Strepsiades's day in court grows near and he goes to retrieve Pheidippides from Socrates's school. Socrates assures him that the school has shaped Pheidippides into a brilliant speaker and thinker, able to wriggle his way out of any impossible pinch. Strepsiades whoops for joy and fawns about Pheidippides. Pheidippides, however, does not share Strepsiades's enthusiasm, but rather starts immediately to question the very premise of the day of "Old and New" (II.i.1153), the day when debts are due. Using his Socrates-influenced methodology, he systematically destroys the notion that a day could be both "Old and New." Strepsiades is flustered and hardly seems to know what to do with his new and improved son, but the two adjourn to celebrate their reunion and plot their case.

Almost instantly the First Creditor is at their door, wanting to haul Strepsiades to court. Strepsiades, cocky because he believes in his son's powers of persuasion, answers the First Creditor and ridicules him because of his belief in the gods and because of his nonsensical adherence to the paradoxical day of "Old and New" (II.i.1153). He quizzes the First Creditor about the proper name and gender for a "trough" (II.i.1255). The First Creditor is flustered and indignant. Strepsiades imperiously sends him off because of his gross "ignoran[ce]."

A Second Creditor arrives, but instead of berating Strepsiades for his failure to pay, the Second Creditor moans and wrings his hands in a melodramatic display of neediness. Strepsiades also sasses the Second Creditor, asking him about his thoughts on the mechanism of rain. When the baffled Second Creditor demands his loan plus interest, Strepsiades refutes his accrual of interest with the example of the sea, which he says is always full of new water but never increases in size. Strepsiades proceeds to beat the Second Creditor and chases him off.

The Chorus of Clouds interrupts with a song that judges Strepsiades, noting his new passion for dishonesty and promising that he will be brought low because of this "wickedness" (II.i.1303). The Chorus prophesizes that Strepsiades will prove his own undoing: that he has educated his son in the slippery arts of immoral persuasion with which his son will in turn harm him.

As the Chorus finishes its dire prediction, Strepsiades races from the house, pursued by Pheidippides who is beating him. The two had bickered over the recitation of traditional poetry and their argument came to blows. They decide to have a formal debate to prove who is right and who is wrong. Strepsiades recounts his evening arguments with Pheidippides, explaining his shock that his son is not obedient or respectful towards him, always using every instance as an opportunity to attack Strepsiades and his tastes. Strepsiades accuses Pheidippides of being ungrateful, recalling the tender and special relationship they had when Pheidippides was a needy infant. Strepsiades argues that such nurturing and sacrifice on his part should have earned him Pheidippides's respect and high regard. Pheidippides relishes his new rhetorical abilities and wonders aloud about his past fascination with horses. Strepsiades ruefully adds that he wishes his son was still mad for horses—although it was this very obsession that landed Strepsiades in such a financial pickle.

Pheidippides argues that he has hit his father for Strepsiades's own good, that any prior laws dictating standards of behavior and deferral to parental authority are fallible and subject to change. He invokes examples of animal behavior. He threatens to include his mother in his argument and Strepsiades bemoans his choice to educated Pheidippides. Strepsiades turns to the Chorus of Clouds and berates the Chorus for encouraging the folly of educating Pheidippides in the Unjust argument. The Chorus of Clouds asserts that Strepsiades earned what he got and that the Chorus has strung him along in order to prove to him the folly of his ways and beliefs, to teach him to respect "Heaven's holy laws" (II.i.1458).