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Conscience Working within Prudentia—Instructed by Thomas Deman’s Reading of Aquinas

Loyola Institute, Trinity College, D02 PN40 Dublin, Ireland
Religions 2022, 13(9), 875;
Received: 1 August 2022 / Revised: 19 August 2022 / Accepted: 9 September 2022 / Published: 19 September 2022


The French Dominican Thomas Deman (1899–1954) argued for the restoration of the virtue of prudentia against a background of moral theology and philosophy that, as he saw it, had replaced the centrality of prudenti a with a centrality of conscience. This article will follow Deman in his reading of Aquinas and develop an understanding of prudentia as a moral virtue of the intellect, which co-ordinates the good life, the moral life. Conscience is a moment within the performance of prudentia. The argument of the paper is that, while conscience and prudentia are both important for good human decision-making, they should not be seen as rival concepts but rather, conscience should be understood as working within the virtue of prudentia. Specifically, the argument is that the role of conscience passes into the practical order only when it is enacted via the virtue of prudentia.

1. Introduction

‘And we think, that the person of prudentia, as we have understood it above, presents an image of a person more fulfilled and more just than the person of conscience.’1
These are the words of the French Dominican Thomas Deman (1899–1954) toward the end of his intensive study of Thomas Aquinas’ treatment of prudentia in the Summa Theologiae Secunda secundae qq. 47–56. In this commentary, as yet untranslated, Deman is profoundly critical of the centrality of ‘conscience’ in the Catholic moral systems of his time. A key argument made in his commentary is that the centrality of the virtue of prudentia has been lost from view in Christian living. Writing in the 1940s, it is Deman’s argument that in the moral systems he has inherited, treatments of conscience have replaced ‘la prudence de la Somme théologique’, with devastating consequences for human living, changing the very understanding of how to live well as humans.2 In Deman’s view, it is prudentia, at once an intellectual and a moral virtue, that guides a person in the various complex decisions encountered in seeking to lead a good life, that is to say, a life pleasing to God. Deman’s concern is to establish an accurate reading of Thomas Aquinas on prudentia wherein it lies at the centre of, and coordinates, the good life, the moral life.3 Conscience’s role, Deman argues, is best understood as working within the virtues. Specifically, his argument is that the role of conscience passes into the practical order only when it is enacted via the virtue of prudentia.
This article will first provide some brief biographical background to Thomas Deman op. This will be followed by an account of prudentia in the thought of Aquinas, as read through Deman’s eyes. Attention will then turn to Deman’s exposition of conscience; particular focus will be on the section entitled ‘Coordination de la conscience à la prudence’.4 The habitus of synderesis, the principle by which we are orientated to the good, will be identified as the foundational commonality shared by conscience and prudentia.
The final section will turn to Deman’s distinctive contribution. While Aquinas does not directly link conscience with prudentia, Deman argues that there are resources in Aquinas’ work that can properly situate the working of conscience within the working of prudentia.
The Latin term prudentia will be retained throughout, as in English, the word ‘prudence’ has acquired a meaning more akin to caution, care, preferring safety to change. This, as Daniel Westburg notes is ‘a miserable sort of prudence, self-protective, preferring safety to change, far removed from Thomistic prudence’.5 Constant vigilance is needed to avoid carrying into discussion false notes of a current English usage. Deman makes a similar observation in regard to the French la prudence.

2. Thomas Deman6

Thomas Deman (1899–1954) was of the generation of French Dominicans that included Marie-Dominique Chenu and Yves Congar. Born in Roubaix in the north of France in 1899, Albert Deman took the name of Thomas on receiving his Dominican habit in 1921. Deman taught theology at Le Saulchoir, firstly in Kain, Belgium (1928–1939), and continuing at Le Saulchoir following its return to France in 1939, where it became based at Étoiles, near Paris. He moved to Fribourg in 1945, where he taught until his death in 1954. His death at a relatively young age may explain why his writings have not had the impact they merit.
Living in a time of turmoil, amidst the horrors of the Second World War in Europe, Deman published Construction de la Paix (Deman 1939), Le Mal et Dieu (Deman 1943) and Pourquoi nous croyons à la Providence (Deman 1946). In 1948, his essay entitled “Pour une restauration de la vertu de prudence” was published in Prudence chrétienne.7 His work on prudentia continued to deepen and develop in his 1953 essay on the reality of the practical nature of prudentia in “Le ‘précepte’ de la prudence chez saint Thomas d’Aquin”.8 (Deman 1953) This article will focus on Deman’s intensive study of Aquinas’ Summa theologiae, Secunda secundae qq. 47–56, first published in 1949, where he pays particular attention to the relationship between prudentia and conscience.

3. ‘La Prudence de la Somme Théologique’9

Deman draws attention to the fact that Aquinas attends to the virtue of prudentia in many places in his writings. He treats of prudentia for the first time in his Commentary on the Sentences (Paris, 1254–1256), amidst his study of the virtues in Book 3. Aquinas attends to prudentia in his Commentary on the Nicomachean Ethics (Paris, 1269). In the disputed question De virtutibus in communi (Italy, 1266–1269), article 6, he establishes the necessity of a virtue for the practical intellect. Commenting on this text, Deman draws attention to Aquinas’ ‘remarkable statement’ that prudentia causes the moral virtues. In the disputed question De virtutibus cardinalibus (Paris, 1269–1272), Aquinas again considers the virtue of prudentia. He also addresses prudentia in various places in his biblical commentaries.10
In the Secunda secundae of the Summa theologiae, questions 47–56 are dedicated to discussion of the virtue of prudentia. The groundwork for this treatment is established in the Prima secundae, where he addresses virtue in general (see ST I-II qqs 55 ff). It is important to begin with this foundation, because in any consideration of virtue in Aquinas, it is essential to remember the core definition—virtue is that ‘which makes the possessor good, and their works good likewise’ (ST I-II q. 56 a.3 c).11

3.1. Prima Secundae

From the Prima pars we learn that prudentia is an intellectual virtue of the practical intellect, perfective of the reason, and necessary if a good life is to be lived.
The teaching is unequivocal; amidst the ‘general’ discussion of virtue, in question 57 of the Prima secundae, prudentia is identified as
a virtue most necessary for human life. For a good life consists in good deeds. (Bene enim vivere consistit in bene operari) Now in order to do good deeds, it matters not only what a human does, but also how they do it; to wit, that they do it from right choice and not merely from impulse or passion. And, since choice is about things in reference to the end, rectitude of choice requires two things: namely, the due end, and something suitably ordained to that due end. Now the human is suitably directed to their due end by a virtue which perfects the soul in the appetitive part, the object of which is the good and the end. And to that which is suitably ordained to the due end the human needs to be rightly disposed by a disposition in their reason (habitum rationis), because counsel and choice, which are about things ordained to the end, are acts of the reason. Consequently an intellectual virtue is needed in the reason, to perfect the reason, and make it suitably affected towards things ordained to the end; and this virtue is prudentia. Consequently prudentia is a virtue necessary to lead a good life.
(ST I-II q. 57 a.5 c)12
Prudentia is a virtue and, as such, it makes a person act well, not merely to have the aptness to act well. In this, it makes the possessor good. Another reader of Aquinas, Marie-Michel Labourdette, notes that alone among the virtues of the intelligence, prudentia has the quality of virtue ‘absolument’ (simpliciter), that is to say, prudentia is formative not only of one’s intelligence, but also of one’s very self, of the person themselves.13 Growth into the virtue of prudentia means not only that one becomes good at decision-making, but that one desires the good, and thus one’s very humanity flourishes: ‘prudentia is necessary to humankind for living well, and not only for doing good things, for acting well’ (ST I-II q. 57 a.5 ad 1).14
In summary, for Aquinas to refer to someone as a person of prudentia is to speak of someone who acts well. For Aquinas, acting well is living well, Bene enim vivere consistit in bene operari. Prudentia, Deman reads Aquinas as teaching, ‘is the sign of one’s soul’.15 It is in witnessing someone exercise this virtue that we see the type of human being they are, who they have become—their character. One can be a great mathematician or a great artist or a great sportsperson, but this does not necessarily imply that one is a ‘great’ human being. For Deman reading Aquinas, this is precisely what prudentia gives: the beauty of human flourishing, the beauty that pertains to a person harmoniously and universally developed. The virtue of prudentia coordinates, guides and enables a person to live well as a human being. One becomes a good person, simpliciter. Deman comments that, for Aquinas, prudentia is essential for Christian living.16 It is precisely on these grounds that Thomas Deman advocates the restoration of prudentia and speaks of the centrality of prudentia in the living of a good life.

3.2. Secunda Secundae

On this strong foundation established in the Prima secundae, Aquinas proceeds in the Secunda secundae to explore, first, in detail, the virtue itself, (ST II-II qq. 47–51), then, the associated gift of the Holy Spirit, counsel (ST II-II q. 52, donum consilii), followed by the vices attendant to prudentia (ST II-II qq. 53–55). This follows his usual method: first the virtue itself, then the gift, next the vices, followed by a question on the precepts (commandments; de praeceptis) pertaining to prudentia (ST II-II q. 56).
Deman affirms that, for Aquinas, prudentia is an intellectual virtue, ‘prudentia, properly speaking, is in the reason’ (ST II-II q. 47 a.1 c).17 Prudentia, perfected by memory and experience (interior senses), judges promptly of particular circumstances (ST II-II q. 47 ad 3). In matters of morality, this virtue of decision-making is essential, as there is inevitably a certain instability in matters of morality. As Deman puts it, a particular circumstance can seem to render inapplicable a principle that had been believed to be universally valid.18 The contingent upsets (déconcerte) fixed principles.
In his consideration of human action in the complexity of circumstances needing to be considered in good human living, Aquinas makes an important observation: the truth of the practical intellect depends on conformity with right appetite (ST I-II q. 57 a.5 ad 3).19 Intellect and will work together; the will orientates the person to desire the right ends, while the intellect, through the virtue of prudentia, enables the person to make the right choices for that end, and to act on them.
For human action, three acts of reason, of intellect, are called upon: the first is to take counsel, the second is to judge of what one has discovered and the third precept or command ‘consists in applying to action the things counselled and judged’ (ST II-II q. 47 a.8 c).20 Counsel (inquiry) and judgement, for Aquinas, are in the speculative intellect, while command is proper to the practical intellect, in so far as the practical intellect is ordained to operation. The virtue that perfects the command is prudentia (ST I-II q. 57 a. 6 c).21
Thus, the proper act of prudentia is command. ‘Command is an act of the reason, presupposing an act of the will, in virtue of which the reason, by its command, moves (the power) to the execution of the act’ (ST I-II q. 17 a.1 c).22 Intellect and will interact in command. While the will—my desires—may tell me ‘do this’, it is prudentia, a virtue of reason, that will advise me or inform me that this is what needs to be done, for this end. This is how a reasonable person acts. As Deman puts it, reason reigns in a human being; from counsel and judgement to command there is a progressive deployment of an activity, that, in each of its various moments, carries the mark of a reasoning being.23 Prudentia is performative.
In summary, thus far, Deman’s argument is that prudentia, an intellectual virtue, not only enables one to reason toward a good act; it is itself the art of skilful living. Acting out of virtue not only makes the action good, but makes the person good. Deman highlights this teaching of Aquinas in a context of moral theology wherein he believed that voluntarism had come to be accepted as the guide to good human living, a world wherein the virtues of obedience and humility were exalted by Christians. This is the context in which he draws attention to this
teaching of the greatest importance. Because perhaps nothing has become of less importance to us, than this thought, primordial and uncontested for St Thomas, according to which, to be good and virtuous, we must take care of our intelligence … nous avons à prendre soin de notre intelligence.’24

4. Conscience and the Demise of Prudentia

Deman’s concern is with the resources needed to live a Christian life well, and with how these can be developed. He sees the thinking of Thomas Aquinas on the virtue of prudentia as contributing importantly to this task. Prudentia is a virtue of decision-making, an exercise of the intellect. In this regard, he considers how the faculty of conscience is best understood in relation to the virtue of prudentia, the prudentia à la Somme theologiae. It is his assertion that the person of prudentia is a more complete, a more ‘whole’, person than the person of conscience. It is largely his reading of Aquinas that leads him to this understanding. As shown above, Deman was in agreement with Aquinas in regard to the centrality of the virtue of prudentia in the living well of a human life, in the moral life. This is why, in 1948, he published his essay entitled “Pour une restauration de la vertu de prudence”. It was evident to him that prudentia had lost its centrality in moral discourse. Deman identified two core reasons for this. Firstly was the focus and the privileging of the will as a moral faculty, which resulted in a corresponding depreciation in the role of the intelligence in moral matters. Secondly, he noted that in handbooks of moral theology, the treatise on prudentia had decreased in proportion as the treatise on conscience increased, as if, he notes, they were two rival notions.25 This is not Deman’s view. In his task of restoring the centrality of prudentia, Deman is not working with two rival notions, conscience on the one hand and prudentia on the other, seeking to remove one to allow the other to flourish. He sees his task as to resituate a ‘recovered’ notion of conscience within the work of prudentia.

5. The Evolution of the Concept of Conscience

Deman approaches his study of conscience utilising the same methodology as he did in his earlier work on prudentia. That is, he first traces the history of the way the term has been understood over the generations to his time. The scholarship is detailed. It suffices to draw attention to some significant points. Beginning with the Greeks, we are informed that the term συνείδησις (suneideisis) appears for the first time in a fragment of Democritus. While it is difficult to be sure, this term seems to have been understood as having a moral meaning, specifically linked to the idea of remorse. Amongst the Greeks studied, Deman observes that, at this stage, rarely, indeed if ever, is conscience understood as something exercised prior to action, directing action or guiding a life. It is understood as a judgement made after an event.
Thomas Deman then invites the reader to consider the remarkable absence of the term from Aristotelean ethics; he comments that Aristotle developed his moral teachings independent of the notion of conscience. In Aristotelean thought, it was right reason, orthos logos, phronesis (prudentia) that played the role of ensuring ‘le perfectionnement pratique’, practical perfection, that is, good human action.26 Cicero is accorded credit for creating the word conscientia in Latin. Henceforth, the term is found frequently among the Latin philosophers, often but not always carrying a moral signification. Cicero has written of recta conscientia, bona conscientia and mala conscientia; for Cicero, conscience is good or bad depending on the object to which it relates.27 This language of good conscience or bad conscience seems to have become understood as referring to a certain presence of a moral law interiorly; each of us judges ourselves, internally. Our internal conscience will see evil and judge; it will accuse the guilty and torment them.28 Here again, among the Latins, the idea of remorse identified by Democritus and the Greeks is evident.
Notably, Deman observes that the Latin authors never consider conscience in the role of preparing for action. That the ancients understood judgements on past actions to inspire future conduct is not in question, nor that they understood the importance of looking forward and acting reasonably in light of what they want to do—but this, Deman is clear, was not deemed the task of conscience.29
Entering into the world of Christianity, the word συνείδησις appears often in the Greek Testament, in particular in the work of St Paul. Paul received an understanding of συνείδησις as a gift of nature, a judge of actions. It is to be understood positively—while that which it judges may be bad, συνείδησις is good. Paul augments this received understanding. One idea Paul introduces is that while in the received positive tradition συνείδησις/conscientia had come to be accepted as something infallible and incorruptible, Deman points out that, for Paul, συνείδησις/conscientia can be the subject of errors such as cowardice.30
Perhaps most consequential is the movement in Paul’s writings toward an idea of the antecedent conscience, that is, συνείδησις/conscientia involved not only in judging human conduct done, but also assuming a regulating role in terms of what one might do. Paul uses the expression διά την συνείδησιν three times in the epistles, (Rom 13:5; Cor. 10: 25; 10: 27; and in Cor. 10:28 he speaks of καὶ τὴν συνείδησιν) for consciences sake, on account of conscience, in this way allotting the role of cause to συνείδησις/conscientia in relation to actions that a person must take.
It is Deman’s contention that these are the first references in the history of moral theology to the antecedent conscience. This development in thought leads to the important suggestion of the need for education of a person’s conscience. The natural gift of conscience is insufficient. The education will provide knowledge in regard to a situation; conscience then must be the practical application of this knowledge. The antecedent conscience has an intellectual content, and thus there is a need for education, formation. ‘Ne sommes-nous pas tout proches de la prudence?’, are we not very close to prudentia, Deman ponders.31 Thus, from his work on the thought of St Paul, Deman is already making an argument toward an important relationship between conscience and prudentia.
This insight did not make an easy transition into Christian thought. Moving on from St Paul, Deman observes that, while the language and concept of συνείδησις/conscientia may be seen to have entered into the Christian tradition from the New Testament, the inherited understanding still tended to focus more on consequent conscience than antecedent conscience; it is less St Paul’s developments, he argues, than the thought of Cicero and Seneca that were recalled by the early writers such as Ambrose, and indeed on into the Middle Ages.
On the other hand, Deman notes that Thomas Aquinas, in the many places where he addresses the concept of conscience, demonstrates that he is familiar with the enhanced understanding introduced by St Paul.32 This is evident in the commentaries on Paul’s epistles, where Aquinas writes of the antecedent conscience (On Rom 14, lesson 2, and On Galatians 5, lesson 1).33 In the Summa Theologiae ST I q. 79 a.13, he treats of the nature of conscience in a question on intellectual power, and in ST I-II he writes of rectitude and obligation of conscience in a question on the morality of the human act (ST I-II q. 19 a.5, 6). All this makes clear that in Aquinas’ work, there is an understanding of conscience in a role as guide to human living, as preparation for action.
At the same time, Deman is clear: the tradition Aquinas encounters in investigating conscience is different to that which led him to his insights on prudentia, and there is no indication in his writings of any attempt to bring these two concepts, conscience and prudentia, together, nor any indication that he sought to unify them. This is the task to which Deman turns next. He can do this because of his appreciation of Aquinas’ attention to St Paul’s enhanced insights in regard to the notion of conscience.

6. The Coordination of Conscience within Prudentia

Before proceeding, it is helpful to recall the distinction Deman has made in theories of conscience. There is one school of thought that focuses on what Deman terms ‘consequent conscience’. Consequent conscience refers to a person’s reflection on actions already performed. A second school of thought is concerned with the working of conscience prior to the performance of an action. This is termed ‘la conscience antécédente’, antecedent conscience; it is in this understanding that conscience has a role in regulating human living and not only in judging actions after they have been performed.
Aquinas’ writings on conscience encompass both uses of the term. He speaks of conscience in terms of to bear witness, testificari, to excuse, excusare, to accuse, accusare, and in terms of remorse, reprimand, remordere, reprehendere. All these terms imply reflection on an action already accomplished. This is reminiscent of Democritus—an action once performed, the person themselves judges their action, satisfied if they have done well, condemning themselves if they have acted badly. Deman observes that Aquinas does not make any significant developments to this ‘universal and uncontested teaching’ of the Middle Ages. For example, the Summa theologiae Prima Secundae q. 87 a.1 refers to remorsus conscientiae, and in q. 21 a.4, we read that a good act gains merit in God’s eyes, a bad one, demerit. This understanding of conscience as consequent conscience opens no possibility for relationship with prudentia. Prudentia’s focus is preparation for action and decision to act, not judgement after the action, leading Deman to conclude that while there is no connection between the work of prudentia and that of consequent conscience, he is still clear that there is reason for both to exist.34
It is different when it comes to ‘la conscience antécédente’, the working of conscience prior to performance of an action. Deman notes that in ST I q. 79 a.13 c, where Aquinas considers conscience as the application of knowledge to what we do, Aquinas attributes to conscience the power of binding, ligare, and of inciting to action, instigare. It is by means of conscience thus understood that one judges whether a thing is to be done or not done; judicamus aliquid esse faciendum vel non faciendum (ST I q. 79 a.13 c). As Deman has shown, in his writings, St Paul demonstrated such an understanding of conscience.35 Aquinas used the term ‘application’; conscience is knowledge applied to an individual case, to a particular act, and its special role is to bring into play our general understanding of human behaviour in judging how to act: ‘all these (the different acts attributed to conscience) follow the application of knowledge or science to what we do’ (ST I q. 79 a.13 c).36
In this same article, Aquinas links conscience to synderesis. Synderesis is the habitual grasp of first moral principles: “all the habits by which conscience is formed, although many, nevertheless have their efficacy from one first habit, the habit of first principles, which is called ‘synderesis’”(ST I q. 79 a.13 ad 3).37 In a critical vein, Deman notes that in the corpus of ST I q. 79 a.13, and in ad 3 of the same article, Aquinas too easily substitutes the term conscience for synderesis and, thus, Deman argues that Aquinas has to develop an elaborate doctrine to explain the distinction between synderesis and conscience.38
A brief word on synderesis (συντήρησις). This concept is said to have been introduced by St. Jerome to Christian thinking through a gloss on Ezekiel’s vision of four creatures emerging from the heavens, each with four faces: a man, a lion, an ox and an eagle (Ezekiel 1: 4–14). Interpreting this vision, Jerome writes that the eagle represents that “spark of conscience” (scintilla conscientiae) that makes us aware of our sinfulness when reason, spirit or desire become disordered. This concept came to be named in medieval manuscripts “synderesis”. Thus, synderesis came to be understood as an innate orientation towards goodness, which, while it can be impeded, cannot be completely eradicated. It continues to exist in even the most sinful people. Deman identifies this principle of synderesis as pivotal in relating Aquinas’ understanding of prudentia and his understanding of conscience within an account of human decision-making unto action. Synderesis is the principle by which we are orientated to the good. Synderesis is prudentia’s foundation, synderesis movet prudentiam sicut intellectus principiorum scientiamsynderesis moves prudentia, just as the understanding of principles moves knowledge (ST II-II q. 47 a. 6 ad 3)—and, as just noted, he writes in Summa theologiae q. 79 a.13 that all the habits by which conscience is formed have their efficacy from the habit of first principles, synderesis (ST I q. 79 a.13 c ad 3).
It is thus very important to get synderesis ‘right’.39 Vernon J. Bourke in “The Synderesis Rule and Right Reason” importantly notes that synderesis ‘cannot of itself be the source of our knowledge of what is good or evil … it is a formal principle with no specific material content’ (Bourke 1983).40 Bonum, the good, is concrete: it refers in a theological context to what is fitting to a human agent working for the attainment of beatitude, happiness. However, ‘there is no intellectual knowledge prior to sense experience’.41 The habit of synderesis is an intellectual skill; it enables us to ‘see’ what ought to be done, but it is ‘only after one has experienced something of the world and human life that the knowledge of synderesis can be developed.’ (p. 75) This brings us back again to the need for education, for formation into the practices of conscience and of prudentia.42

7. Conscience Working within Prudentia

While Aquinas does not directly relate the act of conscience with the virtue of prudentia, Deman sees within Aquinas’ corpus the resources to do this. Deman’s central argument is that conscience works within prudentia, where prudentia is understood as the virtue that guides a person in the complex decision-making processes necessary for the living of a good life. Conscience might be understood as an act, a moment within the exercise of the virtue of prudentia in the living of a good life. For Aquinas and Deman, a good life is a life pleasing to God.
In comparing the distinctive contributions of prudentia and conscience to decision-making, Deman addresses two main issues. First, he explores the risks attendant to a false conscience, risks he argues are much minimised by the exercise of the virtue of prudentia in decision-making. Second, he highlights the fact that prudentia always ends in action: conscience with judgement.
As has been established, for Aquinas, conscience is an act, an act of judgement that this is a good thing to do. This judgement can be mistaken—it can be the case that this is not a good thing to do. This mistake, Aquinas states, can come about in two different ways. Firstly, the reasoning process can be flawed; secondly, the act of conscience can be mistaken due to the strength of a disordered appetite.
Deman elucidates as follows. The reasoning process can be flawed when it has been based on false propositions, such as that the taking of oaths is against divine law. While based on true propositions, the reasoning process may also be false, in a failure to apply general principles to contingent situations (see De Ver q. 17 a.2). In the case of disordered appetite, a disordered desire can lead a person to opt for fornication, an act they know is wrong. ‘In such a case the integrity of the conscience is at war with the lawlessness of the desire.’43
Aquinas’ core teaching regarding the close connection between reason and desire is maintained; a corrupt appetite can provide for itself the reasons that it needs. The sinner can convince himself that this is the right action to take, that they would be mistaken to act otherwise, and so they can blind themselves to the warning of conscience, creating, as it were, a ‘false conscience’.44
Nevertheless, the constant teaching is that the judgement of conscience has binding force. Aware of the possible dramatic consequences, Aquinas upholds this teaching. It follows that a false conscience, no matter why it is false, always obliges.45 The judgement a person makes in regard to an action to be done or forbidden is binding. Aquinas’ understanding of the tight interconnection in the workings of reason and will is again evident. It is of the nature of the will to be conditioned and regulated by the judgement that reason makes. The object of the will is that which is set before it by the reason (ST I-II q. 19 a.5 c)46—and the will is never permitted to act against the judgement of reason. Deman comments that Aquinas’ example to illustrate this teaching is bold, yet effective: should a person judge that it is wrong to believe in Christ, and nevertheless believes in him against the dictates of his conscience, he sins.47 This is so because, according to the judgement of his conscience, he has consented to evil.
Simply put, to act against one’s judgement of conscience is wrong.
Deman sees the complexity of this inward binding nature of conscience. He writes: ‘In Christian theology, where reasonable law (règle raisonnable) is but a derivation of divine law, the obligatory force of conscience is but an expression of the will of God’.48 Antecedent conscience, conscience understood as directive of action, is at once subject to error and endowed with a force of obligation. It follows that a person with a false conscience will sin whatever they do. This highlights the urgency of ensuring that one’s conscience is true (‘vraie’). This, Deman notes, is one’s duty. It is each person’s responsibility to form their conscience rightly. This leads Deman to ask how can a person reform a false conscience, to ensure that, as often as possible, the right judgement is made? Conscience alone has been shown to be insufficient.
Deman writes: ‘It is precisely here that prudentia fits in. Prudentia was conceived and defined as the virtue that ensures all the qualities permitting a person to act responsibly and with the greatest chance of success—that is, with a blameless conscience.’49 In short: becoming a person of prudentia is the way for someone to avoid becoming a victim of false conscience.50 For, while both conscience and prudentia can be subject to error, the risk of error is much greater when it comes to conscience.
Prudentia is the virtue that gives a person the best chance of acting humanly, and of acting with an irreproachable conscience. Deman justifies this claim as follows. Prudentia is a virtue of the practical intellect. Formation into the virtue of prudentia leads a person to acquire the skill, a habitus of the reason, which enables the intelligent application of general rules to particular situations. This means that a person must first be schooled in the general principles so that these can be applied to particular situations appropriately. Appropriately informed and formed, a Christian will no longer mistakenly think that oaths are forbidden by divine law. The intellectual cause of error is eliminated in the person of virtue. In a further clarification, Deman emphasises that his concern is not with a theoretical discussion about rules, norms and acts, but with a programme of moral education, one which respects the intellect, the reason.
A disordered desire is another source of error in the judgement of conscience. In a person of disordered desire, where someone tries to resist the inclinations of the appetite, inwardly protesting against immoral actions, Deman notes that conscience is most visible. A person can be torn apart—they see and judge the right way to act, but then act differently. The exercise of the virtue of prudentia, he argues, helps to avoid the tension and the strain in this situation. As a moral virtue in the intellect, in line with Aquinas’ teaching on the interconnectivity of the virtues, we can say that in a person of prudentia, the other moral virtues are also active, and so desires are properly ordered. As Deman phrases it, referring to a person with the virtue of prudentia ‘L’unité règne en sa vie.’51 The knowledge that fornication is wrong leads a person of prudentia to avoid it; counsel and judgement are accomplished in precept, in a good action effectively accomplished. Reason and desire work together to good action. As such, Deman advises that both reason and desire must be educated.
This is key; while conscience sees and judges, decides that such and such is the best action, it does not necessarily result in act. Prudentia brings judgment to act. In this sense, prudentia is ‘une conscience droite accomplie’—right conscience accomplished. (Deman, 503)
This is not to say that the person with prudentia is infallible. The virtue is always subject to error. But error in the virtue and a false disordered conscience are very different matters. When a person of prudentia fails ‘he fails because contingent facts are never wholly unambiguous, not because his moral education is lacking…. the errors of a prudent man are always excusable … for his intention is entirely virtuous. Only the error of a prudent man bears this saving mark.’52
A point Deman emphasises in all his work on prudentia is that prudentia ends in act; it is precept, command. The notion of conscience concerns itself with rules, interior moral rules to guide human behaviour, but does not concern itself with realisation. If we relied only on conscience there is no guarantee that a person will act well. We know only that a person of conscience, whether the conscience be true or false, will make a judgement in regard to what to do or not to do. In a person of prudentia, the judging process will be carefully monitored by the other virtues and if the judgement is true, it will be carried into effect. Thanks to prudentia, a person acts well. Deman surmises that the notion of conscience was not created to lead a person to act rightly. Hence his constant teaching that it is necessary to reintroduce conscience to its rightful place within human action, within the exercise of the virtue of prudentia.53

8. Conclusions

The purpose of this paper has been to establish the primacy of prudentia in living well. The primary source has been Deman’s French translation and commentary on the work of Thomas Aquinas. A secondary aim has been to establish that conscience and prudentia are not rival notions. Conscience is a vital act, a moment within prudentia’s performativity. While Aquinas doesn’t link these two notions, it is Deman’s view that in his work, there are resources to provide just such a link, to situate the act of conscience within the virtue of prudentia.
The exercise of the virtue of prudentia is good human behaviour, freely chosen, in concrete circumstances. The judgement of conscience passes into the practical order when it becomes an act of prudentia. That is what distinguishes the person of conscience from the person of prudentia. Conscience, in Deman’s reading, can cloak errant behaviour. Conscience can sometimes take the form of stubbornness. In people working according to conscience, there can be little discretion or subtlety in the exercise of conscience. Does it not happen that we sometimes complain that someone has too much conscience, is too conscientious?54 It is evident that this person still needs to acquire maturity in virtue. They do not yet have this easy movement, this ease associated with someone whose soul ‘is the mistress of their actions’. In a sense, a person seems less a person of conscience the more profoundly virtuous they are.55 Accomplishing with ease and aptitude good actions, it appears that they are following the inclination of their nature. In putting into practice their decisions, they exercise an exquisite sense of adaptation to circumstances—and because their prudentia is no less joined to the moral virtues than to the intellectual virtues, they do what is good with an impressive elegance, which speaks of maturity in virtue.56 The person of conscience can fail or be mistaken in this respect. Leaving the last word to Deman, one never says that it is dangerous to have too much prudentia—‘On ne dira jamais qu’il est dangereux d’avoir trop de prudence’.57


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‘Et nous pensons que l’homme prudent, selon qu’il a été expliqué ci-dessus, traduit un ideal plus complet et plus juste que l’homme consciencieux.’ (Deman et al. 2006), Appendice II, Renseignements techniques, 523. Deman’s translation and commentary has had three editions in French, most recently republished by Cerf (2006) with a preface by Jean-Pierre Torrell, op. First published by “Revue des jeunes”, Desclée, 1949, and again in 1957. This article is using the 2006 edition, with a Préface by Jean-Pierre Torrell op. Translations are mine, unless stated otherwise.
“On voulut de cette manière ‘faciliter’ la vie moral; en réalité, on en changea l’esprit.” Deman, ‘Avant-propos’, La Prudentia.
‘A l’encontre de ce movement, rien n’est plus souhaitable qu’une restauration du traité de la prudentia.’ Deman, ‘Avant-propos’, La Prudentia, 13.
Deman, Appendix II, ‘Coordination de la conscience à la prudence’, pp. 496–506.
For a brief overview of his life and work, see Jean-Pierre Torrell, Préface, in Deman, La Prudentia.
For a succinct account of prudentia in Thomas Aquinas, see (Porr and Aquinas 2016).
Deman, ‘Avant-propos’, La Prudentia, 8.
Et quia virtus est quae bonum facit habentem, et opus eius bonum reddit, huiusmodi habitus simpliciter dicuntur virtutes, quia reddunt bonum opus in actu, et simpliciter faciunt bonum habentem. (Aquinas 1947).
Respondeo dicendum quod prudentia est virtus maxime necessaria ad vitam humanam. Bene enim vivere consistit in bene operari. Ad hoc autem quod aliquis bene operetur, non solum requiritur quid faciat, sed etiam quomodo faciat; ut scilicet secundum electionem rectam operetur, non solum ex impetu aut passione. Cum autem electio sit eorum quae sunt ad finem, rectitudo electionis duo requirit, scilicet debitum finem; et id quod convenienter ordinatur ad debitum finem. Ad debitum autem finem homo convenienter disponitur per virtutem quae perficit partem animae appetitivam, cuius obiectum est bonum et finis. Ad id autem quod convenienter in finem debitum ordinatur, oportet quod homo directe disponatur per habitum rationis, quia consiliari et eligere, quae sunt eorum quae sunt ad finem, sunt actus rationis. Et ideo necesse est in ratione esse aliquam virtutem intellectualem, per quam perficiatur ratio ad hoc quod convenienter se habeat ad ea quae sunt ad finem. Et haec virtus est prudentia. Unde prudentia est virtus necessaria ad bene vivendum.
‘Seule parmi les vertus humaines de l’intelligence, elle a la qualité de vertu absolument (simpliciter), elle rectifie non seulement l’intelligence, mais la personne.’ (Michel Labourdette 2016, p. 15).
Prudentia autem est necessaria homini ad bene vivendum, non solum ad hoc quod fiat bonus.
‘Elle est le signe d’une âme’, Deman, ‘Les Connexions de la Prudence’, La Prudentia, (Deman, 2016, p. 422).
‘La prudentia à ses yeux est une pièce necessaire de la vie chrétienne.’ Deman, ‘Avant-propos’, La Prudentia, p. 12.
Quod prudentia proprie sit in ratione.
Deman, La Prudentia, p. 439.
Verum autem intellectus practici accipitur per conformitatem ad appetitum rectum.
‘La prudence dit ordre au bien formellement considéré; et elle confère plus que la faculté de délibérer, de juger, de commander comme il se doit, mais garantit le bon usage de cette aptitude.’ Deman, p. 457.
Manifestum est autem quod in his quae per hominem fiunt, principalis actus est praecipere, ad quem alii ordinantur. Et ideo virtuti quae est bene praeceptiva, scilicet prudentiae.
Unde relinquitur quod imperare sit actus rationis, praesupposito actu voluntatis, in cuius virtute ratio movet per imperium ad exercitium actus.
‘Mais la manière même dont il manifeste sa volonté achève de nous le faire connaître comme un homme en qui de nous le faire connaître comme un homme en qui règne la raison. Du conseil et du jugement au commandement, il y a le déploiement progressif d’une activité qui, en ses divers moments, porte al marque de l’être raisonnable.’ Deman, La Prudentia, p. 453.
‘A ce titre, elle constitue pour nous un enseignement de la plus grande importance. Car rien peut-être ne nous est devenu moins familiar que cette pensée, primordial et incontestée chez un saint Thomas, selon laquelle, pour être bons et vertueux, nous avons à prendre soin de notre intelligence.’ Deman, Avant-propos, La Prudentia, pp. 9, 10.
‘Tout se passe comme si l’on avait affaire à deux notions rivales. Deman, La Prudentia, p. 479.
Deman, 479.
‘La conscience est bonne ou mauvaise selon l’objet sur lequel elle porte.’ Deman, p. 484.
‘Qu’elle loue ou qu’elle condamne, il semble bien que dans tous les cas la conscience pronounce un jugement infallible.’ Deman, 486.
‘Mais ce n’est point cette tâche à laquelle ils députaient la conscience.’ Deman, p. 487.
‘Nous découvrons que la conscience est sujette à erreur comme à lâcheté.’ Deman, p. 488.
‘La donnée naturelle ne suffit pas à tout. Et l’éducation concernera les connaissances dont la conscience doit être l’application pratique ainsi que les dispositions affectives inevitable engagees dans l’action.’ Deman, p. 489.
Deman, 495.
Aquinas’ biblical commentaries are available at (accessed on 30 July 2022).
‘… chacune des deux notions garde son entire raison d’être’. Deman, La Prudentia, p. 497.
‘Nous avons signalé dans saint Paul la première origine certaine de cette function de la conscience.’ Deman, p. 497.
Haec omnia consequuntur applicationem alicuius nostrae cognitionis vel scientiae ad ea quae agimus.
Habitus autem ex quibus conscientia informatur, etsi multi sint, omnes tamen efficaciam habent ab uno primo, scilicet ab habitu primorum principiorum, qui dicitur synderesis.
Deman, La Prudentia, 498.
Jerome’s use of synderesis is said to have resulted from the scribal confusion of syneidesis with synderesis. Over the centuries, the distinctive meaning of these two terms, synderesis and syneidesis, has attracted attention, and potential confusion. Aquinas is free of this confusion since he simply uses synderesis. See (Hogan 2006).
Bourke, “The Synderesis Rule and Right Reason” p. 71.
Bourke, “The Synderesis Rule and Right Reason”, p. 75.
‘L’homme, peut-on dire, naît à la vie morale dans l’instant où il forme ce jugement dont le bien est l’objet.’ Deman, La Prudentia, p. 436.
Deman, La Prudentia, p. 499.
Commenting on the attempts of other theologians of the time who tried to introduce distinctions to ameliorate this teaching of the binding character of a false conscience, Deman judges their ingenuity to be futile (‘Leur ingéniosité est vaine’). Deman, 499.
Quia obiectum voluntatis est id quod proponitur a ratione.
‘L’example est hardi.’ Deman, La Prudentia, 500.
‘En théologie chrétienne, où la règle raisonnable n’est qu’une dérivation de la loi divine, la force obligatoire de la conscience n’est aussi au’une expression de la volonté de Dieu.’ Deman, 500. Also see De Veritate q. 17 a.5.
Thomas Deman, “The School of Conscience”, p. 132.
Deman, La Prudentia, 501.
Deman, 503.
Deman, “The School of Conscience”, 134.
‘… à l’intérieur de la vertu de prudence’, Deman, La Prudentia, 504.
‘N’en viendra-t-on pas à deplorer qu’ils aient trop de conscience?’ Deman, 506.
‘D’une certaine manière, il apparaîtrait moins consciencieux s’il était plus profondément vertueux.’ Deman, 506.
‘un empressement et, pour dire le mot, avec une élégance qui dénonee dans l’âme une moralité consomée.’ Deman, 506.
Deman, 506.


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