Does moral theology need philosophy? What place does it have? What role does it play? In a word, what is the relationship between philosophy and theology in Christian moral doctrine? We could discuss these questions in a variety of ways. We think the simplest and most instructive is to examine a fully developed theological synthesis on these questions, such as St Thomas Aquinas', which can be taken as a model and is considered a classic: it is the direct heir to the theology of the Church Fathers and serves as a reference-point for modern theological currents. 

We can reduce the components of Thomistic moral teaching to four structural elements: 

1. Morality is essentially a response to the question of happiness and the ultimate end of human conduct, according to the general way morality was conceived by ancient philosophers and the Fathers. It is the treatise on happiness and the ultimate end. 

2. Man moves towards happiness through his actions on the basis of two kinds of principles corresponding to the two parts of the human act: the internal act and the external. First there are the internal principles or personal sources of action, which are the virtues. 

3. Then the external or superior principles of action come into play: law and grace. 

4. This structure presupposes an analysis of man as God made him, in his own image, with his different faculties that together make up a specifically human act: free choice. All the work of moral doctrine is aimed at informing, on the basis of universal principles, the choice that produces concrete action.

On each of these four points we will examine the place and role of philosophy in the Angelic Doctor's moral theology. 

In the five questions which make up the treatise on happiness, the role of philosophy, represented primarily by Aristotle and Boethius, appears so substantial that certain interpreters have regarded these questions as purely philosophical. They have not seen, first of all, that the study of the ultimate end and of the different goods offered to man form a threefold way — comparable to the five ways leading to the existence of God — bringing us to the Christian response: the call to the vision of God beyond this life, for "God alone" can fully satisfy the human longing for happiness. In dealing with this high point of his reasoning, Thomas no longer relies on the Philosopher, but on a theologian, on Augustine, who himself explains Catholic morality by starting with the question of happiness that every person asks himself, he says, even before expressing it. The One who can satisfy this longing is really the Trinitarian God, revealed and accessible in Jesus Christ. Nor did they consider that the explanation of the Beatitudes in the commentary on St Matthew was an underlying source of the Summa's treatise, that it was already following the plan of the progressive search for the true good in question 2, and was showing that only Christ revealed the complete happiness which the philosophers, including Aristotle, were unable to discover. Moreover, the treatise on happiness will only be completed in the explanation of the Gospel Beatitudes (q. 69), which St Thomas reserves for his exposition, with the aid of the virtues and gifts, of the Christian's happiness here below. 

Philosophy and theology, then, each play a large part in the treatise on happiness, but they are not simply juxtaposed; they are connected by what we could call a natural relationship. Together, in fact, they answer a question which arises from man's spiritual nature: what is the true good or genuine happiness? Enlightened by Revelation, the theologian perceives that this spontaneous desire can be fulfilled only by the vision of God because of the openness of the human intellect and will to the infinite. Hence the famous argument about the natural desire to see God, which is the mainspring of St Thomas' reasoning on this subject. Regarding this vocation, philosophy is both necessary and inadequate. It can neither attain nor even consider such a totally gratuitous and truly supernatural happiness. But although the theologian knows of the call to happiness in God by faith, he still cannot show the paths leading to it without the work of reason, without a philosophical reflection on acts and virtues. 

Organized in this way, the treatise on happiness provides the overall structure for the moral part of theology. We will thus find the connection we have just seen between philosophy and theology in each treatise of the Secunda Pars. 

Finally, we should note that this treatise on happiness will disappear from the post-Tridentine manuals of moral theology, as well as from the modern ethics of Kantian influence, following the critique of eudaemonism. It will only survive as the search for a material, empirical happiness advocated by utilitarianism. The Catechism of the Catholic Church has fortunately reintroduced the consideration of happiness at the start of its treatment of Christian morality as a vocation to beatitude in the light of the Gospel Beatitudes (CCC, nn. 1716-1729). 

The extensive treatise on habitus and virtues is a masterpiece of Thomistic moral teaching. There we find the heritage of ancient philosophy and the reflection of the Fathers, every one of whom saw virtue as the very essence of human and Christian perfection. Here again the role of philosophy is so substantial as to be considered preponderant. But in fact St Thomas' teaching on the virtues is the result of the patient search of medieval theologians guided by the gradually rediscovered works of Aristotle. Thomas uses the Stagirite's precise analyses even in their details, as in the treatise on prudence. In order to define and divide the related virtues, he will follow the lists drawn up by Cicero and Macrobius, which will make it difficult to find a place for Christian virtues such as humility, obedience and vigilance. The impression that the teaching on the virtues is mostly philosophical is even stronger, the more accustomed we are to thinking of virtue as being essentially the result of human effort, of repeated acts. 

However, when the treatise on the virtues is read as a whole, we see that it is mainly a theological construction. The virtues actually form a living organism comparable to the human body and its organs. They neither exist nor act separately, as one might suppose from an analytical study of the Summa. They are united by dynamic links forged by charity and prudence, and act together, like the limbs of our body. 

This consideration particularly applies to the relationship between the theological and moral virtues. Faith, hope and charity constitute the head of the Christian organism of the virtues and impart life from within, like a vital impulse, to the human virtues so that they can be ordered to divine happiness, but not without transforming them to some extent. St Thomas will have such a strong sense of this influence that he will consider it necessary for the infused moral virtues to be added in order to perfect the acquired virtues. In each treatise on the moral virtues, we will see the changes he makes with respect to Aristotle. Thus martyrdom will become the supreme act of the virtue of fortitude instead of courage in warfare, and virginity for Christ will be the perfection of chastity. Thomas will even maintain that there can be no true patience without charity and, thus, without grace (lla-llae, q. 136, a. 3). 

Moreover, St Thomas links the virtues with the gifts of the Holy Spirit, which thus enter the organism of the virtues in order to perfect them. The gifts are an integral part of Thomas' moral teaching, in accordance with the definition of the New Law as the grace of the Spirit, and are necessary for all Christians. They add a receptivity to the virtues, a docility to spiritual impulses. In this way the Holy Spirit's action, like the virtues, can affect all that the Christian does. Morality truly becomes "life in the Holy Spirit", as the Catechism calls it (n. 1699). Here we see no separation between morality and mysticism, to which the gifts will be reserved by later theology. 

In fact, under the influence of Revelation and Christian experience, the very idea of virtue is transformed: to the acquired virtues are added the infused virtues which originate in the grace of Christ and no longer in human effort alone. These virtues, beginning with the theological ones, are so vitally linked to the human virtues that their action will be the work of God and man together, united in charity. 

Finally, we should note that the apostolic catechesis (cf. CCC, n. 1971), particularly St Paul's teaching on virtue and vice in the Letter to the Romans, whose commentary prepared the Summa Theologica, represents the source, the principal "authority" for St Thomas' doctrine, together with the explanations of the Fathers, particularly St Augustine, St Gregory the Great, etc. The Thomistic study of the virtues thus combines the leading scriptural, philosophical and theological currents. 

Once again we find philosophy joined to Revelation within theology according to St Paul's command: "Your thoughts should be wholly directed to all that is ... virtuous or worthy of praise" (Phil 4:8); but also in the idea that the Word of God deepens philosophical knowledge and develops it beyond human thoughts and hopes. 

In Christian teaching the Decalogue has always been considered a basic foundation, and scholastic theology related it to the natural law inscribed in every human heart. Post-Tridentine theology made the Decalogue the cornerstone of moral teaching to the point of dividing its material, no longer according to the virtues as St Thomas did, but according to the Ten Commandments, interpreted as the expression of obligations and prohibitions imposed on man by God's will. 

St Thomas likewise assigned an essential place to the Decalogue and the natural law; but he puts them in a broader legislative context which makes them dependent on Christian Revelation. In his view, laws form a true organism which has its origin in God and his eternal law. The latter is known to man in the natural law, which will serve as the basis of human laws. Revelation will clarify, corroborate and perfect this legislation in the form of the Old Law, concentrated in the Decalogue, and of the New or Gospel law, taught chiefly in the Lord's Sermon on the Mount. The New Law represents the apex of the moral law and brings the divine law to its perfection here below. The Decalogue and the natural law are thus taken up into the legislative dynamic which has its source in God and returns to him through the New Law. This results in a reinterpretation of the Decalogue in the sense of an interiorization and a higher perfection. For St Thomas, the Decalogue sets out the rules for external acts which the New Law brings to perfection by governing the internal acts that inspire them, with the help of the virtues beginning with faith and charity. Thus the Decalogue is made to serve the virtues. It plays a particular role in the first stage of the divine pedagogy, in the training of beginners who must struggle against their sins and eradicate their vices. 

The philosophical part of Christian moral teaching mainly concerns its foundations, the natural law and the Decalogue that expresses it, by putting it in the context of the covenant. Its task will continue in the establishment of civil law by way of deduction or addition, which will be specifically the work of reason. Added to this is reflection on the virtues, which calls for experience and maturity. 

Let us note that the natural law does not appear as a barrier to freedom but, in St Thomas, possesses a basically dynamic nature: it proceeds from the natural inclinations and yearnings for the preservation of being, the gift of life, the good, truth, and life in society, which are already found in Cicero's De Officiis (bk. I, ch. IV). These inclinations will be developed through the virtues. As for the negative commandments, they forbid actions incompatible with the formation of the virtues and thus lay the groundwork for them. In this way, the natural law and the Decalogue can be ordered to the Gospel Law as to a higher perfection, a total fulfilment. Here as well, theology takes up and completes the philosophical quest. 

Lastly, we should mention the sapiential nature of law in St Thomas: it is the organizing function of reason on the part of the divine or human lawgiver, and not a mere act of will by one who holds authority, as will generally be the case in the modern conception. This results in an equally sapiential obedience, combining reason and will. The coordination of the different philosophical and theological levels of moral legislation will be the work of this wisdom. 

The principal task of practical reason in the moral realm consists in applying precepts to personal action in concrete circumstances. We can think of this operation as a deduction starting from the first principles of the moral order, on condition that they are linked to the natural inclinations which form the basis of the law and the first source of human action. These principles, then, are not theoretical and abstract, even if their foundation is universal and appears impersonal. They correspond to the meaning of truth and goodness, to love of self and others, which are natural to man and derive from that spiritual spark which St Thomas calls synderesis. 

The task of applying the principles of practical reason is the work of prudence integrating the data of moral science and of conscience, the interior witness of the law. It is not limited to determining what is permitted or forbidden, but searches for excellence, a certain perfection of action in the existing situation, as a craftsman seeks to make something good by plying his trade. Such work calls for intelligence, experience, effort and attentiveness. This is why moral action requires the involvement of all the subject's faculties and the use of the external abilities acquired, among other things, by education. 

Prudential judgement is different because it goes beyond ideas, however beautiful they may be, beyond intentions, counsels and commandments, however judicious they can be, to a decision to act, which gives rise to action and transforms the acting subject: it makes him a better person and enables him to grow. This is why true prudence needs the other virtues which particularly govern affectivity. We can say that prudential judgement or choice is all-encompassing; it engages the human person with his whole being, the past he has inherited, even his unconscious. A person's character is judged by his actions, as a tree is known by its fruits. 

The all-encompassing nature of concrete action requires the joint intervention of philosophy and theology, of reason and faith in the Christian moral judgement. The study of "cases", in particular, cannot be limited to a rational analysis or a material application of revealed principles. It requires the exercise of faith, which receives the light of the Spirit, and of reason, which reflects and seeks to discover in concrete terms what is good, what is the best thing to do. Therefore the Christian moralist should assimilate the teachings of the Gospel, which is often so concrete in its very formulation of principles, and reflect with his philosophical and scientific sources, all the while knowing that this work will be incomplete and even useless, if he does not take pains to put his personal prudence into action, which alone will enable him to experience and enjoy good results. 

In the First Letter to the Corinthians, St Paul offers us an excellent example of what could be called apostolic casuistry. In his examination of the different cases submitted to him, his method is always the same. It could be characterized by the compenetration of two levels: first, criteria of the rational order such as can be found in the philosophers and rabbis. In the case of fornication, for example, he will write: "Every other sin which a man commits is outside the body; but the immoral man sins against his own body" (6:18). But criteria drawn from faith also come into play: "Do you not know that your bodies are members of Christ? ... Do you not know that your body is a temple of the Holy Spirit?" (6:15, 19). Thus we can see that in St Paul's discernment there is a close connection between the meaning of what is human and the meaning that stems from Christ, each assuming the other and reinforcing it. But the Christian criteria will predominate, particularly through the action of charity uniting believers as brothers and sisters, as members of one body under the impulse of the Holy Spirit. 

As we can see, there is a very close association between philosophy and theology in the moral teaching of St Thomas. Far from being separate, much less in competition, these sciences work together through what we could call a vital integration of philosophy and theology. At the prompting of the theologian, the philosopher comes to reflect on the fundamental questions about the purpose and meaning of life, about good and evil, about happiness and suffering, about death and the afterlife, and he no longer thinks that only he can offer a complete answer to these problems. The theologian, for his part, needs the philosopher in order to learn how to use his reason with rigour and insight as he investigates the human dimensions of action and to provide him with the necessary categories and language for a sound explanation of the riches of the Gospel and the Christian experience. 

This sort of association between philosophy and theology is based on St Thomas' maxim: "Gratia non tollit, sed perficit naturam", which could be rephrased: theology does not destroy, but perfects philosophy. In our opinion, however, the principle should not be understood in the sense that philosophy, as a work of reason, must first be constructed while saying to oneself that in any case it will be confirmed by grace, but rather in the opposite sense: we must have the boldness to believe in the Word of God and to abandon ourselves to grace, in the assurance that, far from destroying whatever is true, good and reasonable in philosophy, grace will teach us how to make it our own, to develop it and to perfect it, while revealing to us a broader and more profound wisdom than any human thought, the wisdom given by the Holy Spirit who unites us with the person of Christ and his Cross by teaching us to "live in Christ".