“I gave both the dog and the cat some vitamin D,” the experimental scientist says to himself, “and both their skin rashes went away.” This discovery leads him to make a hypothesis: Whenever an animal with a skin rash is given this amount of vitamin D, it will be cured. He will be able to reexamine old cases—“I saw a dog the other day eat some broccoli and its skin rash disappeared, so broccoli must contain vitamin D”—and open the way to considering new ones. When he gives vitamin D to his spouse and her skin rash actually gets worse, he doesn’t throw up his hands in despair. He wonders why
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