In this crucial, sensual sonnet, the young man becomes the "master-mistress" of the poet's passion. The young man's double nature and character, however, present a problem of description: Although to the poet he possesses a woman's gentleness and charm, the youth bears the genitalia ("one thing") of a man, and despite having a woman's physical attractiveness, the young man has none of a woman's fickle and flirtatious character — a condescending view of women, if not flat out misogynistic.
The youth's double sexuality, as portrayed by the poet, accentuates the youth's challenge for the poet. As a man with the beauty of a woman, the youth is designed to be partnered with women but attracts men as well, being unsurpassed in looks and more faithful than any woman.
Sonnet 20 is the first sonnet not concerned in one way or another with the defeat of time or with the young man's fathering a child. Rather, the poet's interest is in discovering the nature of their relationship. Yet even as the poet acknowledges an erotic attraction to the youth, he does not entertain the possibility of a physical consummation of his love.
Of all the sonnets, Sonnet 20 stirs the most critical controversy, particularly among those critics who read the sonnets as autobiography. But the issue here is not what could have happened, but what the poet's feelings are. Ambiguity characterizes his feelings but not his language. The poet does not want to possess the youth physically. But the sonnet is the first one to evoke bawdiness. The poet "fell a-doting" and waxes in a dreamlike repine of his creation until, in the last line, the dreamer wakes to the youth's true sexual reality: "Mine be thy love, and thy love's use their treasure." We are assured then that the relation of poet to youth is based on love rather than sex; according to some critics, even if the possibility existed that the poet could have a sexual relationship with the young man, he doesn't show that he would be tempted. Other critics, of course, disagree with this interpretation.