4. There is, therefore, only one science of human conduct which is authentic, complete, and capable of existing as such in gradu scientiae practicae: it is that one which takes into account at once the essence and the state, the order of nature and the order of grace. All the great ethical systems which are ignorant of the ways of grace, however rich in partial truths they may be, are bound to be deficient.

What in the light of all this are we to think of Aristotle's ethics, which St. Thomas commented upon? It too is deficient. It is, if you wish, the closest approach to what the aforesaid practical science of human conduct in a state of pure nature would be; still it is certainly not that science any more than the rest. We should say rather that its outstanding value lies in its wealth of practical truths which stem from the sole consideration of human nature. And that is why it presents us with a great number of insights and principles from natural ethics in the sense I have defined it, that is, an abstractly isolated part of ethics purely and simply so-called, or again, practical philosophy inadequately considered. It is from this standpoint that St. Thomas commented on it. However, we gather from these remarks that his commentaries ought not to be used without discretion, and that this is not always a simple matter. For St. Thomas, steadfast in his clearly defined role of commentator, rigorously restricts himself to the literal interpretation of Aristotle's text; but true at the same time to the claims of moral science he integrates this literal explanation as far as possible -- explicitly or implicitly as occasion demands -- with the complete system of moral science. In view of this restriction to the letter of Aristotle, we should err in taking these commentaries on the Ethics and the Politics for a Christian moral system, or for a finished and adequate formulation of moral science (they are rather a proximate preparation therefor). And in view of the bent of the interpretations furnished, it would be equally erroneous to see in them a simple exegesis of Aristotelian ethics (they are an exegesis of Aristotle, but in a higher perspective).