Explanationism is the idea that prediction is, in itself, insufficient to confirm a theory. To adequately confirm a theory, according to an explanationist, is to see how well it describes events and phenomena that have already been observed. Take, for example, the difference in the perspectives of Copernicus and Brahe on the solar system. Copernicus's model of the solar system 5 was heliocentric, positing that all of the planets revolved around the sun. Brahe's theory stated that all of the planets revolved around the sun, except the earth, which was immobile, and that the sun actually revolved around the earth. Even if both accurately predicted future movements of the planets, it is easy to see how Copernicus's theory has less of an "ad hoc" quality. It is certainly true that a theory can successfully predict a certain event, yet fail to provide an adequate explanation 10 for why it happened.

A predictionist would argue that while a theory can provide a perfect explanation for something happening, a theory cannot be tested for understanding or explaining the underlying mechanism of a phenomenon unless it can also predict some event that confirms that exact mechanism at work. For instance, a physicist studying solid formation may suggest all solids 15 sink in a liquid of the same element due to their higher density. Given this premise, even once he stages an experiment with ice and water, he will not be proven wrong, but rather will have discovered a unique property of solid water.

Which of the following best expresses the main idea of the passage?

(A) Explanationism is a superior theory to predictionism.
(B) Two very different ideas can both be used to successfully investigate scientific theories.
(C) Copernicus's model of the solar system was more accurate than Brahe's due to explanationism.
(D) One cannot posit a physical theory without predictive power or previous observations.
(E) A predictionist and an explanationist will always diverge on whether a scientific theory is correct.



Which of the following most accurately states the author's reason for citing the Copernicus and Brahe models of the solar system?

(A) It shows that a theory without predictive power can never be tested and verified.
(B) It reveals that some theories can have more or less of an "ad hoc" quality.
(C) It shows that two different theories can never yield the same predictions for future events.
(D) It is used to support the idea that a more complicated model will always fail to a simpler model.
(E) It provides an example of when a theory can correctly predict future events but not offer the best explanation.