Laws and rules dominate the culture of The Merchant of Venice. Venetian law dictates what people can and cannot do, such as barring Jews from engaging in most professions. It also tends to bend in favor of those in power, as Portia demonstrates in Act 4 when she convicts Shylock (who, up until that point, seemed to have the law on his side). The rules of characters' religions also govern how they conduct themselves.
One example of this occurs in Act 1, Scene 3, when Shylock and Antonio argue about their respective interpretations of the Biblical story of Jacob: Christian Antonio uses the Bible to interpret usury as immortal, while Jewish Shylock does the opposite. Also at play are the rules of wills and bonds. Portia's father's will establishes the casket game and dictates how she will find a husband—a fact that causes her much anxiety, yet works in her favor when Bassanio chooses correctly. The terms of Shylock's loan to Antonio, meanwhile, are at the center of the play and dictate power dynamics—putting Shylock in power when Antonio cannot pay, but stripping Shylock of power under the scrutiny of Venetian law. In the end, those who begin with social and/or monetary power maintain that power, as Antonio, Portia, and Bassanio all emerge even better off thanks to the rules that govern them.
One of the recurring motifs in Merchant is the question of value—in particular, the association between love and currency. Several characters claim to prioritize love in their lives, but they repeatedly speak of it in financial terms. Even the lottery to win Portia’s hand in marriage is determined by gilded caskets, and each suitor’s rationale—including Bassanio's, though much more subtly—is driven by greed and excess. Jessica, too, arrives for her elopement with Lorenzo with a stolen dowry, a reinforcement of the idea that love is manifested in currency; she even lowers the stolen money from the same window she uses to escape, further linking marriage and wealth. Portia and Nerissa also use precious objects—the rings they give to Bassanio and Gratiano—to measure loyalty in love.
Though the play ultimately ends with three marriages, it’s worth noting that romance is offered primarily in economic terms and commitments. Love, in this play, is more calculated and less spontaneous than it may seem, and the characters manifest a world in which fidelity is measured in monetary units. All in all, Shakespeare's use of the motif of love and currency suggests that love is seldom pure and disinterested, and that it often comes with strings attached.
Merchant is filled with contradictions between what is advertised and what lies beneath the surface—that is, it utilizes the motif of appearance versus substance. Portia and Jessica, for example, both cross-dress: Jessica as a torchbearer to escape Shylock's house and elope with Lorenzo, and Portia as Balthazar the lawyer to save Antonio from Shylock's wrath. By taking on new appearances, indeed the appearances of the opposite gender, they both achieve a degree of power that European society did not usually afford to women.
The caskets, too, offer an example of the tension between appearance and substance. The seemingly worst-looking casket, made of "meager lead," contains Portia's image and the right to marry her—making it actually the best casket. Meanwhile, the seemingly most attractive caskets, made of silver and gold, hold the least attractive outcome: losing both Portia and the ability to ever marry. The idiom "all that glisters is not gold" (which is written on a scroll within the golden casket) explicitly draws upon this dichotomy between presentation and inner truth, and reminds the audience of the various other tensions and levels of deception at work in the play. The motif functions, then, to put audiences on notice that not everything is as it appears.
