What were Galen's four humors?

Blood (sanguine, hot/moist), yellow bile (choleric, hot/dry), black bile (melancholic, cold/dry), and phlegm (phlegmatic, cold/moist). Imbalance was thought to cause illness and mood disorders.

Why did the four humors model fail scientifically?

The biological mechanism was incorrect; we now know neurotransmitters, genetics, and brain structure underlie personality. However, the behavioral archetypes identified remain remarkably predictive in modern research.

Is there modern scientific support for Galen's categories?

Yes. Contemporary research confirms the four temperament categories reflect real behavioral patterns. Modern frameworks like Big Five and Keirsey validate these ancient insights using updated science.

How did Galen's theory influence medical practice?

For 1500+ years, physicians treated imbalance through bloodletting, diet, herbs, and environment. While methods were harmful, the principle of matching treatment to individual temperament influenced personalized medicine concepts.