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Praying With Non-Catholics — Is it Possible?

By Fr. Thomas Crean O.P.

This article seeks to offer a theological reflection on a not unknown feature of the contemporary Christian world, namely public divine worship performed jointly by Catholics and non-Catholics. I shall consider first, by way of historical background, the traditional teaching of theologians on communicatio in sacris; secondly, the references to communicatio in sacris and to common prayer in Vatican II’s ‘Decree on Ecumenism’ and in some subsequent documents; and finally, whether certain current practices of common prayer are theologically defensible. I shall not consider the reception by Catholics of sacraments from non-Catholic ministers, nor the converse, as such practices do not of themselves imply a common, public worship.

Communicatio in sacris

The traditional teaching of Catholic theology on whether Catholics may participate in non-Catholic religious services is summed up by St Alphonsus Liguori in his Theologia Moralis. This doctor of the church writes, It is not permitted to be present at the sacred rites of infidels and heretics in such a way that you would be judged to be in communion with them’.1 The reason for this teaching is clear: religious commitments are naturally manifested by outward acts; and to perform an outward act expressive of a false religious commitment is a sin against the true faith. This is true even if the man in question retains the true faith in his heart. So to take the classic example, Christians in the Roman Empire realised that they must not throw incense before a statue of the Emperor, even if they had no belief at all in his divinity – for the act was of itself, in their context, expressive of such a belief, and hence sinful.

This teaching does not imply that the simple presence of a Catholic at a non-Catholic religious service is a sin. Thus moral theologians prior to Vatican II, following the lead of St Alphonsus, acknowledge that there may be a good reason for a Catholic to attend such a service, as when friendship leads one to attend a non-Catholic wedding. This is called by some theologians ‘passive communicatio in sacris’. It is active participation in a non-Catholic religious service which is forbidden by the traditional teaching on communicatio in sacris, for example joining in with psalms and hymns in the course of a Lutheran Eucharist. The following examples may serve to show the unanimity of pre-conciliar theologians on this point.

Fr. D. Prummer OP, writing in 1910, affirms in his Manuale Theologiæ Moralis that it is never licit for a Catholic to take part in a non-Catholic cult with the intention of worshipping God in the manner of non-Catholics, more acatholicorum. Such an act, he declares, is nothing other than a denial of the Catholic faith.2 In the same year, writing an article on ‘Heresy’ for the Catholic Encyclopœdia, Fr. J. Wilhelm SJ affirms that a Catholic may attend non-Catholic services, but only provided no active part be taken in them’. In an article on the same subject, the Dictionnaire de théologie catholique reiterates, in 1920, that active participation in non-Catholic rites is toujours interdite – the reason being that it is equivalent to a denial of the Catholic faith. In 1930, Fr. B. Merkelbach OP in his Summa Theologiæ Moralis writes that active participation in the sacred things of a [non-Catholic] public cult is illicit, since it implies approval of the worship and a recognition of the sect.3 Using a slightly different terminology but teaching the same doctrine, Fr. L. Fanfani OP writes, in 1950, material communicatio in sacris [‘material’ in the sense that the person in question does not mean to renounce his Catholic faith], if it is active and immediate, is never permissible for Catholics.4 The reason for this, he explains, is that such behaviour necessarily manifests a commitment to a heretical or at least an illegitimate cultus.

It is important to notice that this prohibition is not presented by these theologians as an ecclesiastical ban. It is not the law of the Church which is traditionally understood to exclude Catholics from taking part in non-Catholic services; it is the divine law, which requires that outward acts of worship be expressive of inward faith. Nor is common worship only forbidden when the prayers or scriptural translations used by the non-Catholic group have an heretical sense: the mere act of sharing the worship of a non-Catholic group, according to the teaching of the theologians cited above, implies a community of religion with that group, and hence constitutes a sin against the faith. This explains why, as Pius XI recalled in the 1928 encyclical Mortalium Animos, [the] Apostolic See has never allowed its subjects to take part in the assemblies of non-Catholics.

There are two more features of this traditional teaching which are relevant to the subject of this article. Whilst active communicatio in sacris is always judged impossible for a Catholic, the same is not true for a non-Catholic. It is not only not forbidden, it is in itself good that a non-Catholic should enter a Catholic Church to assist at the Mass or the divine office. Secondly, it is not considered impossible that a Catholic and a non-Catholic should pray together outside the context of public divine worship. Thus Fanfini remarks that for a Catholic and a non-Catholic to say the ‘Our Father’ together in private is permissible in certain circumstances, and is not in fact a sacrum, a sacred rite, at all.5

Unitatis Redintegratio and beyond

The Second Vatican Council gave its endorsement to work for the unity of Christians in the Decree Unitatis Redintegratio. After laying down in its first part some Catholic principles on ecumenism, the document goes on to speak of ecumenism in practice. In speaking of the necessary rôle played in the search for unity by conversion of heart and by prayer, it affirms:

In certain circumstances, such as prayers ‘for unity’ and during ecumenical gatherings, it is allowable, indeed desirable that Catholics should join in prayer with their separated brethren.6

Does this statement contradict the traditional teaching on communicaio in sacris which has just been outlined? No, for it is not stated that this common prayer must involve Catholics taking part in any prayers others than ones authorised by the Catholic Church and led by her sacred ministers. The Council Fathers however do not directly seek to relate their remarks about common prayer to what I have called the traditional teaching on communicatio in sacris; instead they go on to state that two principles must be borne in mind to establish a sound doctrine on such communicatio, namely the need for the unity of the Church to be visibly manifested and the grace that may be obtained thereby’. They further remark :

The expression of unity very generally [plerumque] forbids common worship [communicationem]. Grace to be obtained sometimes commends it.7

The Council Fathers say no more in this place about the practical implications of all this, save that it is best left to the prudence of the local bishop. Nor do they state whether the communicatio in sacris which is sometimes to be welcomed as a means of grace is an  active or passive communicatio, nor in what ‘direction’ the communicatio should go: thus they do not state whether what is to be sometimes welcomed is the active participation by Catholics in non-Catholic services, or the active participation by non-Catholics in Catholic services, or the simple presence of a Catholic at non-Catholic services, or the simple presence of a non-Catholic at Catholic services, or the active presence by both Catholics and non-Catholics at specially designed ‘ecumenical services’. It may be that all five of these forms of communicatio in sacris would, in fact, have been accepted or welcomed by the Fathers of the Council: but the text itself does not tell us.

Towards the end of the document, in section 15, the Fathers re-affirm that some forms of communicatio in sacris with the separated Eastern Churches are to be encouraged, given the valid sacraments enjoyed by these communities; again, however, they do not say whether it is Catholics who are to be encouraged to communicate in the sacra of the Eastern brethren, or they who are to be encouraged to communicate in ours. Nor is it specified whether such communication is to be active or passive; thus a Catholic who attended a liturgy in a separated Eastern community to ‘savour the atmosphere’ and to pray privately would be engaging in a form of passive communicatio – and the Council Fathers do not expressly say that it is anything more than this which is to be ‘encouraged’.

These considerations seem to show that the text of Unitatis Redintegratio contains nothing which contradicts the traditional teaching of theologians on communicatio in sacris. Whenever this practice is commended by the conciliar document, it is never explicitly said that it is active participation by a Catholic in non-Catholic services which is in question. Such may have been the ‘mood’ of the Council – but it is not the letter of the text.8

On 14th May 1967, the Secretariat for the Promotion of the Unity of Christians – a body set up in 1960 for a practical rather than a strictly doctrinal purpose - issued a document called Ad Totam Ecclesiam, being the first part of an ‘ecumenical directory’. In two key respects Ad Totam Ecclesiam goes beyond the letter of Unitatis Redintegratio. First of all, it expands the Council’s remark about the desirability of common prayer at prayer services for unity and during ecumenical gatherings. As it describes this common prayer, it is to be a matter not of non-Catholics joining in with Catholic services, nor of Catholics and non-Catholics praying together silently (both alternatives which were left open by the text of Unitatis Redintegratio), but rather of the participation of Catholics and non-Catholics in forms of public worship specially designed by representatives of their various communities. These representatives should agree and co-operate…in deciding who should take part, what themes, hymns, scripture readings and the like should be used. Such services, the document further states, should be modelled on the forms of community prayer recommended by the liturgical revival’.9

Does this contradict the traditional teaching of theologians on communicatio in sacris ? At first sight, it seems to offer a new case, one not considered by the pre-conciliar theologians: for it is not a question of Catholics joining in with Protestant (or Orthodox or non-Christian) services, but of their joining in with other Christians in services designed to be simply Christian services, and as such acceptable to all concerned. This question will be looked at in the last section of this article.

The second innovation of Ad Totam Ecclesiam, however, does contradict the traditional teaching of theologians on communicatio in sacris. The authors affirm that not only may a Catholic attend the services of an Orthodox community or of a Protestant one, he may also take part in the common responses, hymns and actions of the community in question, so long as they are not at variance with Catholic faith’.10 Pre-conciliar authors, as we have seen, would have considered this a manifestation of allegiance to a cultus which was heretical or at least objectively illegitimate, and as such a fault against the virtue of faith.

The Catechism of the Catholic Church, in its section on the unity of the Church, does not use the term communicatio in sacris. It does however refer very briefly to the question of prayer in common with non-Catholics. The Catechism states that prayer in common is a necessary part of the ecumenical movement, and it then quotes the following sentence from Unitatis Redintegratio:

Change of heart and holiness of life, along with private and public prayer for the unity of Christians, should be regarded as the soul of the whole ecumenical movement.11

Does this statement imply the adoption by the Catechism of Ad Totam Ecclesiam’s first innovation, that of specially prepared ecumenical services ? Not necessarily, for as we have seen in the case of Unitatis Redintegratio, this recommendation of shared public prayer for the unity of Christians could be fulfilled by the participation of non-Catholics in Catholic services; all the more so, as this sentence from Unitatis Redintegratio immediately precedes one where the Council Fathers descibe the long-established custom of Catholics as such praying publicly for the fulfilment of Christ’s prayer, ut unum sint.

Finally, Pope John Paul II, in the encyclical letter Ut Unum Sint, similarly commends the practice of common prayer between Catholics and others, but does not stipulate in what such prayer should consist. He thus lays down as binding upon Catholics no more than was laid down some thirty years earlier by the Second Vatican Council.

What sort of common prayer is possible ?

Thus far we have argued that Unitatis Redintegratio and subsequent magisterial documents contain nothing which formally contradicts the traditional teaching of theologians on communicatio in sacris. However, as we have also seen, another document, produced by a body whose function was apparently practical rather than doctrinal, does both formally contradict this teaching, and also introduce an apparently new question, that of the ‘ecumenical prayer service’. In this last section we shall offer some remarks on these two innovations made by the Secretariat for the Promotion of the Unity of Christians.

First of all, how might a proponent of the participation by Catholics in Orthodox or Protestant worship answer traditional theology’s condemnation of this? Quite commonly it is said that to-day, ‘we are in a new context’. Thus while in the past such participation might have been seen as a rejection of one’s own Church, or at least as culpable indifference towards it, to-day Christians are increasingly under siege from secular society, and so may rightly make common cause against it.

Yet to this one may reply that whilst our circumstances to-day are no doubt very different from those of the 16th Century, or of the 11th, circumstances alone may never justify an act which is intrinsically unlawful. Classical theology is unanimous in maintaining that the active participation by Catholics in, for example, a Protestant service, is unlawful of itself and not simply if it may give scandal by virtue of the circumstances, or if the ultimate intention of the Catholic is to belittle his own church. The reason for this, as we have seen, is that such worship of itself expresses unity of religion; the good faith of the worshippers is, in this sense, irrelevant.

A defender of such worship might object: still, the history of salvation gives us examples of actions which at one epoch are rightly regarded as intrinsically unlawful, and yet which are permitted, and even rewarded, by God at another – for example, polygamy. Could not participation in non-Catholic services be an example of such an action?

To this one may reply that the history of salvation shows us how man has been gradually enlightened concerning the demands of natural law, and has thus been gradually led to a stricter and more perfect morality. There are however no examples of man being gradually led by divine inspiration to practice a less strict adherence to the moral law. In the specific case of polygamy, St Thomas teaches that a dispensation was possible for the patriarchs insofar as the practice would leave intact the primary purpose of matrimony, the begetting of children, and impair only the second, the companionship of husband and wife. Polyandry, he further notes, could never be permitted, as this would harm the primary purpose of marriage. In the case of public divine worship the primary purpose is that God should be duly honoured, and the building up of fraternal ties between the worshippers is only the secondary purpose. Thus even supposing, per impossibile, that humanity was being divinely inspired to fulfil the demands of natural law less perfectly than before in regard to divine worship, it could not be in the way suggested by the objection, as this would involve sacrificing the primary purpose of divine worship to the secondary purpose.

We thus conclude that the traditional strictures against active participation by Catholics in non-Catholic services retain their compelling force.

Secondly, what of ‘ecumenical services’? (By this term I understand services where Catholics and non-Catholics come together to offer divine worship according to a text and ritual designed to be thus used in common.) As we have seen, the schola of pre-conciliar theologians states that Catholics should never participate actively in non-Catholic worship as this would manifest adherence to a non-Catholic religion. How might a defender of ecumenical worship as it is commonly found to-day respond to this stern injunction? He could either deny that ecumenical worship is rightly described as ‘non-Catholic’ worship, or else deny that it manifests adherence to a non-Catholic religion.

To begin with the first option. The adage lex orandi, lex credendi shows that the religious character of a given form of worship is determined by the beliefs which it incorporates: Catholic worship is Catholic because it incorporates Catholic beliefs and Protestant worship is Protestant because it incorporates Protestant beliefs. What are the beliefs which ecumenical worship, as such, incorporates ? Clearly, the beliefs deemed to be common to all the great historic forms of Christianity. Thus many doctrines of the Catholic faith may be expressed in such worship: yet they will not be present because they are Catholic, but for another reason, namely that they are accepted by certain non-Catholics. Ecumenical worship, formally speaking, is thus not Catholic, because it is not designed to express Catholicism as such; it is therefore a non-Catholic worship.

Someone might object: it is true that ecumenical worship, for a non-Catholic, is not an expression of Catholic faith, for he does not have this faith to express; yet on the part of the Catholic, this worship does express the true faith, for all the doctrines expressed by the worship are held by the Catholic precisely in virtue of his Catholic faith. Thus the service is, from his point of view, a Catholic religious service, and thus legitimate.

Yet this seems insufficient. For a religious service to be genuinely Catholic, the beliefs which it conveys must be present because they are taught by the Catholic Church to be revealed by God. Otherwise it will be, at best, materially Catholic, but formally not. And the criterion which the organisers of an ecumenical service use in deciding which doctrines may be expressed in their service is not the teaching of the Catholic Church, but a de facto agreement between Catholics and others as to the truth of these doctrines. The fact that a Catholic participant believes in all these doctrines because they have been proposed to him by the Church does not change the fact that he is participating in a worship which is formally non-Catholic, just as much as he would be if he were, say, singing psalms at a Lutheran Eucharist – and this, if we accept the traditional teaching of theologians, is not possible.

The only way of denying that ecumenical services were forms of non-Catholic worship would be to deny that they had any true unity. Thus it might be said that although the various participants were, materially, performing the same actions, yet because of their different religious view-points, they were not participants in one and the same service; by singing hymns and psalms together, and offering the same prayers with one voice, Catholics and Protestants, say, were in fact offering two different services, one Catholic, one Protestant. And perhaps this is the best description of what is really happening at an ecumenical service, when all the parties act in good faith. Yet if this is what is happening, is it defensible? It would seem not, and for two reasons. First of all, it would mean worshipping God with a worship which is not what it seems – appearing to be offering a worship in union with all present, but in reality not doing so. And that is surely not tolerable – non enim est dissensionis Deus sed pacis (1 Cor. 14 :33). Secondly it would imply, at least on the part of the organisers of the service, an invitation to non-Catholics to do something objectively illegitimate, namely, to offer non-Catholic public worship.

Now to consider the second alternative : a proponent of ecumenical worship might well accept that such worship was not formally Catholic, yet go on to argue that it remains nevertheless untouched by pre-conciliar strictures against forbidden communicatio in sacris. Such strictures, he might say, apply only to those forms of non-Catholic worship which manifest adherence to a non-Catholic religion. Ecumenical worship, he might add, may indeed not express adherence to the Catholic religion; yet nor does it express adherence to a non-Catholic religion – for it does not express adherence to any religion. It is precisely designed to allow different Christians to worship God together without expressing adherence to a common understanding of Christianity. It is therefore legitimate.

Such a view is plausible; but is it tenable ? Can there really be a public, divine worship which manifests adherence to no definite religion ?

Let us consider what a human being, whatever his religion, seeks by engaging in a religious act. He is seeking to put himself or to maintain himself in a right relation with the Deity: that is what makes his act religious. He is not seeking merely to express certain convictions about God, as someone might do by filling in a questionnaire – he is seeking to come into the presence of God, and to be ‘ordered’ to God as God Himself wills. So by engaging in a given religious act, a person expresses his desire to be in a right relationship with God by means of it. But now let us assume that the religious act in question is a public act, i.e. the act of a community. By engaging in this essentially public act, the person would now be expressing his desire to be in a right relationship with God in or by means of this community. For since it is the community which is the subject of the religious act in question, by becoming a part of the acting community, he signifies that it has, for him, the power to perform a properly religious act, that is, to put him in a due relation to God. He may not in fact believe this – but it is what his act, as such, signifies.

Common worship need not imply a complete agreement on all matters concerning God and man. Thus within the Catholic Church, a Scotist and a Thomist may happily worship together. But if the foregoing reasoning is correct, common worship does imply an agreement that the community which thus worships together is a community in which God wills to be worshipped, and which is able to put one in a due relation with Him. In this sense, common worship does imply a common religion.

The Catholic, however, believes that it is in the visible Catholic Church, and only there, that God wills to be worshipped and that he can save his soul. He does not believe that any other community can bring him into a right relationship with God or maintain him in such a relation, except the Church. By engaging in ecumenical worship, therefore, he would seem to be in a contradictory position; he would be manifesting a religious commitment to a community which he believes has for him no salvific power, no power to put him in a due relationship with God. His act, as a public religious act, implies that he attributes such a religious power to the community; his faith forbids him to believe this. For he believes that if he left the Catholic Church, even to engage in exclusively ecumenical worship, he would lose his soul.

One may note that the same contradiction need not apply to Protestants from various denominations engaging in public prayer together. Though they may have serious disagreements, even on the very content of divine revelation – eg on whether it is God’s will that babies should be baptised -, they would typically believe that it is possible to save one’s soul in a community where prayer is offered in Christ’s name and ‘the word of God is preached’. Such a community could be composed of members of various denominations gathered together. The Catholic, however, believes that it is in one particular, historical body, the Catholic Church, that God wills to be worshipped. In this respect, the disagreements of the various Protestant denominations are more akin to those which may exist between Catholic theologians of disparate ‘schools’.

One may further note that if, as we have argued, ecumenical worship places the Catholic in an anomalous position, he may not escape the anomaly by deciding or even expressly stating that in his case, such worship will not express a community of religion with those with whom he publicly worships but will simply be a gesture of good will towards them. For the expression of community of religion is intrinsic to the act of common worship, and not dependent upon the worshipper’s intention: it is a finis operis and not a finis operantis. In the same way, if someone told a lie to give pleasure to another, though his good intention would mitigate his act, he could not defend himself on the grounds that ‘he had decided’ that his words would, in this case, be an expression not of his thought but simply of his good will towards his interlocutor. For it is an intrinsic property of speech that it should express a thought.

To pursue the analogy: one could of course say words which were materially false to a group where everyone knew perfectly well that one did not mean them. This would then be not lying, but joking or play-acting. But such an exception evidently can give the Catholic no charter for ecumenical worship. Even supposing that the non-Catholics present knew perfectly well that he believed that God willed to be worshipped only in the Catholic Church, would they be happy, would it be consonant with reverence, that he should actively participate in an ecumenical service only on the clear understanding that this was for him but a pretence or a game?

Finally, what of the common affirmation that whilst it is impossible for Catholics to celebrate the Holy Eucharist with those who are not in full communion with us, ecumenical worship is the just expression of the real, but partial communion which we have with our separated brethren? It is of course right that this ‘imperfect communion’ should be recognised, and that our common allegiance to Christ manifested as far as possible. This could be done, for example, by Catholics and other Christians coming together to pray in silence before a crucifix or an icon of the Saviour. But as soon as the worship becomes genuinely public worship, following a text and ritual agreed with non-Catholics and perhaps even led by someone who is not a Catholic minister – and that perhaps even in the presence of Catholic clergy – then the act becomes the act of a non-Catholic community, and by participating in it, a Catholic is attributing a religious, salvific power to a community which he knows cannot save him.


In this article I have argued that the teaching of pre-conciliar theologians on communicatio in sacris is formally compatible with the teaching of the Second Vatican Council (though not with a later document published by the Secretariat for the Promotion of Christian Unity, a body whose function was practical rather than doctrinal.) I have also argued in defence of the traditional teaching that public worship in common with non-Catholics, except within explicitly Catholic services, implies a religious commitment which is logically incompatible with commitment to the visible Catholic Church as the One Ark of salvation. I have argued this last point especially with regard to that sort of worship which might seem most plausibly to demand a development of the traditional teaching, namely ecumenical worship; if my reasoning is correct, then it must apply a fortiori to active participation in the services of another Church or ecclesial community.


1. ‘
Infidelium et haereticorum sacris non licet ita interesse, ut eis communicare censearis’, Theologia Moralis, Lib.5, Tract. 1, Cap. 3.

2. Manuale Theologiæ Moralis, Tomus I, Tract. VII, art. III.

3. ‘Communicatio activa seu participatio in ipsis sacris, scil. cultus publici'.  Summa Theologiæ Moralis, I, 754.

4.‘Etiam communicatio materialis in sacris, si est activa et immediata, nunquam catholicis licet…Re quidem vera, talis communicatio importat exercere actionem, etsi materialiter tantum, quae ex se vel ex circumstantiis necessario sese refert ad cultum falsum vel saltem illegitimum..Nunquam autem licet, neque externe tantum, adhaerere falsae religioni vel negare veram.Manuale Theorico-Practicum Theologiæ Moralis, Tomus II, Tract. II, Cap. IV, 38.

5. Ibid.

6. U.R. 8

7. Ibid.

8. The ‘History of the Decree’ written by W.Becker (in the Commentary on the Documents of Vatican II, ed. H. Vorgrimler, Vol. II p.36) suggests that some of the Fathers would have favoured active participatio by eastern Catholics in Orthodox worship. However, even in the provisions for communicatio in sacris laid down by the Decree on Eastern Catholic Churches, 26 & 29, this is not explicitly commended; though these paragraphs seem in any case disciplinary, rather than doctrinal in character.

9. Ad Totam Ecclesiam, 35.

10. A. T. E. 50 & 59.

11. Catechism of the Catholic Church, 821.

This article first appeared in Apropos and is reproduced with permission.

Version: 8th February 2009

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