Why doesn't he know the cause of his sadness? What guesses do Solanio and Salerio have about the causes of his depression? What lifts his depression?
Antonio, a merchant, is in a melancholic state of mind and unable to find a reason for his depression. Solanio suspects Antonio is worried about his ships at sea with all their cargo but Antonio denies this reason. This unexplained melancholy is common in Shakespeare's plays. Still one could speculate that Antonio is self-absorbed. I always thought he is merely lonely. Helping Bassanio with his gamble (wooing Portia) seems to help.
I believe Antonio is in a melancholic state because there is nothing to make him happy . His merchandise doesn't seem to worry him. He also thanks his fortune that not all his business enterprises are risked in a single ship nor to any place. Nor does his financial position depend on the venture of this year . His state of mind changes into a fairly cheerful one when he begins to converse with Bassanio.
