The chapter surveys the contributions of Aristotle to the development of ancient Greek science. Aristotle sought the stable element and reliable truth within changes. Aristotle develops a three-fold system of scientific disciplines: practical, productive, and theoretic (including mathematics and natural philosophy). The primary natural kinds are the four elements, earth, water, air, and fire, composed of the fundamental qualities of hot/cold and wet/dry. Each has a natural place, earth in a sphere at the center of the cosmos, and the others in spherical shells around that. The eternal circular heavenly motions are due to the fifth element, “aithēr.” Aristotle’s scala naturae classifies all life: plants are capable of nutrition and reproduction, animals can also perceive and move, and humans can reason. Aristotle also studied the transformation of substances, but mainly focusses on the generation, the parts, and the functions of animals. Aristotle’s chief explanatory tool is the “final” cause, the purpose for which a thing occurs.