Chaucer believes that the doctor knows all of his medical knowledge by heart. Chaucer does bring up the fact that a lot of the doctor's medical decisions are based on astrology and the four humors though. The four humors are sanguine, choleric, phlegmatic, and melancholic. Chaucer criticizes him about the fact that he does not know bible very well. Chaucer believes that the doctor is greedy because he hands out fake cures for the Black Plague to make a bunch of money. Chaucer jokes that the doctor's favorite medicine is gold.