Why did ancient Greek philosophers believe music could affect human character and behavior?

Ancient Greek philosophers believed that music possessed the power to influence human character and behavior through the doctrine of ethos. This concept was rooted in the belief that music exerts a direct effect upon the human soul and actions.1

Philosophers like Plato viewed music as a department of ethics and argued that it reflected the moral order of the universe. Because they believed music echoed divine harmony and that its rhythms and melodies imitated the movements of heavenly bodies, they concluded that specific musical modes could either cultivate virtue or lead to disorder and depression. Consequently, Plato advocated for strict regulation and censorship of music to ensure it remained in an ethically approved form.2

Aristotle also maintained that music could mold human character, though he held a more inclusive view than Plato, suggesting that a wider variety of modes could provide value to both the individual and the state. Ultimately, this belief established music as a fundamental, psychosociological force in Greek society, deeply integrated into education and political life.21