Natural law theory offers numerous benefits as a source of ethical and legal norms. Father Joseph Koterski says that universality, objectivity, and intelligibility are three ideals for natural law theory.Footnote 1 Universality means that it is applicable to all persons at all times, in contrast to positive law which is location and time relative. It also implies, especially when combined with the ideal of intelligibility, that the natural law is knowable by all and that therefore all are responsible for keeping the natural law. A person is exempt from this responsibility only if she or he is not able to understand the natural law. This is not true of positive law, in that a person may be capable of knowing the positive law but not in the right location or time period to have access to that law. Natural law is very appealing because of its universality: such a law would provide universal human rights and values that in turn would provide the foundation for interaction between cultures. It would also provide a standard for determining if a given positive law is just. Without natural law it seems that law would become the rule of the powerful, or the majority, or some similarly arbitrary system. There is much to be said in favor of the idea of a natural law that makes such a study profitable.
Yet one major critique of natural law theory is that it does not provide universal standards but instead can be (and has been) used to prove any position. There have been in the history of thought multiple thinkers who have based their ethical theories on what they believed to be natural law, and these theories are logically contradictory. Opposing political parties have made reference to natural law in order to support opposing legislation. Thus while, in theory, natural law has many benefits, the critic can rightly point to a very disappointing history.
The purpose of this paper is to examine this critique and to consider whether it is realistic to believe that natural law theory can achieve the ideal of universality. In order to do this the paper will examine two thinkers who are central to natural law thinking, and who would be expected to have very similar conceptions of natural law, Aristotle and Aquinas. What will be seen is that these thinkers have important differences in their ethical theories, which at first appearance lends support to the critique mentioned above. However, upon examination, it will be discovered that this difference arises because of differences between these thinkers about human nature. This difference will be further traced to a difference in view about the origin of human nature. The paper will therefore argue that while the critic of natural law is accurate in pointing out a disappointing history, this does not indicate a necessary failing in natural law theory.
Natural law theory can achieve unity through first coming to a consensus on human nature and, before that, coming to a consensus on the origin of human nature (the eternal).Footnote 2 It is precisely because this has not been done that there are differences with respect to the content of natural law. These differences are only an indication of logically more basic differences with respect to views of the eternal. Thus the critique of natural law theory should provide an impetus to re-examine the relationship between theories of human nature and theories of the eternal, and to achieve consensus about what is eternal.
In studying natural law, one inevitably encounters Aristotle and Aquinas. These thinkers make important contributions to natural law thinking and since Aquinas builds on Aristotle one can find overlap in their theory. Consequently, one would expect that if natural law can provide a universal system, such a system would be found in Aristotle and Aquinas.
Frederick Copleston says of Aristotle's ethical theory that it is:
frankly teleological. He is concerned with action, not as being right in itself irrespective of every other consideration, but with action as conducive to man's good. What conduces to the attainment of his good or end will be a ‘right’ action on man's part: the action that is opposed to the attainment of his true good will be a ‘wrong’ action.Footnote 3
Aristotle is not usually thought of as a natural law thinker in a strict sense. Yet, as Copleston points out, Aristotelian ethics is goal oriented, and that goal is the human good which is based on human nature. Further, Aristotle is commonly considered to have made a seminal contribution to natural law thinking. For the purposes of this paper he will be classified as a natural law thinker because he bases his ethical theory on what he believes to be human nature. The fact that Aristotle bases his ethical theory on human nature, and Aquinas does the same, and yet they come out with different theories, appears to give credit to the critique of natural law mentioned above. Both Aristotle and Aquinas are trying to give a law that is based on what they believe to be human nature, and what they consider to be universal to all humans in contrast to the positive law of a specific country or city.
Yet these two thinkers differ in important ways: they have different views of the eternal, and therefore different views of the human good. This becomes important for natural law because the specifics of the law, the precepts for daily life applicable to concrete situations, are based on the human good. Thus, differences of opinion about the human good, even where they are small, can lead to exponentially larger and larger differences about the natural law. This paper asserts the following: (a) natural law is based on the human good; (b) the human good is based on human nature; (c) human nature is based on what is eternal; (d) differences in belief about what is eternal will lead necessarily to differences in belief about human nature, the human good, and natural law; (e) natural law presupposes that the eternal is knowable; (f) holding a person responsible for knowing and doing the natural law requires first holding them accountable for knowing what is eternal.
One's view of the natural law is based on one's view of human nature. Human nature is what all humans have in common at all times. The natural law must be universal because human nature is universal. If there is a natural law, it applies to all humans just because they are humans. The critique on which this paper is centered is best regarded as an epistemological critique: we cannot know human nature and this is evidenced by the long history of disputing; thus we are left with only positive law. A less powerful reading of the critique is the metaphysical claim that there is no human nature. For a variety of reasons, I shall set aside this metaphysical critique. This paper will therefore be concerned with the epistemological reading of the critique: natural law requires that human nature is knowable.
According to Aristotle, the goal of metaphysics is to come to know what is eternal, as opposed to that which is transitory or potential.Footnote 4 Aristotle analyzes change in terms of actuality and potentiality. Matter without form is pure potentiality. Matter is given form but not existence. This becomes relevant for morality and natural law when we ask what ought I to do? The assumption behind this question is that the answer might be different from what I in fact do. A contrast thus arises between how things are in terms of my actions and what my actions ought to be. This change involves changing from potentially being excellent to achieving excellence in actuality. “There must be, in the individual person, an intellective psuche that manifests an acquired hexis (or habitus, in the later scholastic tradition), which is the developed potentiality for knowing. Within the context of Aristotelian metaphysics, this premise seems to be relatively straightforward: in order for an agent to know or to understand, that agent must have a potentiality or dunamis for knowing/understanding.”Footnote 5
For Aristotle the question therefore becomes what is the actuality of human nature toward which those with potential human nature are moving?
Just as for a flute-player, a sculptor, or an artist, and in general, for all things that have a function or activity, the good and the “well” is thought to reside in the function, so would it seem to be for man, if he has a function … What then can this be? Life seems to be common even to plants, but we are seeking what is peculiar to man. Let us exclude, therefore, the life of nutrition and growth. Next there would be a life of perception, but it also seems to be common even to the horse, the ox, and every animal. There remains, then, an active life of the element that has a rational principle; … human good turn outs to be activity of soul in accordance with virtue, and if there are more than one virtue, in accordance with the best and most complete.Footnote 6
This illustrates two things: Aristotle's approach to ethics as being based on his view of human nature, and the general truth that human nature is that which is peculiar to humans.
For Aristotle there is thus change from potentiality to actuality. This is a change from potentially having the form of a particular kind of being, to actually having that form. From this Aristotle concludes that there is an eternal prime mover: “Obviously, therefore, the substance or form is actuality. According to this argument, then, it is obvious that actuality is prior in substantial being to potency; and as we have said, one actuality always precedes another in time right back to the actuality of the eternal prime mover.”Footnote 7 This eternal prime mover, the Unmoved Mover, is thus pure actuality without any potentiality; it is the source of change in other beings from potentiality to actuality. On some readings of Aristotle there are multiple unmoved movers, at least one for each celestial sphere. The unmoved mover of the outer sphere is still given pre-eminence because the movements of the lower sphere can be regarded as accidentally (though not essentially) moved in imitation of the perfection of the outmost sphere.
For Aristotle the Unmoved Mover is pure actuality and is the origin of change from potentiality to actuality. The Unmoved Mover is not itself made of matter, and seems to be intelligence. Sometimes the Unmoved Mover is thought of as starting motion in the way the first domino in a series begins the motion of the rest of the dominoes. This is not an accurate picture. The Unmoved Mover initiates motion through its actuality and perfection. All other beings having some potentiality remaining in them strive toward actuality. The actuality of the form of human nature is eternal, and causes change in those with potential human nature. Aristotle thus gives us his view of the eternal:
It is clear then from what has been said that there is a substance that is eternal and unmovable and separate from sensible things. It has been shown also that this substance cannot have any magnitude, but is without parts and indivisible (for it produces movement through infinite time, but nothing finite has infinite power; and, while every magnitude is either infinite or finite, it cannot, for the above reason, have finite magnitude, and it cannot have infinite magnitude because there is no infinite magnitude at all). But it has been shown that it is impassive and unalterable.Footnote 8
Aristotle's metaphysical view has been called dependent dualism because change is explained in terms of the potential striving to become like the actually perfect. He applies this same framework to human nature. Humans are potentially excellent, and ethics studies how humans can become actually excellent. For Aristotle excellence involves possessing certain virtues with the aim of being happy. The good life is where a person actually has the excellences of the human form that are potentially present. These excellences are found in the virtues of which Aristotle speaks throughout the bulk of the Nicomachean Ethics, and also in the contemplative life he mentions in the last book of the Nicomachean Ethics. These virtues revolve around the social life and what is necessary for flourishing as a social being. Therefore, a natural law based on the Aristotelian view would aim at giving prescriptions on how to live the virtuous life as understood by Aristotle. Aristotle's view can be summarized as follows: all is eternal (in that there is no creation ex nihilo) and yet only the Unmoved Mover is pure actuality; the rest of the cosmos strives to reach pure actuality from the state of potentiality; the good life for a human is to achieve excellence that is potentially present in human nature; achieving these excellences (or virtues) will lead to happiness.
Aquinas builds on the Aristotelian framework while making some important adjustments. He generally accepts the Aristotelian view of man as a social being, and the virtues as outlined by Aristotle. However, he has a very different view of God than did Aristotle. It is even questionable as to whether the term “God” should be applied to Aristotle's view of the eternal. This paper will continue to use the term “eternal” and distinguish Aristotle's view of the Unmoved Mover as the eternal (and the cosmos itself since for Aristotle there is no creation ex nihilo), and Aquinas's view of God as the eternal.
Aquinas introduces a distinction not present in Aristotle's metaphysics between “nature” and “grace.” Aquinas “opened the way for the discussion of what is usually called ‘nature and grace.’…[grace includes] God the Creator; heaven and heavenly things; the unseen and its influence on the earth; man's soul; unity [nature includes] The created; earth and earthly things; the visible and what nature and man do on earth; man's body; diversity.… Aquinas's view of nature and grace did not involve a complete discontinuity between the two, for he did have a concept of unity between them.”Footnote 9 Thus Aquinas can be said to have a two-tiered system: on the lower level is the natural man exemplified by Aristotle's conception of human nature; on the upper level is the man of grace who can know God as revealed in special revelation. The lower level includes all that can be known by reason, whereas the upper level includes all that requires grace to be known. This means that while Aquinas believed that Aristotle “got it right” on the level of nature, there is a higher level of grace of which Aristotle was ignorant.
Aristotle, says St. Thomas, was speaking of imperfect happiness such as is attainable in this life; but Aristotle, as I have already mentioned, says nothing in the Ethics of any other happiness. His ethic was an ethic of human conduct in this life, whereas St. Thomas has not proceeded far before he has brought in consideration of the perfect happiness attainable only in the next life, this happiness consisting principally in the vision of God.Footnote 10
It should not be thought, however, that Aquinas believes that Aristotle made a mistake, or that there are two kinds of truth that are about the same object and yet contradictory. Copleston does note some tension between Aquinas's Christianity and Aristotelianism, but the general framework is that the natural man can go so far with reason, (and Aristotle went about as far as possible), but one can only get the whole picture when grace is supplied. Aristotle's picture is therefore not wrong but only incomplete:
St. Thomas's Christian faith frequently impinges on or has some effect on his philosophy. For instance, convinced that man has a supernatural final end, and a supernatural final end alone, he was bound to envisage the term of man's intellectual ascent as the knowledge of God as He is in Himself, not as the knowledge of the metaphysician and astronomer; he was bound to place the final goal of man in the next life, not in this, thus transmuting the Aristotelian conception of beatitude; he was bound to recognize the insufficiency of the State for fulfilling the needs of the whole man; he was bound to acknowledge the subordination of State to Church in point of value and dignity; he was bound, not only to allow for divine sanctions in the moral life of man, but also to link up ethics with natural theology, and indeed to admit the insufficiency of the natural moral life in regard to the attainment of beatitude, since the latter is supernatural in character and cannot be attained by purely human means. Instances of this impinging of theology on philosophy could no doubt be multiplied; but what I want to draw attention to now is the latent tension on some points between St. Thomas's Christianity and his Aristotelianism.Footnote 11
Aquinas believes that the natural man could fulfil all the commands of the law, but the fallen man cannot fulfil all the Divine commandments without healing grace.Footnote 12
Because the law is grounded on reason, limits placed on reason will limit the natural man's ability to know and do the law. Hence it is significant that Aquinas believes the natural man cannot know, from reason, that matter is not eternal. Aquinas does not believe that reason can prove that the world was created (the implication is that Aristotle did the best he could). It is in special revelation that one discovers the doctrine of creation.
That God created the world freely, does not of itself show that He created it in time, that time had a beginning. As God is eternal, He might have created the world from eternity. That this had been shown to be an impossible supposition St. Thomas refused to allow. He believed that it can be philosophically proved that the world was created out of nothing, but he maintained that none of the philosophical proofs adduced to prove that this creation took place in time, that there is, ideally, a first assignable moment of time, were conclusive, differing on this point from St. Albert. On the other hand, St. Thomas maintained, against the Averroists, that it cannot be shown philosophically that the world cannot have begun in time, that creation in time is an impossibility. In other words, though well aware that the world was actually created in time and not from eternity, St. Thomas was convinced that this fact is known only through revelation, and that the philosopher cannot settle the question whether the world was created in time or from eternity.Footnote 13
Thus the Thomistic natural law will necessarily involve aspects that Aristotelian ethics do not, giving rise to the differences that the critic points out. There are also important differences between Aquinas's view of God and the Unmoved Mover: God is the creator and God is personally concerned with the creation. While Aristotle's Unmoved Mover is intelligence, and therefore in a sense personal, there is no way for a human to have a relationship with the Unmoved Mover as can be had with God.
Is the God of Aristotle a Personal God? Aristotle sometimes speaks of God as the First Unmoved Mover … Aristotle may not have spoken of the First Mover as being personal, and certainly the ascription of anthropomorphic personality would be very far indeed from his thoughts, but since the First Mover is Intelligence or Thought, it follows that He is personal in the philosophic sense … if Aristotle's God is entirely self-centered, as I believe Him to have been, then it would be out of the question for men to attempt personal intercourse with him … For (a) God could not return our love, and (b) we could not in any case be said to love God.Footnote 14
Thus the Unmoved Mover and God are vastly different. While the Unmoved Mover is said to be the first mover, this first is not be understood as acting temporally, since Aristotle says that motion is necessarily eternal. Further, the Unmoved Mover is not the creator of matter, which according to Aristotle has existed from eternity (as has the cosmos as a whole).Footnote 15
With the addition of grace and scripture comes the further end of the beatific vision. Recall the passage quoted earlier in which Aristotle speaks about the end of human nature. Human nature does not, nor could it in view of his worldview, include this supernatural end. Yet also recall that Aristotle's ethics is based on human nature and the end of human nature. This means that Aristotle's ethics will be different from that given by Aquinas. Aquinas adds grace and special revelation: It is through special revelation that truths about the immortality of the soul, and the higher goal of knowing God, are revealed. According to Aquinas, a full understanding of natural law requires a knowledge of this higher goal of knowing God. Some of the precepts of natural law will be aimed at this end and therefore will differ from precepts based purely on Aristotle's metaphysics.
Aquinas's position can be summarized as follows: Only God is eternal (everything else was created by God ex nihilo); humans can know that God is creator and personal, but they cannot know that God created matter ex nihilo apart from special revelation; there is a lower level of the good life available to all through general revelation (natural philosophy); the best life is available only through special revelation. Consider this general statement by Aquinas:
It is therefore evident that as regards the common principles, whether of speculative or of practical reason, truth or rectitude is the same for all, and is equally known by all. As to the proper conclusions of the speculative reason, the truth is the same for all, but is not equally known to all; thus it is true for all that the three angles of a triangle are together equal to two right angles, although it is not known to all. But as to the proper conclusions of the practical reason, neither is the truth or rectitude the same for all, nor, where it is the same, is it equally known by all. Thus it is right and true for all to act according to reason.Footnote 16
This demonstrates the general reality that if truth is the same for all then if God is the Creator this is true for all. Speculative reason requires that people believe this (assuming it is true) as opposed to believing that there is no creator. Therefore, for Aquinas speculative reason requires that we believe in God the Creator, and for Aristotle speculative reason requires that we believe there is no Creator. For a more concrete example consider the following:
As Augustine says (De Lib. Arb. I,5), ‘that which is not just seems to be no law at all’; therefore the force of a law depends on the extent of its justice. Now in human affairs a thing is said to be just from being right according to the rule of reason. But the first rule of reason is the law of nature, as is clear from what has been stated above (Q. XCI, A. 2, Reply 2). Consequently every human law has just so much of the character of law as it is derived from the law of nature. But if in any point it differs from the law of nature, it is no longer a law but a corruption of law.Footnote 17
Human laws should be framed in a general rather than a particular way:
Whatever is for an end should be proportionate to that end. Now the end of law is the common good; because, as Isidore says (Etym. V, 21) ‘law should be framed not for any private benefit, but for the common good of all the citizens.’ Hence human laws should be proportionate to the common good. Now the common good comprises many things, as to persons, as to matters, and as to times. Because the community of the state is composed of many persons, and its good is procured by many actions; nor is it established to endure for only a short time, but to last for all time by the citizens succeeding one another, as Augustine says.Footnote 18
Hence any particular law must be based on natural law, which is based on human nature and the eternal. Aquinas denies that a person can lead the good life without knowing God and receiving the grace of God, although the natural man can have some good proportionate to his nature:
Human nature needs the help of God as First Mover, to do or will any good whatsoever, as stated above (A. I). But in the state of integrity of nature, as regards the sufficiency of the operative power, man by his natural endowments could will and do the good proportionate to his nature, such as the good of acquired virtue, but not surpassing good, as the good of infused virtue.Footnote 19
Both Aristotle and Aquinas would agree that we should act in order to achieve the good and that the good is based on human nature, and yet they arrive at very different views of how we should act. The problem for natural law theory is that these two systems will end up producing natural laws with different content. Even though these two thinkers are very similar their differences with respect to the nature of the eternal are enough to make for very different views of the human good. Now that the differences between Aristotle and Aquinas have been examined, a resolution can be sought to the problem that natural law can apparently be used to support almost any ethical position.
The claim made above is that natural law is based on the human good, the human good is based on human nature, and human nature is based on the eternal. Differences at the level of natural law are indications of differences at the more basic levels. Aristotle believes that the cosmos is eternal while Aquinas believes that God created the cosmos. If a person achieves excellence in philosophy which one are they to believe? Further, in Aquinas's worldview God is personal. For Aquinas the good life includes having a personal relationship with God, and yet there is nothing like this for Aristotle. The differences between these thinkers about the nature of the cosmos and what is eternal result in important differences in their theory of natural law. It therefore seems to be theoretically possible to arrive at a universal natural law only by coming to consensus on the nature of the eternal.
A consensus about the nature of the eternal presupposes that the eternal is knowable. If the eternal is not knowable then neither is human nature, the human good, or natural law. Natural law theory presupposes that the metaphysical foundation of the natural law is knowable. Metaphysics is unpopular today. However, the fact that some metaphysical systems are incoherent does not mean that all metaphysics should be avoided. And it seems that there is a need for some knowledge at the metaphysical level to make sense of a natural law theory. The eternal must be knowable if there is to be a natural law. It is thus necessary first to establish what is eternal and then to move on to determine the nature law based on the eternal. This can be called a “presuppositional approach”: the more basic truths must be established before the less basic issues are dealt with.
A central difference between Aristotle and Aquinas about the eternal is whether matter is created or not. Aquinas appeals to special revelation in order to settle this question, which is unhelpful in coming to consensus because (a) Aristotle did not have access to this special revelation, and (b) not everyone agrees as to whether there is special revelation and as to just what counts as special revelation. Therefore, staying within the realm of reason, which is accessible to all, I suggest a way of achieving consensus on this issue through presuppositional thinking:
Aristotle believed that matter is eternal (although dependent), and Aquinas believed that this could not be disproved through reason. “The First Mover is not a Creator-God: the world existed from all eternity without having been created from all eternity. God forms the world, but did not create it, and He forms the world, is the source of motion, by drawing it, i.e. by acting as final cause.Footnote 20 Aristotle believes that matter is eternal because: “neither the matter nor the form comes to be-and I mean the last matter and form. For everything that changes is something and is changed by something and into something. … Note, next, that each substance comes into being out of something that shares its name.”Footnote 21 For Aristotle creation ex nihilo is not possible. He correctly asserts that “nothing” cannot cause something to exist, however he does not seem to consider the possibility of God causing matter to exist from or of nothing (this is not an uncaused event because God is the cause). But this raises a dilemma for Aristotle: either matter has some actuality without the Unmoved Mover and is then not dependent or matter has no actuality without the Unmoved Mover and then is brought into being by the Unmoved Mover. Aristotle cannot accept the first option because he himself argues that matter cannot be independent of the Unmoved Mover. Matter without form is, according to Aristotle, pure potentiality; but if matter has some actuality apart from the Unmoved Mover then it is not pure potentiality anymore. However, the second option implies that, while matter exists eternally in the mind of the Unmoved Mover, it only actually exists through a creative act. If reason apart from revelation can demonstrate this then Aquinas gave up too soon on the ability of reason.
Aquinas himself argues for the existence of God by asserting that there is no composition of the existence and essence of God, that for God these are the same. If they were not, “if there were composition of essence and existence, for instance, God would owe His existence to another being, which is impossible, since God is the first Cause.”Footnote 22 This implies that only God is eternal, and all else owes its existence to God. Further, this is shown through reason.
That reason can demonstrate that matter is not eternal can be further seen in Aquinas's consideration of time. The problem that Aquinas says cannot be solved by reason is the following: did God create the world from eternity or in time; the solution given by reason (as opposed to special revelation) is that God created the world and time itself. Aquinas affirms that time is the measurement of change, or motion, in terms of before and after. Thus if there were no object that is in motion there would be no time. Further, Aquinas affirms that for God, who is eternal, there is no time. Consequently matter is dependent on God for its existence, and the act of creation is the act that brings time into existence through bringing changing beings into existence. Time is not eternal, but rather had a beginning. Consequently, it can be shown by reason that matter is not eternal.
This argument is valid if one first assumes that there is a substantial difference between God and the created order. Aristotle does not make this assumption but instead believes that all is eternal and explains difference and change by the process of potentiality and actuality. The dilemma for Aristotle is the following: either matter has some actuality apart from the Unmoved Mover or it does not. If matter has some actuality apart from the Unmoved Mover then its existence is independent. Aristotle cannot maintain this because he argues against this position as held by some Pre-Socrates. Yet if matter is absolutely dependent on the Unmoved Mover then it does not exist independently and this is the same as the relationship between God and the creation (matter without form is pure potentiality until it is given form and therefore actuality by God the Creator). None of this relies on special revelation and could have been thought through by Aristotle. This at least indicates the possibility of knowing God the Creator through general revelation and therefore undermines the idea that Aristotle exemplifies the natural philosopher.
This consideration of the creation of matter is meant to illustrate that it is possible to discern through reason the nature of the eternal. Consensus can be achieved about the eternal, and this implies that consensus can also be achieved about human nature, the human good, and the natural law. One need not appeal to special revelation in order to argue that the world was created and is not eternal. There can certainly be questions raised about this issue, but the intention has been to show that Aristotle and Aquinas did not exhaust the possibilities of reason; instead, it seems that they did not use reason enough and missed the alternative that matter is dependent and created, as is time itself.
Having first established that it is necessary to know the eternal in order to establish a universal moral law it can then be asked whether all or only some need to be able to know the eternal. Responsibility is relative to how much a person can know: if a person cannot know the law, then she or he cannot be held responsible for obeying or disobeying the law. Since knowing the natural law requires first knowing what is eternal then holding persons accountable for knowing the natural law requires also holding them accountable for knowing the eternal. If the eternal is not knowable by all then a universal natural law is not achievable. Knowing the eternal is therefore a necessary condition for knowing the human good and natural law, although it may not be sufficient (more is needed).
Humans are responsible because they have the ability to know the natural law. This introduces a further level of responsibility in that humans have the ability to know the eternal. Humans are therefore responsible for knowing the natural law, and that presupposes that they are also responsible for knowing the eternal. Knowing the eternal is a necessary condition for knowing the good so that if we hold people responsible for knowing what is good, we must also hold them accountable for knowing the eternal. Thus the first level of responsibility for a human is knowing what is eternal. The differences in worldviews and the various systems of law that these produce are a result of differences in views about what is eternal, and humans can be held responsible for dealing with these differences through the use of reason.
The criticism this paper has addressed is: natural law theorizing is not helpful because natural law has been used to support contrary positions on just about every issue. This criticism has a basis in historical truth. However, the question is whether this is a necessary quality of natural law theory or whether it can be overcome. This paper has argued that it indeed can be overcome. The differences in systems of natural law have been traced to differences in views about the eternal. Even two thinkers as close as Aristotle and Aquinas have differences that affect their theories of law. Therefore, if a universal natural law is to be presented, one that is unified and can offer helpful insights and solutions to the issues facing humanity today, then there must be a consensus on what is eternal. As long as there are differences of view about the eternal there is no hope of a universal natural law. An implication of this solution is that humans are responsible to know what is eternal. All responsibility with respect to the natural law presupposes that humans are responsible for knowing what is eternal. It is therefore not only theoretically possible to have a consensus on what is eternal, but humans have a responsibility to acquire this knowledge.
This solution makes possible a central value in natural law theory: universality. Natural law theory asserts that the law is based on human nature, and there is only one human nature. Therefore, there is only one natural law. The emphasis in natural law theorizing must be on obtaining a correct view of human nature on which a natural law can be based. Because one's view of human nature depends on one's view of the origin of human nature, a correct view of human nature will first require having a correct view of the eternal. The critique of natural law considered in this paper should inspire a rethinking of the differences currently widespread about what is eternal, and encourage natural law thinkers to work toward a consensus about what is eternal, human nature, and the human good, in order to lay the foundation for a natural law.
