Ibn Sina (Avicenna)

The bile is the humor of anger and courage.

The phlegm is the humor of calmness and patience.

The black bile is the humor of melancholy and sadness.

The blood is the humor of joy and love.

The four humors must be in balance for health to be maintained.

The imbalance of the humors is the cause of disease.

The treatment of disease must aim to restore the balance of the humors.

The use of drugs is a last resort when diet and lifestyle changes fail.

The best medicine is prevention.

The physician must be a philosopher, for philosophy and medicine are sisters.

The proof that the soul is immortal is that it can conceive of immortality.