Before the first story of the fourth day begins, Boccaccio provides a story of his own. He complains about his critics, defends his use of the much-maligned “Florentine” (515) dialect of the Italian language, and rejects claims that he is overly fond of women. To illustrate his point, he tells the story of Filippo Balducci, a lowborn man who married a woman and had a child. When the woman died, Filippo “resolved to withdraw from the world and devote his life to the service of God” (517). He and his son live pious lives in a cave in the country. When his son is 18, Filippo agrees to take him into Florence for the first time. Despite Filippo's best efforts, his son is enamored with women. Filippo knows that he will not be able to dissuade his son from his natural interest in women. Boccaccio has “no desire to carry this tale any further” (519) and rejects his critics once again.

On the fourth day, Filostrato is made king. For a theme, he chooses loves that end unhappily.

The first storyteller is Fiammetta. Tancredi is the Prince of Salerno. His beloved daughter Ghismonda married the Duke of Capua but, when the Duke died, she returned to her family.