Buddhists regard the doctrine of rebirth not as a mere theory but as a verifiable fact. The belief in rebirth forms a fundamental tenet of Buddhism. However, the belief in rebirth is not confined to Buddhists; it is also found in other countries, in other religions, and even among free thinkers. Pythagoras could remember his previous birth. Plato could remember a number of his previous lives. According to Plato, man can be reborn only up to ten times. Plato also believed in the possibility of rebirth in the animal kingdom. Among the ancient people of Egypt and China, a common belief was that only well-known personalities like emperors and kings have rebirths. A well-known Christian authority named Origen, who lived in 185-254 A.D., believed in rebirth. According to him, there is no eternal suffering in hell. Gorana Bruno, who lived in the sixteenth century, believed that the soul of every man and animal transmigrates from one being to another. In 1788, a well-known philosopher, Kant, criticized eternal punishment. Kant also believed in the possibility of rebirth in other celestial bodies. Schopenhauer (1788-1860), another great philosopher, said that where the will to live existed there must be of necessity life. The will to live manifests itself successively in ever new forms. The Buddha explained this ‘will to exist’ as the craving for existence.