Since then, a tradition of scholarship has developed which is called Thomism , alongside a particular criteria for determining if any philosophical doctrine may be received under its banner and whether its professor may be considered an orthodox Thomist. And because popular reading understands St. Thomas as having integrated Aristotle's philosophy into his thought , the tradition is also understood to be Aristotelian-Thomistic.
In the context of the tradition, the new classicists, John Finnis, Germain Grisez and Joseph Boyle, have been subject to such criticism for their interpretation of St. Thomas that they have denied any association with that tradition. In Practical Principles, Moral Truth, and Ultimate ends, under a heading Please Note Well, they declare,
- "While this paper proposes philosophical clarifications and arguments rather than textual interpretations, it uses some language common in the (broadly speaking, Thomistic) natural-law tradition from which we developed that theory. But what we say here differs in various ways from the theories articulated by Aristotle, Thomas Aquinas and others." 
My aim here is not to argue against that declaration nor to vindicate their orthodoxy. Instead, I hope to show that Thomists can embrace the new classicists' thesis that the many first principles of natural law are self evident without committing the breach of tradition, confining ourselves only to the problematic of natural law relevant to this very thesis as such. The primary charge against the new classical reading, amongst other things, is that it denies that ethical principles are founded on human nature. Henry B. Veatch, one of the new classicists' most vehement critics , complains,
- "True, there is a sense in which our human moral obligations can scarcely be said to be "inferrable" from a knowledge of human nature. And yet Finnis is surely going too far when he would apparently conclude from this that "the norms referred to in any theory of natural law" are not to be regard as being even "based upon judgments about nature (human and/or otherwise)" (NLNR, 1980. p. 35)". 
But it will not be too difficult (but with our help, nevertheless) to point out that Finnis never concluded what Veatch accuses him of concluding. The phrase `based upon judgements about nature' is stylistically ambiguous and Veatch capitalizes on that for his equivocation. `Based upon judgments about nature' can mean `inferred from judgments about nature' or `having an ontological connection with judgments about nature. While Finnis means the former, which renders Veatch's statement a silly, uninformative tautology, Veatch makes him out as concluding the latter.
Finnis' reply is embarrassing. With "an invitation to Professor Veatch.to read what we [Finnis and Grisez] have written", the apology goes:
- "Henry Veatch's "sharp questions" are directed to those who deny that morals and ethics have any basis in nature or the facts of nature;.to those who "insist that ethical principles can have no grounding in fact and nature"; to those who suppose an "absolute independence of ethics as over against metaphysics, or of moral with respect to a knowledge of nature," so that "principles of morals and ethics are really not to be thought [of] as being in any sense principles of being or of nature at all".Veatch's questions and objections, therefore, are not properly directed to either Germain Grisez or to myself. Neither Grisez nor I subscribe to any of the foregoing denials, affirmations, and suppositions; indeed, we reject them all. Neither of us has published anything which might reasonably be interpreted, in its context, as involving or entailing any such view." 
Veatch is not alone, of course. Lesser known Anthony J. Lisska has his own "worries": Can one have an Aristotelian meta-ethical theory without a consistent metaphysics of human nature?  Is Finnis correct in suggesting that the role of human nature is not a necessary condition for natural law ethics?  Then, rebuking what he supposes is Finnis' position, he quotes two noted Thomists to justify his position against Finnis:
- "In his The Tradition of Natural Law, Yves Simon suggested that a
theory of universals, or essences, is a necessary condition for an
elucidation of the concept of natural law:
Let us confess that it is meaningless to argue seriously about natural law without having ever raised the question of universals.It is obvious that the theory of natural law opposed by the nominalist tendency and probably would be impossible by a strictly and consistently nominalistic philosophy, if such could exist.
In Man and the State, Maritain argues explicitly for the concept of essence as a necessary condition for understanding Aquinas on natural law. He writes:
What I am emphasizing is the first basic element to be recognized in natural law, namely the ontological element; I mean the normality of functioning which is grounded in the essence of that being: man.Let us say, then, that in its ontological aspect, natural law is an ideal order relating to human action, a divide between the suitable and the unsuitable, the proper and the improper, which depends on human nature or essence and the unchangeable necessities rooted in it." 
Precisely. The irony of it all is that these auctoritates really support rather than contradict the new classical reading. The point that Yves Simon and Maritain is making is that the principles of natural law presupposes a human nature or essence. This is an ontological point. We are talking about what is the case, objectively, from a third-person-point-of-view. To talk about principles of natural law is to talk about a set of objective ethical principles which are somehow fixed. If they are fixed, then it implies there must necessarily be an essence in man, a stable "what-ness" in man, so that it may give rise to this fixed set of ethical principles called natural law. At the metaphysical or ontological level then, the Aristotelian-Thomistic natural law theorist is always implicitly committed to essentialism.  Thus Simon rejects a natural law with a nominalistic, non-essential ontology and Maritain talks about natural law depending on "human nature or essence and the unchangeable necessities rooted in it".
But the new classicists do not deny this. Compared with the above ontological point, theirs is epistemological point, namely, that our knowledge of the principles of natural law does not pressuppose our knowledge of the human nature or essence. This is perfectly consistent with the ontological point in the preceding paragraph which Simon and Maritain made. As a matter of fact, the ontological point is implied because as was said above, to assert such a thing fixed as natural law in man is to assert something essential in man.
To see the implication, let us use an example. Suppose I walk into the room, and starring at the floor I see some tiles. Now, if I were to smash the tiles up, I would see beneath them the concrete ground. Now, epistemologically, the tiles were prior as differ from the concrete grounds. But the concrete floor was beneath the tiles, supporting the tiles. And so ontologically, or "in the order of generation" as the scholastics are wont to say, the concrete ground was prior as differ from the tiles. Without the concrete ground being there first, the tiles could never be in place. Indeed, the existence of the tiles is determined by the existence of the concrete ground. Yet I see the tiles first before I actually discover the concrete ground underneath them.  Another example is to consider the eye and its seeing. For the eye, the light and data that enters the eye has epistemic priority, yet were it not first that the eye had a retina, it could never see. Infact the eye will never see its own retina, so that the retina is forever epistemically last, yet it is there ontologically prior to everything it sees, i.e., to the light which enters the eye, which, as is obvious, is epistemically prior as contrast with the retina.
So it is with the case of human nature/essence and the principles of natural law. While the principles of natural law have epistemic priority, human nature/essence has ontological or metaphysical priority. Robert P. George puts it very well:
- "Knowledge that comes as the fruit of practical reflection becomes
available to (i.e., provide data for) speculative inquiry (e.g., in
metaphysics or theology). On the basis of one's practical grasp of
the intelligible ends of human acts, one may derive propositions
about the nature of human beings. The point is that in the
epistemological mode of inquiry, our (practical) knowledge of
human good(s) is methodologically prior to our (speculative)
knowledge of human nature. The latter knowledge presupposes the
former: It is not, as neo-scholastics suppose, the other way round.
Let us shift for a moment to the ontological mode. Here, if we reflect on Aquinas's methodological principle, it is clear that the human goods are goods for (i.e., fulfillments of) human beings precisely because human beings have a nature as they do. As Finnis says, "[t]he basic forms of good grasped by practical understanding are what is good for human beings with the nature they have." Were human nature otherwise, human goods would be correspondingly different. In this sense, the basic goods depend, ontologically, upon human nature. So in the ontological mode of inquiry, an account of the human goods will refer to human nature: "Why are these the ends fulfilling of human beings?" "Because human nature is constituted as it is." But this answer in no way entails that our knowledge of the ends as human fulfillment is derived from prior speculative knowledge of human nature." 
The case is clear, and the verdict certain. The new classical reading must be said to be consistent with the Aristotelian-Thomistic tradition. Within the limits of the analysis, it seems to me that Thomists who embrace the new classical reading cannot be chided for straying from the narrow path of orthodoxy.
 Leo XIII, "Aeterni Patris: The Study of Scholastic Philosophy", in The Great Encyclicals Letters of Pope Leo XIII, 1995: TAN Books and Publishing, (USA). p. 48
 Whether there is such a thing as Thomism is itself a matter of debate among scholars. Some argue that there is no such thing, that St. Thomas himself was not a Thomist, and that to aspire to Thomisms or such like is a betrayal of the spirit of the Angelic Doctor. Nevertheless, let that not bother us. The common opinion is that there is a Thomism.
 Of course, as Alasdair MacIntyre has argued, St. Thomas integrated both Platonism (under the guise of St. Augustine) and Aristotelianism into his thought. See his After Virtue. 6th ed. 1996: Duckworth (UK) St. Thomas is popularly associated with Aristotle because he was the first to seriously integrate Aristotle, as compared to his contemporaries who stuck with St. Augustine only. Hence compared with them, St. Thomas was very much more Aristotelian. Yet a proper reading of St. Thomas based on the last 40 years of research suggests that his philosophical insights might also have a (Neo-) Platonic as well as an Aristotelian base. See John. D. Caputo, Heidegger and Aquinas: An Essay on Overcoming Metaphysics, op. cit., pp 125-8. Also, Kevin Corrigan's article in The Thomist, "A Philosophical Precursor to the Theory of Essence and Existence in St. Thomas Aquinas" where the real distinction of St. Thomas is linked to the Enneads of Plotinus., p. 219-240.
 Germain Grisez, Joseph Boyle, and John Finnis, "Practical Principles, Moral Truth, and Ultimate Ends in Natural Law" in Natural Law: Volume I. (ed.) John Finnis. 1991: Dartmouth (UK), p. 237.
 See also Russell Hittinger, A Critique of the New Natural Law Theory, 1987: Univ. Notre Dame Press (USA) which argues that the new classicists fail to "interrelate systematically practical reason with a philosophy of nature" (p.8). Also see Robert P. George's reply in "Recent Criticism of Natural Law Theory" in University of Chicago Law Review, (55), 1988. Includes a reply also to Lloyd L. Weinreb's Natural Law and Justice, which criticizes the new classicists on this and other counts.
 Henry Veatch, "Natural Law and the 'Is' - 'Ought' Question: Queries to Finnis and Grisez" in Swimming Against the Current in Contemporary Philosophy, 1990: Catholic University of America Press. (USA). p. 300. Footnoted to this very same quote is the following: "Be it noted that Finnis and Grisez would not argue that ethics is independent of metaphysics merely in the way which, say, physics is independent of metaphysics. For in addition, ethics is to be distinguished from metaphysics, they would say, in the way in which a practical science is different from, and hence independent of, any theoretical science…" So by "independent of" Veatch means something more than just mere differentiation.
 John Finnis, "Natural Law and the 'Is' - 'Ought' Question: An Invitation to Professor Veatch" in Catholic Lawyer, (26) 1981, p. 266.
 Anthony J. Lisska, Aquinas' Theory of Natural Law, op. cit., p. 140.
 Ibid., p. 148
 Ibid., p. 149-50
 I owe this insight to Dr. Alan Brown.
 This example is adapted from Fritz Wenisch's "A Defense of Dietrich von Hildebrand's Approach to Ethics" in ALETHIEA, (5): Truth and Value, 1992.
 Robert P. George, "Recent Criticism of Natural Law Theory" in University of Chicago Law Review, (55), 1988, p. 1416.