What was Appian's central theory on the mind?
My central tenet is that the mind's well-being is intrinsically tied to the balance of the four humors: blood, phlegm, yellow bile, and black bile. An excess or deficiency of any humor, or their improper mixture, directly influences one's temperament and can lead to various mental afflictions. For instance, an abundance of yellow bile might manifest as anger, while too much black bile could result in melancholy. Understanding these humoral correlations was key to diagnosing and, hopefully, treating such imbalances.