking with keen reason exists sure enough, mixed up in things; and we call it void.[2]