How does the speaker in Shakespeare's "Sonnet 18" answer his own question?The speaker opens the sonnet by wondering if he should compare his...

The speaker first asks if he shall compare the person he
loves (thee) with a summer’s day. He then does just that. It is almost like he is saying
“I will now compare thee to a summer’s day.” By starting the sonnet with a question, he
invokes a sense of respect to the person he is speaking about. He may be alone and just
speaking rhetorically. But if he’s addressing this person, he is asking permission to
make this comparison, knowing she/he will acquiesce.

The
speaker then proceeds to describe how his loved one is more lovely and everlasting than
the beauty he sees in nature. The speaker never rejects the comparison. He uses the
comparison to show his favoritism for his loved one over
nature.

In an indirect way, you could say he rejects the
comparison because it is through the lines of this sonnet that his loved one lives on.
In other words, the eternal summer of his loved one will never fade but that’s because
this poem will survive long beyond her death.  So, it is the sonnet itself that never
fades. The speaker is talking about the beauty of this person, but the comparison
between his loved one and a summer’s day is used to make the point that it is the
poetry, not the beauty itself, that provides this longer life.