Così fan tutte is an opera buffa in two Acts by the Austrian composer, Wolfgang Amadeus Mozart, who is also known for his many symphonies and other operas, including Don Giovanni, The Magic Flute, and The Marriage of Figaro. Così fan tutte was composed in 1789 with an original libretto by Lorenzo da Ponte, who also provided the librettos for The Marriage of Figaro and Don Giovanni, The premiere of Così fan tutte took place in 26 January 1790 at the Burgtheater in Vienna.
The story of Così fan tutte is set in eighteenth century Naples and takes place within a single day. It involves the romance of two officers, Ferrando and Guglielmo with two sisters, respectively Dorabella and Fiordiligi. An old cynic, Don Alfonso, hearing the men praise the women, tells them that there is no such thing as a faithful woman, and when they argue, proposes a bet. He wagers that if they leave for a single day, the sisters will prove unfaithful, which he proposes to show them by having them pretend to leave, return in disguise, woo the sisters, and see what happens.
The sisters are distraught at the departure of the men, and after bidding them farewell, explain the situation to their maid, Despina, who is shortly brought into the wager by Alfonso. The two soldiers enter in disguise, pretend to be poisoned, and are left to the sisters’ care, while Despina and Alfonso go for help, bringing back Despina in disguise as a doctor who pretends to cure the men. The revived men request a kiss from the sisters, who both refuse.
In Act II of Così fan tutte, the men continue the siege, but with the disguised Ferrando pursuing Fiordiligi, and Guglielmo making headway with Dorabella. Before long, the men succeed so well, that a lawyer, Despina in disguise again, is sent for to draw up marriage contracts. Don Alfonso makes a well-timed entrance to announce the soldiers’ return — just before the contracts are signed. The disguised men flee and reenter as themselves and Don Alfonso hands them the marriage contracts as proof of their betrayal. Things seem to be at an impasse, until Don Alfonso reveals the wager.
Così fan tutte ends with the couples paired off, but there is no indication in either the libretto or the music to decide whether it is the original couples or the formed when the men were in disguise. This leaves the director to decide how the opera should end in each performance.