George P. Klubertanz's text proves that no realistic philosophy can be considered complete unless it includes a philosophy of nature. Most problems with the philosophy of nature occur within the area of human nature and its own philosophy, some of them in a crucial form. Moreover, the philosophy of human nature is an absolute prerequisite for a philosophically grounded ethics. Clearly, then, a knowledge of the philosophy of St. Thomas Aquinas requires a study of the philosophy of human nature.