Equality
Gay's exploration of equality has an inherent irony to it, and understanding this irony is essential to appreciating the sharpness of his satire. Both explicitly through dialogue and implicitly through the story, Gay critiques the outright inequality between the rich and poor. However, what makes the work unique is that he makes incessant comparisons between the powerful rich and the desperate poor. His basic idea is that
despite social class, all men are naturally self-interested and corrupt. The text is rife with humorous equivalencies drawn between statesmen and criminals, lawyers and impeachers, highwaymen and courtiers, all to suggest that inequality is due as much to how hypocritical a man is willing to be, and not to his virtue.
Marriage
In the world of The Beggar’s Opera, marriage bears no resemblance to the romantic notion of a holy union between two soulmates. Instead, Gay continually mocks this notion, suggesting that love is more closely aligned with lust and self-interest than with selflessness.
The closest Gay comes to representing the idealized conception is in the profuse professions Polly and Lucy make for Macheath. However, both women are as focused on physical intimacy as upon a transcendent union. Polly's marriage ultimately means little to Macheath, and most characters think of it is in terms of its financial benefits, with little thought of her emotions. The girls’ notion of romantic love, so misplaced upon an obvious cad, renders the romantic ideal ludicrous.
For the rest of the characters, a woman’s only use for marriage is financial security -resting on the hotly-anticipated death of the male spouse, from whom she might inherit. Freedom of sexual expression is also put forward as a potential benefit of marriage, far different again from the romantic notion of monogamy. Once married, a wife’s reputation is vouchsafed by her husband. She may thus act with impunity, according to her whim. All of these representations were unique in the time period, and helped to make Gay's work so transgressive.
Friendship
There are myriad instances of friendship in the opera, although none of them conform to the ideal notion of a selfless affection for another. Instead, most characters are quick to betray even the most seemingly profound of relationships. As a virtue, friendship is espoused by: Peachum for Lockit (and vice versa); the highwaymen for each other; the harem of ladies for one other; Mrs. Peachum for her favorite gang members; and even Lucy for Polly. In each case, though, the affection proves at best a transitory kind of fidelity, dictated utterly by self-interest. The highwaymen congratulate themselves on their valiant allegiance and dedication to one another, but in the next moment conspire to “befriend” unsuspecting victims about the town in order to rob them. Mrs. Peachum inquires after the wellbeing of her favorite gang members, extolling their virtues, but quickly drops her concern upon discovering that her husband has chosen them for the current session’s impeachment. For Peachum and Lockit, as for Lucy and Polly, friendship is a self-consciously insincere tool. Peachum and Lockit are business partners and self-proclaimed friends, yet each man seeks to cheat the other. Lucy offers a conciliatory glass of cordial to Polly in seeking to forgive the past and forge a future friendship...and the cordial is poisoned.
Hypocrisy
Hypocrisy is arguably Gay's most significant target in the opera. Both implicitly and explicitly, he mocks the way that statesmen reach great heights not through virtue, but through their hypocrisy. In fact, hypocrisy defines each and every character, action and employment, suggesting it is an inherent, inescapable human quality. Gay's lyrics are the best place to find witty articulations of his time's hypocrisy. When Peachum expresses the view that it might be reasonable to consider their line of work dishonest, Lockit responds with a display of indignation, singing:
When you censure the age
Be cautious and sage,
Lest the courtiers offended should be;
If you mention vice or bribe,
‘Tis so pat to all the tribe;
Each cries—That was levell’d at me. (p. 42)
Lockit’s sentiment encapsulates the simple truth that there is falseness in every heart, verified by the indignation of its denial.
“Live for To-day”
The criminal mindset is greatly bolstered by the view that tomorrow may never come. It is not just criminals who use such reasoning to justify morally ambiguous actions, of course. Instead, Gay suggests that we all encounter situations where we compromise ourselves for the sake of momentary gratification. (Consider the scene between Lucy and Polly.) The morally bankrupt characters of The Beggar’s Opera, however, take a sanguine view of the matter: The noose is in everyone’s future. Thus, let us live for today. While Gay does not explicitly comment on living one's life through this philosophy, he does implicitly suggest that it is a natural human rationalization.
The Law
There is no question that the profession receiving the worst review in The Beggar’s Opera is law enforcement. The officers of the Court are bribable men who regularly suppress evidence in criminal prosecution for the right price. Quite explicitly, justice is for sale, and a malleable concept at best. Worst of all are the lawyers, repeatedly invoked throughout the play as the prime example of those who profit by the vice of others. One day they protect the unsavory; the next, they prosecute them. It all depends on the price. If anything serves as an immovable law in The Beggar's Opera, is the natural law of human selfishness.
Self-Awareness
The characters in The Beggar’s Opera are prone to a philosophical defensiveness against their own dishonesty. It is as though they are aware of and armed against the audience’s gaze. This defensiveness utilizes deflection: the characters often confess their own moral failings or treachery, but then divert the attack to their social betters. If murder is wrong, for example, then look to the “gentlemen” who have the money to employ assassins or pay off the police. If Macheath has a gambling problem, blame the gentlemen at the same table, whose educations prepare them more properly for the games and whose pocketbooks may more easily take a hit. Gay implicitly suggests in his play that we would all do better to look closely at ourselves, rather than to define ourselves by others - since others will naturally and regularly give us much occasion to defend our own vices and failures.
