Passage Summary: The author argues that if a scientist 'fudges' their theory to match a known fact, that fact shouldn't be used as proof that the theory is actually correct.

Conclusion: The advance of the perihelion of Mercury should not be considered valid evidence for Einstein's theory of general relativity.

Reasoning: Einstein was already aware of the phenomenon and likely adjusted his mathematical equations specifically to fit the known data.

Analysis: The argument relies on a specific standard for what counts as scientific evidence: it suggests that 'post-hoc' data fitting (adjusting a theory to match known results) is illegitimate. To justify this conclusion, we need a principle that formalizes this requirement. Look for an answer that states a theory is only truly supported by data it predicts successfully without that data being used to build the theory. This would bridge the gap between Einstein's 'adjustment' and the dismissal of the evidence.