sanyalpritish wrote:A theory is either true or false. Galileo's observations of Jupiter's satellites showed that the Ptolemaic theory of the motion of celestial bodies is false. Therefore, since the Copernican theory of planetary motion is inconsistent with the Ptolemaic account, Galileo's obseravations of Jupiter's satellites proved the truth of the Copemican theory.

The argument above is open to the objection that it makes the questionable assumption that

a. whoever first obeserved something inconsistent with the truth of the Ptolemaic theory should be credited with having proved that theory false
b. there are some possbile observations that would be inconsistent with the account given by the Copernican theory but consistent with the account given by the Ptolemaic theory
c. the Ptolemaic theory and Coperrican theories, being inconsistent, cannot both be based on exactly the same evidence
d. numerous counterexamples were necessary in order to show the Ptolemaic theory to be false
e. the Ptolemaic and Copernican theories , being inconsistent, cannot both be false

Why is C wrong

Testluv wrote:The correct answer is definitely choice E, and liferocks' reasoning is good.

Just because an observation is inconsistent with the Ptolemaic account doesn't establish that it is consistent with (or will verify) the Copernican account. The observation can be inconsistent with both the Ptolemaic and the Coperncian theory--unless you assume that there is no other possibly correct theory. And that's what the author assumes--that both theories cannot be false (ie, that there is no ohter possibly correct theory).