On a street in Venice, the merchant Antonio tells his friends Solanio and Salerio that he feels "so sad" (1.1.1) but doesn't know why. Salerio proposes, with Solanio's agreement, that Antonio must be worried about his ships at sea. But Antonio insists that he's confident his ships are safe. Then, Salerio guesses, Antonio must be in love. Antonio dismisses this possibility at once. Salerio concludes, jokingly, that if Antonio is neither worried about his investments, nor melancholy because of lovesickness, then he must simply be "sad because [he] is not merry" (1.1.47–8). Salerio advises him to shake off his bad mood because it would be just as easy "to say you are merry because you are not sad" (1.1.49–50).
By emphasizing that he doesn't know the cause of his sadness, Antonio creates mystery around his character—mystery that demands that other characters "interpret" what's wrong with him. Some critics feel that Antonio's forceful denial that his sadness has anything to do with love actually hints that it does have to do with love. Salerio's conclusion that Antonio's mood is simply a whim, which can be changed by changing perspective, further underscores how different interpretations can create vastly different outcomes.
Bassanio, a relative and close friend of Antonio's, enters with his friends Lorenzo and Gratiano. After politely greeting the newcomers, Solanio and Salerio exit.
Polite manners cement friendly relationships between the noblemen of Venice.
Lorenzo and Gratiano announce that they must depart, but will see Bassanio again at dinner. Before leaving, though, Lorenzo notes that Antonio looks unwell. Antonio responds that, on the "stage" of the world his part is to be "sad" (1.1.78–9). Gratiano interrupts that he would rather play the happy role of a "fool" (1.1.79) and teases Antonio, telling him to lighten up. Lorenzo reproaches Gratiano for talking too much and repeats that they will rejoin Bassanio for dinner. They exit.
Antonio's comment about the stage and that it is his "part" to be sad indicates that there is some mysterious aspect of his personality that ensures his sadness. Gratiano's crass jokes reveal him to be less sensitive—despite the fact that he's a noble Venetian. Throughout the play, his bad manners raise the question about who is civilized and who is not.
Once alone, Bassanio apologizes for Gratiano's insensitivity and reveals why he's come to see Antonio. He is in love with Portia, a wealthy noblewoman, and hopes to seek her hand in marriage. However, he lacks the financial means to do so. He has many debts he must clear before he can woo her, including debts to Antonio.
That Bassanio needs cash to woo Portia introduces a connection between love and money that will persist throughout the play. That he already owes Antonio money hints that he is willing to use his friend for material purposes.
Antonio replies that he will do anything for his friend and is happy to place both his "purse" and his "person" at Bassanio's disposal. Though Antonio has no cash available at the moment because he's invested everything in his ships currently at sea, he says that Bassanio can use his "credit" (Antonio's known wealth and good reputation) in order to get a loan from someone else in Venice.
Bassanio's ulterior motives contrast with the pure devotion and generosity of Antonio's friendship. In fact, Antonio acts so selflessly toward Bassanio that many critics argue that Antonio is actually in love with Bassanio. These critics think Antonio's sadness results from his unrequited love.