A Chinese philosophy based on the writings of Lao-tzu, advocating humility and religious piety. The central concept and goal is the Tao, and its most important text is the Tao-te-Ching. Taoism has both a philosophical and a religious aspect. Philosophical Taoism emphasizes inner contemplation and mystical union with nature; wisdom, learning, and purposive action should be abandoned in favour of simplicity and wu-wei (non-action, or letting things take their natural course). The religious aspect of Taoism developed later, c.3rd century ad, incorporating certain Buddhist features and developing a monastic system.