Alone, Posthumus rails against women. He claims that due to their frailty and sexual infidelity, women only give birth to illegitimate children. He thinks that his mother appeared to his father like the chaste Diana, and so too did Imogen appear chaste to him. He swears revenge. He comments that Imogen would often prevent Posthumus from having sex with her (presumably before marriage), and she asked him to refrain from lust. He claims she asked so sweetly that even a god would have found it attractive. Posthumus says he was sure she was as pure as unmelted snow.
Iachimo has twisted Posthumus’ mind to such an extent that what Posthumus had once considered to be a virtue of Imogen—her chastity, putting off Posthumus’ sexual advances (most likely before marrying)—has become a vice, since he thinks she was sexually loose with Iachimo. In this infamous misogynistic speech, Posthumus generalizes that women are adulterous liars.
Posthumus wonders how long it took for Imogen and Iachimo to go from just meeting to having sex—was it an hour, or less? He imagines that Iachimo barely spoke to Imogen before they went headlong into the act, and that she put up no resistance. He lists all of women’s flaws, including lying, flattery, deceit, lust, revenge, ambition, jealousy, and more. He claims that the only thing women are “constant” to is “vice.” Posthumus swears vengeance and promises to further meditate on the evil of women.
Reminiscent of speeches from Othello, Posthumus’ speech is poisoned by jealousy. He has gone beyond Iachimo’s “proof” to obsessively imagine Iachimo and Imogen’s sexual encounter, which troubles Posthumus all the more. Again, he makes striking generalizations about women, and his vows of revenge have Posthumus sounding more like Cloten—an inherently bad, ignoble example to follow.