On the Heavens

On the Heavens (Greek: Περὶ οὐρανοῦ; Latin: De Caelo) is Aristotle's major work on astronomy and cosmology, written around 350 BCE. It comprises four books. Book I discusses the nature of the heavens and the completeness and eternity of the cosmos, arguing that the universe encompasses all three-dimensional bodies and is therefore "perfect" and finite, and introducing the fifth element, aether, peculiar to the celestial bodies above the moon. Book II argues that the heavens are spherical, grounding this in geometry and kinematics, and infers from the eternal circular motion of the celestial spheres that there must be a stationary part at the center of the universe—the Earth. Book III turns to the sublunary region, discussing generation and change among the elements and criticizing earlier accounts of elements and motion. Book IV focuses on the lightness and heaviness of the four elements—earth, water, air, and fire—and their natural rectilinear motion, forming a complete argument about the kinds of elements. The work is both a key pillar of Aristotle's natural philosophy and the theoretical basis for the geocentric model of the cosmos that prevailed for nearly two thousand years, profoundly shaping Islamic philosophy, medieval scholasticism, and European thought down to the eve of the early modern scientific revolution. This edition presents the English text with a Chinese introduction and notes, helping readers grasp the terminology and the thread of argument while reading the original.