A theory is either true or false. Galileo's observations of Jupiter's satellites showed that the Ptolemaic theory of the motion...
GMAT Critical Reasoning : (CR) Questions
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 observations of Jupiter's satellites proved the truth of the Copernican theory.
The argument above is open to the objection that it makes the questionable assumption that
Passage Analysis:
| Text from Passage | Analysis |
| A theory is either true or false. |
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| Galileo's observations of Jupiter's satellites showed that the Ptolemaic theory of the motion of celestial bodies is false. |
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| Therefore, since the Copernican theory of planetary motion is inconsistent with the Ptolemaic account, Galileo's observations of Jupiter's satellites proved the truth of the Copernican theory. |
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Argument Flow:
The argument starts with a simple rule (theories are either true or false), then shows one theory is false (Ptolemaic), and concludes that a different theory must be true (Copernican) because it disagrees with the false one.
Main Conclusion:
Galileo's observations proved that the Copernican theory is true.
Logical Structure:
This is a flawed either/or argument. The author assumes that if one theory is false and another theory disagrees with it, then the second theory must be true. But there could be multiple theories that all disagree with the Ptolemaic theory, or the Copernican theory could be wrong for entirely different reasons than the Ptolemaic theory.
Prethinking:
Question type:
Assumption - We need to find what questionable assumption the argument makes. This is asking us to identify a flaw in the reasoning that the author takes for granted.
Precision of Claims
The argument deals with absolute claims about theories being true or false, and makes a definitive conclusion that Galileo's observations proved the Copernican theory true.
Strategy
Look for gaps in the logical reasoning. The argument jumps from 'Ptolemaic theory is false' and 'Copernican theory disagrees with Ptolemaic theory' to conclude 'Copernican theory must be true.' We need to find what the author assumes to make this leap work.
This focuses on who should get credit for disproving the Ptolemaic theory, but the argument isn't about giving Galileo credit for disproving Ptolemy. The argument is about using Galileo's observations to prove Copernican theory true. The assumption we're looking for relates to the logical leap from 'Ptolemaic is false' to 'Copernican must be true,' not about who deserves credit for discoveries.
This suggests the argument assumes there are observations that would support one theory over the other. However, the argument doesn't rely on this assumption. The author's reasoning doesn't depend on whether there could be distinguishing evidence between the theories - it simply uses the fact that one theory is proven false to conclude the other must be true.
This states that inconsistent theories cannot be based on the same evidence. But the argument doesn't assume anything about what evidence the theories are based on. The author's logic centers on the relationship between the truth values of the theories, not their evidential foundations.
This assumes multiple counterexamples were needed to disprove Ptolemaic theory. But the argument actually suggests that Galileo's single set of observations was sufficient to prove Ptolemaic theory false. The author doesn't assume that numerous counterexamples were necessary - quite the opposite.
This captures the critical flaw in the argument's reasoning. The author assumes that because these two theories are inconsistent with each other, they cannot both be false. This assumption allows the author to conclude that if Ptolemaic theory is false, then Copernican theory must be true. But this is questionable because both theories could be wrong - there might be a third, correct theory that we haven't considered. The author treats this as a simple either/or situation when it's actually more complex.