A systematic investigation of how substances come into being and pass away, analyzing the principles and causes of substantial change. It argues that generation and corruption arise from the interplay of form and matter—where a thing acquires a new form as the privation of the old—and treats change as the actualization of potentiality through contraries, especially illustrated in transformations among the four elements (earth, water, air, fire) whose differing qualities explain natural motion and alteration. The work distinguishes true substantial change from mere qualitative or accidental alteration, examines mixtures and separations, and insists on causal explanations (material, formal, efficient, and final) to account for natural processes such as growth, decay, and elemental transmutation.