Passage Summary: People think poems are good because they are 'true,' but that's wrong. Most things people believe are true, and since being 'excellent' means being special or rare, just being true isn't enough to make a poem great.

Conclusion: Expressing true propositions does not contribute to the aesthetic merit of a poem.

Reasoning: Most common beliefs are true, and since the basis of excellence must be rare, truth (which is common) cannot be the basis for excellence.

Analysis: The statement that excellence must be rare serves as a general principle or premise. The author uses this principle to dismiss 'truth' as a factor in aesthetic merit: if truth is common and excellence is rare, truth can't be what makes something excellent. It's the logical bridge that connects the fact about common beliefs to the rejection of the 'truth equals merit' argument.