The traditional dramatic monologue elements of both poems have the characters speaking to someone else ("you"), but Prufrock, the weaker of the two, has less control over the course of his monologue. Unintentionally, Prufrock and the Duke both reveal their true ability to love through contrasts and discrepancies in their speech.
The Duke in "My Last Duchess" gradually proves himself to be egomaniacal and possibly homicidal. He wants to marry, but his idea of love, much like his idea of art, is that it should exist to glorify him above all else. He found his last duchess, whose heart was "too soon made glad" (line 21), "too easily impressed" (line 23). Her smile, he felt, should be reserved solely for him, and in his determination to stop her from experiencing joy from every pleasant thing in life, he commanded her until "all smiles stopped together" (line 46). Now she exists only in a painting "as if alive" (line 47), implying that she is, in fact, alive no longer, and the audience cannot help but suspect her death came at his hands. As the Duke negotiates for the procurement of his next duchess, he exhibits the same attitude as a man today would discuss the purchase of his next car. To the Duke, love is a commodity inherent in women, something to be bought and sold, and discarded if defective.
In contrast, Prufrock does not