Final answer:
Galen added to Hippocrates' four personality types the idea that each type reflects an excess of some bodily fluid, corresponding to the four temperaments: choleric, melancholic, sanguine, and phlegmatic.
Step-by-step explanation:
Galen expanded on Hippocrates's theory of personality types by suggesting that diseases and personality differences could be attributed to imbalances in the four bodily fluids. These fluids correspond to the four temperaments: choleric (yellow bile), melancholic (black bile), sanguine (red blood), and phlegmatic (white phlegm). Each temperament described a distinct personality type, with the choleric being passionate and ambitious, the melancholic being reserved and anxious, the sanguine being joyful and optimistic, and the phlegmatic being calm and reliable. Galen believed that every person exhibited one of these temperaments, which were indicative of an excess of a particular bodily fluid.