From St. Augustine, The City of God, book 11, chapter 25 (trans. Dyson):
. . . the philosophers have wished to divide their discipline into three parts (or, rather, were enabled to see that there is such a threefold division; for they did not invent it, but only discovered it): of which one part is called physical, another logical and the third ethical. . . .
. . . . Plato, however, is said to have been the first to discover and recommend this division, and he saw that only God could be the author of nature, the giver of intelligence and the inspirer of the love by which life is made good and blessed. Also, it is certain that, though opinions differ as to the nature of things, and the method of investigating truth, and the good to which we ough to refer all that we do, it is to these three great and general questions that all the efforts of the philosophers are devoted. Thus, though there is much disagreement as to which view each man ought to take in respect of any of these questions, no one doubts that nature has some cause, science some method, and life some purpose.