# scientific reasoning

Read Inference to the Best Explanation and Judging Scientific Theories (Module 14).
Read excerpt from Philosophy of Natural Science by Carl Hempel (3-8).

1. What are the steps in the scientific method? (2 pts)

2. What is the problem (phenomenon to be explained) that Ignaz Semmelweis confronted at the Vienna General Hospital between 1844 and 1848? (You need to mention what is going on in the First Maternity Division and what is going on in the Second Maternity Division in the same hospital, but you can be brief.) (2 pts))

3. Semmelweis considered about ten explanations (theoretical explanations/theories/
hypotheses) for the problem. He considered these explanations BEFORE he visited the morgue.
State SIX of them. NOTE: A theoretical explanation is a complete sentence (it does not start with “if”). (6 pts)

4. His various explanations are hypotheses that he decided to test. If a certain hypothesis H is true, then certain observable events, I (e.g., decrease in mortality) should occur. I represents the test implication of hypothesis H. In some cases, he found that I, the test implication, turned out to be false and so the hypothesis H was not true.

(Hempel)
If H is true, then so is I.
But I is not true.
H is not true.

This is a valid argument form called modus tollens.

Give THREE EXAMPLES of this deductive form with content from the explanations that Semmelweis was considering. In other words, supply three hypotheses and three test implications and complete the modus tollens argument in each case. NOTE: Semmelweis rejected some of his hypotheses as false because they conflicted with readily observable facts (they were externally inconsistent); so don’t use these to make up your modus tollens arguments. USE: rough treatment by medical students, priest coming to attend dying women, and women’s body position in childbirth.) NUMBER EACH STATEMENT IN EACH ARGUMENT. (9 pts)

5a. What happened that gave Semmelweis an idea about the solution to the problem? (2 pts)

5b. What hypothesis did he come up with? (1 pt)

5c. What new test implication did he come up with? (1 pt)

6. Hempel say that we get a very different situation if I (test implication) turned out to be true. This form of reasoning is deductively invalid. It is the fallacy of affirming the consequent.

If H is true, then I is true.
I is true_______________
H is true.

State Semmelweis’s latest formulation of his reasoning using the form above. NUMBER EACH STATEMENT IN THE ARGUMENT (2 pts)

7a. What happened to make Semmelweis realize that his hypothesis was false? (2 pts)

7b. What is his modified hypothesis? (1 pts)

8. The fallacy of affirming the consequent is still very useful to scientific investigation. Why is it useful? (2 pts)

Take-Home Scientific Reasoning–SOME HELP
NO: If women are lying on their backs in Maternity Ward 1, then they will get puerperal fever and die. = This is just a Hypothesis.

YES: If women lying on their backs in Maternity Ward I causes higher mortality, then changing to the lateral position should decrease the mortality in Maternity Ward 1. =

This is If H, then I. GOOD

NO: If women lying on their backs in Maternity Ward I causes higher mortality, then other women coming into MW1 will also be subject to higher mortality (other women coming into MW1 will also die. = This does not provide a Hypothesis for why the women are dying at a higher rate in Maternity Ward 1.

A women who gave birth on her way to the Vienna Hospital did not develop puerperal fever. INTERESTING FACT—It does NOT show the cause of the deaths, but once the Hypothesis is confirmed (blood poisoning is causing the higher mortality in MW1), it adds more evidence that the Hypothesis is correct.

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