As blushing will sometimes make a whore pass for a virtuous woman, so modesty may make a fool seem a man of sense.

Swift draws a deliberately shocking parallel to argue that society routinely confuses external demeanor with inner worth. Blushing, a bodily sign associated with shame or innocence, can be performed or misread, enabling a “whore” to be taken for virtuous; likewise, modesty—silence, self-effacement, cautious speech—can be mistaken for wisdom, allowing a fool to seem sensible. The sting of the sentence is its insistence that social judgment is often lazy: people infer moral purity or intelligence from mannerisms rather than evidence. Swift’s satire warns readers to distrust appearances and to recognize how easily “virtue” and “sense” can be counterfeited by the right performance.