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Natural Law is reason

For us, human beings, our intelligence is our natural law

When God created us, God made us in his own image. This means that, like God himself, we have the ability to think, to work things out in our mind and re-create our world – to some extent – to suit our specific needs. While depending on the biology of our bodies and the physical world in which we live, they re-shape those realities through our intelligence.

But if our distinctive feature as human beings is that we possess the faculty of reason, it has consequences for ethics. In us, Natural Law, the basic law of good and evil is centered on our mind. Human morality consists in our mind judging what is good and what is evil  after considering all the elements of our complex human situations.

This line of thinking was already recognised by Thomas Aquinas in the 13th century. It has since been developed by Neo-Thomists and others in a number of parallel approaches. In our own time the approach through reason is the interpretation followed by the majority of Catholic theologians.

We offer here a representative selection of texts.

St Albert the Great
St Albert the Great

“It has to be said that natural law, which is stated to be the law of our mind, is an inborn ability as far as universal principles are concerned that lay down rules for the good. For this is the light spoken of in Psalm 4,7: “The light of your face is sealed upon us, o Lord”. Therefore the law of our mind is an inborn ability with regard to principles, but an acquired ability with regard to [specific] matters we discern .
This can be deduced from Basil who says that natural law is inscribed on our natural tribunal. But that tribunal is our [human] reason. Natural law is inscribed on our conscience, because through it [i.e. through natural law] it always drives to what is good.”

Albert the Great (1193-1280),


St Thomas Aquinas
St Thomas Aquinas

“The rational creature is subject to  Divine providence in the most excellent way, in so far as it partakes of a share of  providence, by being provident both for itself and for others. Wherefore it has a share of the  Eternal  Reason, whereby it has a  natural inclination to its proper act and end: and this participation of the  eternal  law in the rational creature is called the  natural law. The practical reason [= the mind thinking about action] is busied with contingent [= specific and transient] matters, about which  human actions are concerned: and consequently, although there is  necessity in the general principles, the more we descend to matters of detail, the more frequently we encounter deviations . . . Thus it is right and  true for all to act according to reason.
Consequently we must say that the  natural law, as to general principles, is the same for all, both as to rectitude and as to  knowledge. But as to certain matters of detail, which are conclusions, as it were, of those general principles, it deviates.”

Thomas Aquinas (1225-1274), Summa Theologicae I-II qu. 90-91


Fr Samuel Ryan
Fr Columba Ryan

“To discover what it is to be human and to achieve properly human fulfilment, account must be taken of the human being not simply as a biological object, not even simply biologically (which would introduce a whole consideration of his ecology), but in the specifically human dimension in which he/she enters into communication with others at a human level . . .
Upon the primary recognition of Natural Law {“Do good, avoid evil”) one cannot immediately base principles such as “Thou shalt not commit suicide”, “Thou shalt not practice birth control”, “Thou shalt not lie”, and so on, but rather upon principles of the form “some arrangements should be made for the preservation of life”, “some for the organization of the family”, “some for the organization of society”, in each case leaving it open to further experience and enquiry what the arrangements are to be . . . The natural law has different levels. Basically it consists of those highest principles which are simply given and indemonstrable – whether as the rules of moral conduct or as the primary axioms of an entirely general moral awareness. But it comprises also anything which reason may derive by way of conclusion, from such axioms, and which may serve in turn as principles in reaching individual decisions as to conduct.”

Columba Ryan (1234), The Traditional Concept of Natural Law: An Interpretation, In Illud Evans (ed.), Light on Natural Law, London 1965, p. 13 – 37.


Fr Bernard Häring
Fr Bernard Häring

“The fundamental principles of the natural law can be known with certainty by every normal man in possession of his reason. They are in fact self-evident. Following is the most universal principle of the natural law: the known good must be done (bonum est faciendum: Thomas); the good must be loved (de bono est complacendum: Scotus). . . .
As such, the moral law of nature is immutably valid. But its application is variable according to the changeableness of conditions . . . Today we see clearly that the eternally valid propositions of natural right also include the duty of acting in accord with historic exigencies and situations. Human beings must act rightly in the historic context, though it cannot be rigidly and statistically determined for all times what is historically correct and right. Only the knowledge of the immutably valid essential laws of natural right [on the one hand] and of the historic situation [on the other] makes it possible [for human reason] to form a judgment in every individual instance as to what is “historically right” and therefore also, in the full sense, “right according to nature.”

Bernard Häring, The Law of Christ, Cork 1961, pp 238-250.


Fr John MacQuarrie
Fr John MacQuarrie

“Man, in his freedom and responsibility, has a share of creativity and cooperates with God in the shaping of the world. More and more, man takes over the direction of “nature”—both external nature and his own nature, that is to say, those elements of his being that are simply “given.” As this process goes on, it is clear that “natural law,” in the sense explained above, must have flexibility. What might have been against natural law at one time may not still be against it as man, fulfilling his destiny, reshapes his own “nature” or develops it or reduces the area of the “given” by bringing more of his being under his conscious responsible will. One obvious controversial example of these matters is the question of contraception or birth control. On the one hand, man has, by better health arrangements, extended his life-span and his chances of survival far beyond what was once “natural,” that is to say, simply given. No one condemns this. On the other hand, then, surely it is equally in order to take over from nature control of procreation, and to achieve in a responsible way by suitable techniques that balance between new life and death which was once regulated by the merely “given” factors in both man and his environment, for some such regulation is required if we are to have regard to the quality of existence and not just to the biological (and probably miserable) proliferation of life.”

John Macquarrie, Christianity and Ethics, London 1966, pp 503-512.


Fr Charles Curran
Fr Charles Curran

“The encyclical on the regulation of birth employs a natural law methodology which tends to identify the moral action with the physical and biological structure of the act. The moral conclusion of the encyclical forbidding any interference with the conjugal act is based on “the intimate structure of the conjugal act” (Humanae Vitae n. 12). The “design of God” is written into the very nature of the conjugal act; the person is merely “the minister of the design established by the Creator” (Humanae Vitae n. 13).  . . .The concept of natural law employed in traditional ethics tends to define the moral act merely in terms of the physical structure of the act. In contemporary theology such an understanding of natural law has been severely criticized. Newer philosophical approaches have been accepted by many Catholic thinkers.”

Charles Curran, Theologians and Humanae Vitae, Sheed & Ward, New York, 1969, pp 156-172.


Fr John McCabe
Fr Herbert McCabe

“Now, the question arises: how are we to identify those acts which are not merely inadequacies in living the life of love but actually incompatible with the love upon which human community depends? It is a mistake to think that we find the answer to this by looking at a list of wrongdoings and arranging them in order of “gravity”. St Thomas’s answer is: by the use of our practical reasoning and also by faith in divine revelation; and the deliveries of these two sometimes overlap. In its primary meaning, for him, “natural law” just is our capacity for practical reasoning; reasoning, that is, about what to do, based on the principle “seek good and avoid evil”,
just as theoretical reasoning about what to think is based on the principle “seek truth, do not contradict yourself’.”

Herbert McCabe OP, Veritatis Splendor in focus, The Tablet, 18th December 1993.


Fr Gerard J. Hughes
Fr Gerard J. Hughes

“As will be seen, then, Aquinas’s view of natural law combines
the conviction that what one ought to do is based upon what is good for human beings given how human nature functions, with a remarkably flexible account of what people ought to do in practice. Consistency requires that we treat similar situations in the same way, and the injunction that we should do good and avoid evil requires that in explaining our choices we have to be able to explain the good at which we were aiming. But neither these requirements, nor any of the
more specific statements about what things are good for human beings, will of themselves settle how particular decisions have to be taken.”

Gerard J.Hughes SJ, Natural Law Christian Ethics, An Introduction, ed. by Bernard Hoose, Cassell 1998, ch. 2.


Jean Porter
Jean Porter

“Given its stance on the goodness of procreation we would expect the Christian community to discourage the use of contraceptives. We as a community cannot celebrate human procreation as a centrally important way of expressing our faith in the goodness of God’s creation without also implying that the deliberate frustration of human fertility is at best regrettable. It does not follow however that the use of contraceptives is never morally justified. Nor does it imply that the Christian community should attempt to formulate the circumstances in which contraceptives may or may not be used; this is the sort of judgment that can best be made by particular couples, in view of their own circumstances and personal needs.”

Jean Porter, Natural and Divine Law, Novalis 1999, pp 224-234.


Fr Adrian Hastings
Fr Adrian Hastings

“The root idea of natural law is that we, being rational, are also inherently moral beings, and that the exercise of moral judgement reflects what God has made us, and necessarily opens to us an awareness of divine law, whether or not we recognize it as such. In its primary principles, natural law is absolutely immutable, but not so in its secondary principles. That is to say, people can reasonably conclude in regard to some particulars that what is good or bad in one cultural condition is otherwise in another. Aquinas explicitly agrees that natural law can change in certain particulars (ST I-II q. 95 a. 5). Thus polygamy could be against natural law in one society but acceptable to it elsewhere. In conditions of high infant mortality such as long prevailed almost everywhere, contraception could be morally unacceptable, but, in conditions of low infant mortality and high population increase, the opposite might be the case.”

Adrian Hastings, Natural Law, Oxford Companion to Christian Thought, Oxford 2000.


Craig Boyd
Craig Boyd

“The final element of the participation structure is that the participant
[= the human being] must have received the perfection from the source in question [=God]. In the case of the natural law, the perfection is reason’s capacity to know. That participation enables the agent to act freely and to govern her activities in accordance with reason. The ‘imago Dei‘ for Aquinas bridges the human and
the divine. He says, “That the human is made in the image of God . . .
implies that the human agent is intelligent and free to choose and govern itself”. This intelligence provides the continuity between the human and the divine. Since humans participate in divine reason by being created in God’s image, they are thereby enabled to understand that God commands the precepts of natural law because of the way in which God has created humanity.

Craig A Boyd, Medieval Christian Theologians, A Shared Morality. A Narrative Defense of Natural Law Ethics, Michigan 2007, pp 54-59.