How is sonnet 55 and sonnet 43 different?

Answer 1

Although both sonnets deal with a contrast, they are different contrasts. Sonnet 43, with its constant imagery of light and shadow, contrasts what we see in dreams with what we see when we are awake. Sonnet 55 contrasts the immortality of the subject of literature with the ephemeral nature even of brick-and-mortar monuments.
In Sonnet 43, Shakespeare is saying that he has clearer vision in dreams because of the presence of the person to whom the sonnet is addressed. If he could only see this person in the day, he would see that much clearer. Its tone is regretful and hopeful; regretful that the person is not present but hopeful that he or she will be, hence "All days are nights to see till I see thee."
In Sonnet 55, however, he is saying that the subject of the poem will live on because he has been immortalized in verse, which outlives even stone monuments. Its tone is exultant, even boastful. "Your praise shall still find room even in the eyes of all posterity that wear this world out to the ending doom."

Answer 2

Sonnet 55 by William Shakespeare celebrates the immortality of the subject's memory through poetry, while Sonnet 43 by Elizabeth Barrett Browning expresses deep, abiding love. Shakespeare's sonnet focuses on the power of verse to extend someone's legacy, while Browning's emphasizes the enduring nature of her love for her partner.