Like Aristotle, Ibn Khaldūn saw cyclicity in history, its cycles overlaid on scripture's linear visions of time from creation to the last day. Within these cycles a dialectic was at work: 'aṣabiyya, tribal spirit, sublimated by a unifying religious fervor, could energize new dynastic powers that would promote a blossoming of urban civilization. But that efflorescence led inexorably to loss of the desert virtues of self-reliance and solidarity and an inevitable fall. History's ever renewed tragedies wrought judgment on both tribal and urban groups through the strengths and weaknesses of character endemic in their condition. Ibn Khaldūn's profound and original conception was built on a synthesis he framed, of Plato's account of the dissolution of the kallipolis with the biblical warnings he knew, that the sins of forebears are visited on their off spring to the third and fourth generation.