But Famusoff settles the matter by declaring that it comes from knowing too much.

This takes place at an evening party at the Famusoffs, and Tchatsky returns to the room to meet with an amazing reception.
Eventually, he discovers that he is supposed to be mad, and that he is indebted to Sophia for the origin of the lie; also, that she is making rendezvous with the low-minded, flippant Moltchalin.

At last Sophia discovers that Moltchalin is making love to her maid through inclination, and to her only through calculation.

She casts him off, and orders him out of the house.

Tchatsky, cured of all illusions about her, renounces his suit for her hand, and declares that he will leave Moscow forever.